diff --git a/apps/macos/Sources/Clawdbot/ChannelsSettings+ChannelState.swift b/apps/macos/Sources/Clawdbot/ChannelsSettings+ChannelState.swift
index 79dd97cf9..a43e7d56b 100644
--- a/apps/macos/Sources/Clawdbot/ChannelsSettings+ChannelState.swift
+++ b/apps/macos/Sources/Clawdbot/ChannelsSettings+ChannelState.swift
@@ -40,6 +40,17 @@ extension ChannelsSettings {
         return .orange
     }
 
+    var mattermostTint: Color {
+        guard let status = self.channelStatus("mattermost", as: ChannelsStatusSnapshot.MattermostStatus.self)
+        else { return .secondary }
+        if !status.configured { return .secondary }
+        if status.lastError != nil { return .orange }
+        if status.probe?.ok == false { return .orange }
+        if status.connected == true { return .green }
+        if status.running { return .orange }
+        return .orange
+    }
+
     var signalTint: Color {
         guard let status = self.channelStatus("signal", as: ChannelsStatusSnapshot.SignalStatus.self)
         else { return .secondary }
@@ -85,6 +96,15 @@ extension ChannelsSettings {
         return "Configured"
     }
 
+    var mattermostSummary: String {
+        guard let status = self.channelStatus("mattermost", as: ChannelsStatusSnapshot.MattermostStatus.self)
+        else { return "Checking…" }
+        if !status.configured { return "Not configured" }
+        if status.connected == true { return "Connected" }
+        if status.running { return "Running" }
+        return "Configured"
+    }
+
     var signalSummary: String {
         guard let status = self.channelStatus("signal", as: ChannelsStatusSnapshot.SignalStatus.self)
         else { return "Checking…" }
@@ -193,6 +213,38 @@ extension ChannelsSettings {
         return lines.isEmpty ? nil : lines.joined(separator: " · ")
     }
 
+    var mattermostDetails: String? {
+        guard let status = self.channelStatus("mattermost", as: ChannelsStatusSnapshot.MattermostStatus.self)
+        else { return nil }
+        var lines: [String] = []
+        if let source = status.botTokenSource {
+            lines.append("Token source: \(source)")
+        }
+        if let baseUrl = status.baseUrl, !baseUrl.isEmpty {
+            lines.append("Base URL: \(baseUrl)")
+        }
+        if let probe = status.probe {
+            if probe.ok {
+                if let name = probe.bot?.username {
+                    lines.append("Bot: @\(name)")
+                }
+                if let elapsed = probe.elapsedMs {
+                    lines.append("Probe \(Int(elapsed))ms")
+                }
+            } else {
+                let code = probe.status.map { String($0) } ?? "unknown"
+                lines.append("Probe failed (\(code))")
+            }
+        }
+        if let last = self.date(fromMs: status.lastProbeAt ?? status.lastConnectedAt) {
+            lines.append("Last probe \(relativeAge(from: last))")
+        }
+        if let err = status.lastError, !err.isEmpty {
+            lines.append("Error: \(err)")
+        }
+        return lines.isEmpty ? nil : lines.joined(separator: " · ")
+    }
+
     var signalDetails: String? {
         guard let status = self.channelStatus("signal", as: ChannelsStatusSnapshot.SignalStatus.self)
         else { return nil }
@@ -244,7 +296,7 @@ extension ChannelsSettings {
     }
 
     var orderedChannels: [ChannelItem] {
-        let fallback = ["whatsapp", "telegram", "discord", "slack", "signal", "imessage"]
+        let fallback = ["whatsapp", "telegram", "discord", "slack", "mattermost", "signal", "imessage"]
         let order = self.store.snapshot?.channelOrder ?? fallback
         let channels = order.enumerated().map { index, id in
             ChannelItem(
@@ -307,6 +359,8 @@ extension ChannelsSettings {
             return self.telegramTint
         case "discord":
             return self.discordTint
+        case "mattermost":
+            return self.mattermostTint
         case "signal":
             return self.signalTint
         case "imessage":
@@ -326,6 +380,8 @@ extension ChannelsSettings {
             return self.telegramSummary
         case "discord":
             return self.discordSummary
+        case "mattermost":
+            return self.mattermostSummary
         case "signal":
             return self.signalSummary
         case "imessage":
@@ -345,6 +401,8 @@ extension ChannelsSettings {
             return self.telegramDetails
         case "discord":
             return self.discordDetails
+        case "mattermost":
+            return self.mattermostDetails
         case "signal":
             return self.signalDetails
         case "imessage":
@@ -377,6 +435,10 @@ extension ChannelsSettings {
             return self
                 .date(fromMs: self.channelStatus("discord", as: ChannelsStatusSnapshot.DiscordStatus.self)?
                     .lastProbeAt)
+        case "mattermost":
+            guard let status = self.channelStatus("mattermost", as: ChannelsStatusSnapshot.MattermostStatus.self)
+            else { return nil }
+            return self.date(fromMs: status.lastProbeAt ?? status.lastConnectedAt)
         case "signal":
             return self
                 .date(fromMs: self.channelStatus("signal", as: ChannelsStatusSnapshot.SignalStatus.self)?.lastProbeAt)
@@ -411,6 +473,10 @@ extension ChannelsSettings {
             guard let status = self.channelStatus("discord", as: ChannelsStatusSnapshot.DiscordStatus.self)
             else { return false }
             return status.lastError?.isEmpty == false || status.probe?.ok == false
+        case "mattermost":
+            guard let status = self.channelStatus("mattermost", as: ChannelsStatusSnapshot.MattermostStatus.self)
+            else { return false }
+            return status.lastError?.isEmpty == false || status.probe?.ok == false
         case "signal":
             guard let status = self.channelStatus("signal", as: ChannelsStatusSnapshot.SignalStatus.self)
             else { return false }
diff --git a/apps/macos/Sources/Clawdbot/ChannelsStore.swift b/apps/macos/Sources/Clawdbot/ChannelsStore.swift
index e62e737a4..810261b9e 100644
--- a/apps/macos/Sources/Clawdbot/ChannelsStore.swift
+++ b/apps/macos/Sources/Clawdbot/ChannelsStore.swift
@@ -85,6 +85,40 @@ struct ChannelsStatusSnapshot: Codable {
         let lastProbeAt: Double?
     }
 
+    struct MattermostBot: Codable {
+        let id: String?
+        let username: String?
+    }
+
+    struct MattermostProbe: Codable {
+        let ok: Bool
+        let status: Int?
+        let error: String?
+        let elapsedMs: Double?
+        let bot: MattermostBot?
+    }
+
+    struct MattermostDisconnect: Codable {
+        let at: Double
+        let status: Int?
+        let error: String?
+    }
+
+    struct MattermostStatus: Codable {
+        let configured: Bool
+        let botTokenSource: String?
+        let running: Bool
+        let connected: Bool?
+        let lastConnectedAt: Double?
+        let lastDisconnect: MattermostDisconnect?
+        let lastStartAt: Double?
+        let lastStopAt: Double?
+        let lastError: String?
+        let baseUrl: String?
+        let probe: MattermostProbe?
+        let lastProbeAt: Double?
+    }
+
     struct SignalProbe: Codable {
         let ok: Bool
         let status: Int?
diff --git a/apps/macos/Sources/Clawdbot/GatewayConnection.swift b/apps/macos/Sources/Clawdbot/GatewayConnection.swift
index 36e8fc62b..6a69d7860 100644
--- a/apps/macos/Sources/Clawdbot/GatewayConnection.swift
+++ b/apps/macos/Sources/Clawdbot/GatewayConnection.swift
@@ -12,6 +12,7 @@ enum GatewayAgentChannel: String, Codable, CaseIterable, Sendable {
     case telegram
     case discord
     case slack
+    case mattermost
     case signal
     case imessage
     case msteams
diff --git a/apps/macos/Tests/ClawdbotIPCTests/ChannelsSettingsSmokeTests.swift b/apps/macos/Tests/ClawdbotIPCTests/ChannelsSettingsSmokeTests.swift
index 2b1eced84..08c05a77c 100644
--- a/apps/macos/Tests/ClawdbotIPCTests/ChannelsSettingsSmokeTests.swift
+++ b/apps/macos/Tests/ClawdbotIPCTests/ChannelsSettingsSmokeTests.swift
@@ -12,10 +12,11 @@ struct ChannelsSettingsSmokeTests {
         let store = ChannelsStore(isPreview: true)
         store.snapshot = ChannelsStatusSnapshot(
             ts: 1_700_000_000_000,
-            channelOrder: ["whatsapp", "telegram", "signal", "imessage"],
+            channelOrder: ["whatsapp", "telegram", "mattermost", "signal", "imessage"],
             channelLabels: [
                 "whatsapp": "WhatsApp",
                 "telegram": "Telegram",
+                "mattermost": "Mattermost",
                 "signal": "Signal",
                 "imessage": "iMessage",
             ],
@@ -57,6 +58,21 @@ struct ChannelsSettingsSmokeTests {
                     ],
                     "lastProbeAt": 1_700_000_050_000,
                 ]),
+                "mattermost": SnapshotAnyCodable([
+                    "configured": true,
+                    "botTokenSource": "env",
+                    "running": true,
+                    "connected": true,
+                    "baseUrl": "https://chat.example.com",
+                    "lastStartAt": 1_700_000_000_000,
+                    "probe": [
+                        "ok": true,
+                        "status": 200,
+                        "elapsedMs": 95,
+                        "bot": ["id": "bot-123", "username": "clawdbot"],
+                    ],
+                    "lastProbeAt": 1_700_000_050_000,
+                ]),
                 "signal": SnapshotAnyCodable([
                     "configured": true,
                     "baseUrl": "http://127.0.0.1:8080",
@@ -82,6 +98,7 @@ struct ChannelsSettingsSmokeTests {
             channelDefaultAccountId: [
                 "whatsapp": "default",
                 "telegram": "default",
+                "mattermost": "default",
                 "signal": "default",
                 "imessage": "default",
             ])
@@ -98,10 +115,11 @@ struct ChannelsSettingsSmokeTests {
         let store = ChannelsStore(isPreview: true)
         store.snapshot = ChannelsStatusSnapshot(
             ts: 1_700_000_000_000,
-            channelOrder: ["whatsapp", "telegram", "signal", "imessage"],
+            channelOrder: ["whatsapp", "telegram", "mattermost", "signal", "imessage"],
             channelLabels: [
                 "whatsapp": "WhatsApp",
                 "telegram": "Telegram",
+                "mattermost": "Mattermost",
                 "signal": "Signal",
                 "imessage": "iMessage",
             ],
@@ -128,6 +146,19 @@ struct ChannelsSettingsSmokeTests {
                     ],
                     "lastProbeAt": 1_700_000_100_000,
                 ]),
+                "mattermost": SnapshotAnyCodable([
+                    "configured": false,
+                    "running": false,
+                    "lastError": "bot token missing",
+                    "baseUrl": "https://chat.example.com",
+                    "probe": [
+                        "ok": false,
+                        "status": 401,
+                        "error": "unauthorized",
+                        "elapsedMs": 110,
+                    ],
+                    "lastProbeAt": 1_700_000_150_000,
+                ]),
                 "signal": SnapshotAnyCodable([
                     "configured": false,
                     "baseUrl": "http://127.0.0.1:8080",
@@ -154,6 +185,7 @@ struct ChannelsSettingsSmokeTests {
             channelDefaultAccountId: [
                 "whatsapp": "default",
                 "telegram": "default",
+                "mattermost": "default",
                 "signal": "default",
                 "imessage": "default",
             ])
diff --git a/apps/macos/Tests/ClawdbotIPCTests/GatewayAgentChannelTests.swift b/apps/macos/Tests/ClawdbotIPCTests/GatewayAgentChannelTests.swift
index bf72af7e5..a19c49bfc 100644
--- a/apps/macos/Tests/ClawdbotIPCTests/GatewayAgentChannelTests.swift
+++ b/apps/macos/Tests/ClawdbotIPCTests/GatewayAgentChannelTests.swift
@@ -11,6 +11,7 @@ import Testing
         #expect(GatewayAgentChannel.last.shouldDeliver(true) == true)
         #expect(GatewayAgentChannel.whatsapp.shouldDeliver(true) == true)
         #expect(GatewayAgentChannel.telegram.shouldDeliver(true) == true)
+        #expect(GatewayAgentChannel.mattermost.shouldDeliver(true) == true)
         #expect(GatewayAgentChannel.bluebubbles.shouldDeliver(true) == true)
         #expect(GatewayAgentChannel.last.shouldDeliver(false) == false)
     }
diff --git a/docs/automation/cron-jobs.md b/docs/automation/cron-jobs.md
index 882cf816a..a5c24abd8 100644
--- a/docs/automation/cron-jobs.md
+++ b/docs/automation/cron-jobs.md
@@ -121,7 +121,7 @@ Resolution priority:
 
 ### Delivery (channel + target)
 Isolated jobs can deliver output to a channel. The job payload can specify:
-- `channel`: `whatsapp` / `telegram` / `discord` / `slack` / `signal` / `imessage` / `last`
+- `channel`: `whatsapp` / `telegram` / `discord` / `slack` / `mattermost` / `signal` / `imessage` / `last`
 - `to`: channel-specific recipient target
 
 If `channel` or `to` is omitted, cron can fall back to the main session’s “last route”
@@ -133,7 +133,7 @@ Delivery notes:
 - Use `deliver: false` to keep output internal even if a `to` is present.
 
 Target format reminders:
-- Slack/Discord targets should use explicit prefixes (e.g. `channel:<id>`, `user:<id>`) to avoid ambiguity.
+- Slack/Discord/Mattermost targets should use explicit prefixes (e.g. `channel:<id>`, `user:<id>`) to avoid ambiguity.
 - Telegram topics should use the `:topic:` form (see below).
 
 #### Telegram delivery targets (topics / forum threads)
diff --git a/docs/automation/webhook.md b/docs/automation/webhook.md
index f2a62b4e3..4556b4111 100644
--- a/docs/automation/webhook.md
+++ b/docs/automation/webhook.md
@@ -71,8 +71,8 @@ Payload:
 - `sessionKey` optional (string): The key used to identify the agent's session. Defaults to a random `hook:<uuid>`. Using a consistent key allows for a multi-turn conversation within the hook context.
 - `wakeMode` optional (`now` | `next-heartbeat`): Whether to trigger an immediate heartbeat (default `now`) or wait for the next periodic check.
 - `deliver` optional (boolean): If `true`, the agent's response will be sent to the messaging channel. Defaults to `true`. Responses that are only heartbeat acknowledgments are automatically skipped.
-- `channel` optional (string): The messaging channel for delivery. One of: `last`, `whatsapp`, `telegram`, `discord`, `slack`, `signal`, `imessage`, `msteams`. Defaults to `last`.
-- `to` optional (string): The recipient identifier for the channel (e.g., phone number for WhatsApp/Signal, chat ID for Telegram, channel ID for Discord/Slack, conversation ID for MS Teams). Defaults to the last recipient in the main session.
+- `channel` optional (string): The messaging channel for delivery. One of: `last`, `whatsapp`, `telegram`, `discord`, `slack`, `mattermost`, `signal`, `imessage`, `msteams`. Defaults to `last`.
+- `to` optional (string): The recipient identifier for the channel (e.g., phone number for WhatsApp/Signal, chat ID for Telegram, channel ID for Discord/Slack/Mattermost, conversation ID for MS Teams). Defaults to the last recipient in the main session.
 - `model` optional (string): Model override (e.g., `anthropic/claude-3-5-sonnet` or an alias). Must be in the allowed model list if restricted.
 - `thinking` optional (string): Thinking level override (e.g., `low`, `medium`, `high`).
 - `timeoutSeconds` optional (number): Maximum duration for the agent run in seconds.
diff --git a/docs/channels/index.md b/docs/channels/index.md
index af1d5bfee..e7e012233 100644
--- a/docs/channels/index.md
+++ b/docs/channels/index.md
@@ -15,6 +15,7 @@ Text is supported everywhere; media and reactions vary by channel.
 - [Telegram](/channels/telegram) — Bot API via grammY; supports groups.
 - [Discord](/channels/discord) — Discord Bot API + Gateway; supports servers, channels, and DMs.
 - [Slack](/channels/slack) — Bolt SDK; workspace apps.
+- [Mattermost](/channels/mattermost) — Bot API + WebSocket; channels, groups, DMs.
 - [Signal](/channels/signal) — signal-cli; privacy-focused.
 - [BlueBubbles](/channels/bluebubbles) — **Recommended for iMessage**; uses the BlueBubbles macOS server REST API with full feature support (edit, unsend, effects, reactions, group management — edit currently broken on macOS 26 Tahoe).
 - [iMessage](/channels/imessage) — macOS only; native integration via imsg (legacy, consider BlueBubbles for new setups).
diff --git a/docs/channels/mattermost.md b/docs/channels/mattermost.md
new file mode 100644
index 000000000..c117de8cb
--- /dev/null
+++ b/docs/channels/mattermost.md
@@ -0,0 +1,87 @@
+---
+summary: "Mattermost bot setup and Clawdbot config"
+read_when:
+  - Setting up Mattermost
+  - Debugging Mattermost routing
+---
+
+# Mattermost
+
+## Quick setup
+1) Create a Mattermost bot account and copy the **bot token**.
+2) Copy the Mattermost **base URL** (e.g., `https://chat.example.com`).
+3) Configure Clawdbot and start the gateway.
+
+Minimal config:
+```json5
+{
+  channels: {
+    mattermost: {
+      enabled: true,
+      botToken: "mm-token",
+      baseUrl: "https://chat.example.com"
+    }
+  }
+}
+```
+
+## Environment variables (default account)
+Set these on the gateway host if you prefer env vars:
+
+- `MATTERMOST_BOT_TOKEN=...`
+- `MATTERMOST_URL=https://chat.example.com`
+
+Env vars apply only to the **default** account (`default`). Other accounts must use config values.
+
+## Chat modes
+Mattermost responds to DMs automatically. Channel behavior is controlled by `chatmode`:
+
+- `oncall` (default): respond only when @mentioned in channels.
+- `onmessage`: respond to every channel message.
+- `onchar`: respond when a message starts with a trigger prefix.
+
+Config example:
+```json5
+{
+  channels: {
+    mattermost: {
+      chatmode: "onchar",
+      oncharPrefixes: [">", "!"]
+    }
+  }
+}
+```
+
+Notes:
+- `onchar` still responds to explicit @mentions.
+- `channels.mattermost.requireMention` is honored for legacy configs but `chatmode` is preferred.
+
+## Targets for outbound delivery
+Use these target formats with `clawdbot message send` or cron/webhooks:
+
+- `channel:<id>` for a channel
+- `user:<id>` for a DM
+- `@username` for a DM (resolved via the Mattermost API)
+
+Bare IDs are treated as channels.
+
+## Multi-account
+Mattermost supports multiple accounts under `channels.mattermost.accounts`:
+
+```json5
+{
+  channels: {
+    mattermost: {
+      accounts: {
+        default: { name: "Primary", botToken: "mm-token", baseUrl: "https://chat.example.com" },
+        alerts: { name: "Alerts", botToken: "mm-token-2", baseUrl: "https://alerts.example.com" }
+      }
+    }
+  }
+}
+```
+
+## Troubleshooting
+- No replies in channels: ensure the bot is in the channel and mention it (oncall), use a trigger prefix (onchar), or set `chatmode: "onmessage"`.
+- Auth errors: check the bot token, base URL, and whether the account is enabled.
+- Multi-account issues: env vars only apply to the `default` account.
diff --git a/docs/cli/channels.md b/docs/cli/channels.md
index 55214ae63..fd74aabbd 100644
--- a/docs/cli/channels.md
+++ b/docs/cli/channels.md
@@ -1,7 +1,7 @@
 ---
 summary: "CLI reference for `clawdbot channels` (accounts, status, login/logout, logs)"
 read_when:
-  - You want to add/remove channel accounts (WhatsApp/Telegram/Discord/Slack/Signal/iMessage)
+  - You want to add/remove channel accounts (WhatsApp/Telegram/Discord/Slack/Mattermost/Signal/iMessage)
   - You want to check channel status or tail channel logs
 ---
 
diff --git a/docs/cli/index.md b/docs/cli/index.md
index d12b5e9f8..3b6d50f2b 100644
--- a/docs/cli/index.md
+++ b/docs/cli/index.md
@@ -370,7 +370,7 @@ Options:
 ## Channel helpers
 
 ### `channels`
-Manage chat channel accounts (WhatsApp/Telegram/Discord/Slack/Signal/iMessage/MS Teams).
+Manage chat channel accounts (WhatsApp/Telegram/Discord/Slack/Mattermost/Signal/iMessage/MS Teams).
 
 Subcommands:
 - `channels list`: show configured channels and auth profiles (Claude Code + Codex CLI OAuth sync included).
@@ -383,7 +383,7 @@ Subcommands:
 - `channels logout`: log out of a channel session (if supported).
 
 Common options:
-- `--channel <name>`: `whatsapp|telegram|discord|slack|signal|imessage|msteams`
+- `--channel <name>`: `whatsapp|telegram|discord|slack|mattermost|signal|imessage|msteams`
 - `--account <id>`: channel account id (default `default`)
 - `--name <label>`: display name for the account
 
@@ -490,7 +490,7 @@ Options:
 - `--session-id <id>`
 - `--thinking <off|minimal|low|medium|high|xhigh>` (GPT-5.2 + Codex models only)
 - `--verbose <on|full|off>`
-- `--channel <whatsapp|telegram|discord|slack|signal|imessage>`
+- `--channel <whatsapp|telegram|discord|slack|mattermost|signal|imessage|msteams>`
 - `--local`
 - `--deliver`
 - `--json`
diff --git a/docs/cli/message.md b/docs/cli/message.md
index 6baa73ebc..43d820665 100644
--- a/docs/cli/message.md
+++ b/docs/cli/message.md
@@ -8,7 +8,7 @@ read_when:
 # `clawdbot message`
 
 Single outbound command for sending messages and channel actions
-(Discord/Slack/Telegram/WhatsApp/Signal/iMessage/MS Teams).
+(Discord/Slack/Mattermost/Telegram/WhatsApp/Signal/iMessage/MS Teams).
 
 ## Usage
 
@@ -19,13 +19,14 @@ clawdbot message <subcommand> [flags]
 Channel selection:
 - `--channel` required if more than one channel is configured.
 - If exactly one channel is configured, it becomes the default.
-- Values: `whatsapp|telegram|discord|slack|signal|imessage|msteams`
+- Values: `whatsapp|telegram|discord|slack|mattermost|signal|imessage|msteams`
 
 Target formats (`--target`):
 - WhatsApp: E.164 or group JID
 - Telegram: chat id or `@username`
 - Discord: `channel:<id>` or `user:<id>` (or `<@id>` mention; raw numeric ids are treated as channels)
 - Slack: `channel:<id>` or `user:<id>` (raw channel id is accepted)
+- Mattermost: `channel:<id>`, `user:<id>`, or `@username` (bare ids are treated as channels)
 - Signal: `+E.164`, `group:<id>`, `signal:+E.164`, `signal:group:<id>`, or `username:<name>`/`u:<name>`
 - iMessage: handle, `chat_id:<id>`, `chat_guid:<guid>`, or `chat_identifier:<id>`
 - MS Teams: conversation id (`19:...@thread.tacv2`) or `conversation:<id>` or `user:<aad-object-id>`
@@ -49,7 +50,7 @@ Name lookup:
 ### Core
 
 - `send`
-  - Channels: WhatsApp/Telegram/Discord/Slack/Signal/iMessage/MS Teams
+  - Channels: WhatsApp/Telegram/Discord/Slack/Mattermost/Signal/iMessage/MS Teams
   - Required: `--target`, plus `--message` or `--media`
   - Optional: `--media`, `--reply-to`, `--thread-id`, `--gif-playback`
   - Telegram only: `--buttons` (requires `channels.telegram.capabilities.inlineButtons` to allow it)
diff --git a/docs/docs.json b/docs/docs.json
index 8b81228ab..88983fc47 100644
--- a/docs/docs.json
+++ b/docs/docs.json
@@ -133,6 +133,14 @@
       "source": "/message/",
       "destination": "/cli/message"
     },
+    {
+      "source": "/mattermost",
+      "destination": "/channels/mattermost"
+    },
+    {
+      "source": "/mattermost/",
+      "destination": "/channels/mattermost"
+    },
     {
       "source": "/providers/discord",
       "destination": "/channels/discord"
@@ -165,6 +173,14 @@
       "source": "/providers/location/",
       "destination": "/channels/location"
     },
+    {
+      "source": "/providers/mattermost",
+      "destination": "/channels/mattermost"
+    },
+    {
+      "source": "/providers/mattermost/",
+      "destination": "/channels/mattermost"
+    },
     {
       "source": "/providers/msteams",
       "destination": "/channels/msteams"
@@ -932,6 +948,7 @@
           "channels/grammy",
           "channels/discord",
           "channels/slack",
+          "channels/mattermost",
           "channels/signal",
           "channels/imessage",
           "channels/msteams",
diff --git a/docs/gateway/configuration.md b/docs/gateway/configuration.md
index 8ebcef47a..f83c4ab58 100644
--- a/docs/gateway/configuration.md
+++ b/docs/gateway/configuration.md
@@ -529,7 +529,7 @@ Notes:
 - Outbound commands default to account `default` if present; otherwise the first configured account id (sorted).
 - The legacy single-account Baileys auth dir is migrated by `clawdbot doctor` into `whatsapp/default`.
 
-### `channels.telegram.accounts` / `channels.discord.accounts` / `channels.slack.accounts` / `channels.signal.accounts` / `channels.imessage.accounts`
+### `channels.telegram.accounts` / `channels.discord.accounts` / `channels.slack.accounts` / `channels.mattermost.accounts` / `channels.signal.accounts` / `channels.imessage.accounts`
 
 Run multiple accounts per channel (each account has its own `accountId` and optional `name`):
 
@@ -1190,6 +1190,35 @@ Slack action groups (gate `slack` tool actions):
 | memberInfo | enabled | Member info |
 | emojiList | enabled | Custom emoji list |
 
+### `channels.mattermost` (bot token)
+
+Mattermost requires a bot token plus the base URL for your server:
+
+```json5
+{
+  channels: {
+    mattermost: {
+      enabled: true,
+      botToken: "mm-token",
+      baseUrl: "https://chat.example.com",
+      chatmode: "oncall", // oncall | onmessage | onchar
+      oncharPrefixes: [">", "!"],
+      textChunkLimit: 4000
+    }
+  }
+}
+```
+
+Clawdbot starts Mattermost when the account is configured (bot token + base URL) and enabled. The token + base URL are resolved from `channels.mattermost.botToken` + `channels.mattermost.baseUrl` or `MATTERMOST_BOT_TOKEN` + `MATTERMOST_URL` for the default account (unless `channels.mattermost.enabled` is `false`).
+
+Chat modes:
+- `oncall` (default): respond to channel messages only when @mentioned.
+- `onmessage`: respond to every channel message.
+- `onchar`: respond when a message starts with a trigger prefix (`channels.mattermost.oncharPrefixes`, default `[">", "!"]`).
+
+Multi-account support lives under `channels.mattermost.accounts` (see the multi-account section above). Env vars only apply to the default account.
+Use `channel:<id>` or `user:<id>` (or `@username`) when specifying delivery targets; bare ids are treated as channel ids.
+
 ### `channels.signal` (signal-cli)
 
 Signal reactions can emit system events (shared reaction tooling):
@@ -1709,8 +1738,9 @@ Block streaming:
   with `maxChars` capped to the channel text limit. Signal/Slack/Discord default
   to `minChars: 1500` unless overridden.
   Channel overrides: `channels.whatsapp.blockStreamingCoalesce`, `channels.telegram.blockStreamingCoalesce`,
-  `channels.discord.blockStreamingCoalesce`, `channels.slack.blockStreamingCoalesce`, `channels.signal.blockStreamingCoalesce`,
-  `channels.imessage.blockStreamingCoalesce`, `channels.msteams.blockStreamingCoalesce` (and per-account variants).
+  `channels.discord.blockStreamingCoalesce`, `channels.slack.blockStreamingCoalesce`, `channels.mattermost.blockStreamingCoalesce`,
+  `channels.signal.blockStreamingCoalesce`, `channels.imessage.blockStreamingCoalesce`, `channels.msteams.blockStreamingCoalesce`
+  (and per-account variants).
 - `agents.defaults.humanDelay`: randomized pause between **block replies** after the first.
   Modes: `off` (default), `natural` (800–2500ms), `custom` (use `minMs`/`maxMs`).
   Per-agent override: `agents.list[].humanDelay`.
diff --git a/docs/index.md b/docs/index.md
index 293609031..6aa9ef5eb 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -12,7 +12,7 @@ read_when:
 </p>
 
 <p align="center">
-  <strong>Any OS + WhatsApp/Telegram/Discord/iMessage gateway for AI agents (Pi).</strong><br />
+  <strong>Any OS + WhatsApp/Telegram/Discord/Mattermost/iMessage gateway for AI agents (Pi).</strong><br />
   Send a message, get an agent response — from your pocket.
 </p>
 
@@ -23,7 +23,7 @@ read_when:
   <a href="/start/clawd">Clawdbot assistant setup</a>
 </p>
 
-Clawdbot bridges WhatsApp (via WhatsApp Web / Baileys), Telegram (Bot API / grammY), Discord (Bot API / channels.discord.js), and iMessage (imsg CLI) to coding agents like [Pi](https://github.com/badlogic/pi-mono).
+Clawdbot bridges WhatsApp (via WhatsApp Web / Baileys), Telegram (Bot API / grammY), Discord (Bot API / channels.discord.js), Mattermost (Bot API + WebSocket), and iMessage (imsg CLI) to coding agents like [Pi](https://github.com/badlogic/pi-mono).
 Clawdbot also powers [Clawd](https://clawd.me), the space‑lobster assistant.
 
 ## Start here
@@ -44,7 +44,7 @@ Remote access: [Web surfaces](/web) and [Tailscale](/gateway/tailscale)
 ## How it works
 
 ```
-WhatsApp / Telegram / Discord
+WhatsApp / Telegram / Discord / Mattermost
         │
         ▼
   ┌───────────────────────────┐
@@ -79,6 +79,7 @@ Most operations flow through the **Gateway** (`clawdbot gateway`), a single long
 - 📱 **WhatsApp Integration** — Uses Baileys for WhatsApp Web protocol
 - ✈️ **Telegram Bot** — DMs + groups via grammY
 - 🎮 **Discord Bot** — DMs + guild channels via channels.discord.js
+- 🧩 **Mattermost Bot** — Bot token + WebSocket events
 - 💬 **iMessage** — Local imsg CLI integration (macOS)
 - 🤖 **Agent bridge** — Pi (RPC mode) with tool streaming
 - ⏱️ **Streaming + chunking** — Block streaming + Telegram draft streaming details ([/concepts/streaming](/concepts/streaming))
@@ -190,6 +191,7 @@ Example:
   - [Control UI (browser)](/web/control-ui)
   - [Telegram](/channels/telegram)
   - [Discord](/channels/discord)
+  - [Mattermost](/channels/mattermost)
   - [iMessage](/channels/imessage)
   - [Groups](/concepts/groups)
   - [WhatsApp group messages](/concepts/group-messages)
diff --git a/docs/providers/index.md b/docs/providers/index.md
index 7a4e9633b..983dd860f 100644
--- a/docs/providers/index.md
+++ b/docs/providers/index.md
@@ -9,7 +9,7 @@ read_when:
 Clawdbot can use many LLM providers. Pick a provider, authenticate, then set the
 default model as `provider/model`.
 
-Looking for chat channel docs (WhatsApp/Telegram/Discord/Slack/etc.)? See [Channels](/channels).
+Looking for chat channel docs (WhatsApp/Telegram/Discord/Slack/Mattermost/etc.)? See [Channels](/channels).
 
 ## Quick start
 
diff --git a/docs/start/clawd.md b/docs/start/clawd.md
index 0ea039cc2..b68bdee7c 100644
--- a/docs/start/clawd.md
+++ b/docs/start/clawd.md
@@ -6,14 +6,14 @@ read_when:
 ---
 # Building a personal assistant with Clawdbot (Clawd-style)
 
-Clawdbot is a WhatsApp + Telegram + Discord gateway for **Pi** agents. This guide is the “personal assistant” setup: one dedicated WhatsApp number that behaves like your always-on agent.
+Clawdbot is a WhatsApp + Telegram + Discord + Mattermost gateway for **Pi** agents. This guide is the "personal assistant" setup: one dedicated WhatsApp number that behaves like your always-on agent.
 
 ## ⚠️ Safety first
 
 You’re putting an agent in a position to:
 - run commands on your machine (depending on your Pi tool setup)
 - read/write files in your workspace
-- send messages back out via WhatsApp/Telegram/Discord
+- send messages back out via WhatsApp/Telegram/Discord/Mattermost
 
 Start conservative:
 - Always set `channels.whatsapp.allowFrom` (never run open-to-the-world on your personal Mac).
diff --git a/docs/start/faq.md b/docs/start/faq.md
index f62e0315f..a79d193fc 100644
--- a/docs/start/faq.md
+++ b/docs/start/faq.md
@@ -175,7 +175,7 @@ Quick answers plus deeper troubleshooting for real-world setups (local dev, VPS,
 
 ### What is Clawdbot, in one paragraph?
 
-Clawdbot is a personal AI assistant you run on your own devices. It replies on the messaging surfaces you already use (WhatsApp, Telegram, Slack, Discord, Signal, iMessage, WebChat) and can also do voice + a live Canvas on supported platforms. The **Gateway** is the always‑on control plane; the assistant is the product.
+Clawdbot is a personal AI assistant you run on your own devices. It replies on the messaging surfaces you already use (WhatsApp, Telegram, Slack, Mattermost, Discord, Signal, iMessage, WebChat) and can also do voice + a live Canvas on supported platforms. The **Gateway** is the always-on control plane; the assistant is the product.
 
 ## Quick start and first-run setup
 
@@ -232,7 +232,7 @@ Node **>= 22** is required. `pnpm` is recommended. Bun is **not recommended** fo
 - **Model/auth setup** (Anthropic **setup-token** recommended for Claude subscriptions, OpenAI Codex OAuth supported, API keys optional, LM Studio local models supported)
 - **Workspace** location + bootstrap files
 - **Gateway settings** (bind/port/auth/tailscale)
-- **Providers** (WhatsApp, Telegram, Discord, Signal, iMessage)
+- **Providers** (WhatsApp, Telegram, Discord, Mattermost, Signal, iMessage)
 - **Daemon install** (LaunchAgent on macOS; systemd user unit on Linux/WSL2)
 - **Health checks** and **skills** selection
 
@@ -360,7 +360,7 @@ lowest friction and you’re okay with sleep/restarts, run it locally.
 - **Pros:** always‑on, stable network, no laptop sleep issues, easier to keep running.
 - **Cons:** often run headless (use screenshots), remote file access only, you must SSH for updates.
 
-**Clawdbot‑specific note:** WhatsApp/Telegram/Slack/Discord all work fine from a VPS. The only real trade‑off is **headless browser** vs a visible window. See [Browser](/tools/browser).
+**Clawdbot-specific note:** WhatsApp/Telegram/Slack/Mattermost/Discord all work fine from a VPS. The only real trade-off is **headless browser** vs a visible window. See [Browser](/tools/browser).
 
 **Recommended default:** VPS if you had gateway disconnects before. Local is great when you’re actively using the Mac and want local file access or UI automation with a visible browser.
 
diff --git a/docs/start/getting-started.md b/docs/start/getting-started.md
index aa890eac5..5af3b7a8e 100644
--- a/docs/start/getting-started.md
+++ b/docs/start/getting-started.md
@@ -12,7 +12,7 @@ Goal: go from **zero** → **first working chat** (with sane defaults) as quickl
 Recommended path: use the **CLI onboarding wizard** (`clawdbot onboard`). It sets up:
 - model/auth (OAuth recommended)
 - gateway settings
-- channels (WhatsApp/Telegram/Discord/…)
+- channels (WhatsApp/Telegram/Discord/Mattermost/...)
 - pairing defaults (secure DMs)
 - workspace bootstrap + skills
 - optional background daemon
@@ -80,7 +80,7 @@ clawdbot onboard --install-daemon
 What you’ll choose:
 - **Local vs Remote** gateway
 - **Auth**: OpenAI Code (Codex) subscription (OAuth) or API keys. For Anthropic we recommend an API key; `claude setup-token` is also supported.
-- **Providers**: WhatsApp QR login, Telegram/Discord bot tokens, etc.
+- **Providers**: WhatsApp QR login, Telegram/Discord/Mattermost bot tokens, etc.
 - **Daemon**: background install (launchd/systemd; WSL2 uses systemd)
   - **Runtime**: Node (recommended; required for WhatsApp/Telegram). Bun is **not recommended**.
 - **Gateway token**: the wizard generates one by default (even on loopback) and stores it in `gateway.auth.token`.
@@ -140,6 +140,7 @@ WhatsApp doc: [WhatsApp](/channels/whatsapp)
 The wizard can write tokens/config for you. If you prefer manual config, start with:
 - Telegram: [Telegram](/channels/telegram)
 - Discord: [Discord](/channels/discord)
+- Mattermost: [Mattermost](/channels/mattermost)
 
 **Telegram DM tip:** your first DM returns a pairing code. Approve it (see next step) or the bot won’t respond.
 
diff --git a/docs/start/hubs.md b/docs/start/hubs.md
index 346178b2b..ee279fc4e 100644
--- a/docs/start/hubs.md
+++ b/docs/start/hubs.md
@@ -67,6 +67,7 @@ Use these hubs to discover every page, including deep dives and reference docs t
 - [Telegram (grammY notes)](/channels/grammy)
 - [Slack](/channels/slack)
 - [Discord](/channels/discord)
+- [Mattermost](/channels/mattermost)
 - [Signal](/channels/signal)
 - [iMessage](/channels/imessage)
 - [Location parsing](/channels/location)
diff --git a/docs/start/wizard.md b/docs/start/wizard.md
index 8be09ca31..f67ce682b 100644
--- a/docs/start/wizard.md
+++ b/docs/start/wizard.md
@@ -48,7 +48,7 @@ The wizard starts with **QuickStart** (defaults) vs **Advanced** (full control).
   - Model/auth (OpenAI Code (Codex) subscription OAuth, Anthropic API key (recommended) or `claude setup-token`, plus MiniMax/GLM/Moonshot/AI Gateway options)
 - Workspace location + bootstrap files
 - Gateway settings (port/bind/auth/tailscale)
-- Providers (Telegram, WhatsApp, Discord, Signal)
+- Providers (Telegram, WhatsApp, Discord, Mattermost, Signal)
 - Daemon install (LaunchAgent / systemd user unit)
 - Health check
 - Skills (recommended)
@@ -118,6 +118,7 @@ Tip: `--json` does **not** imply non-interactive mode. Use `--non-interactive` (
    - WhatsApp: optional QR login.
    - Telegram: bot token.
    - Discord: bot token.
+   - Mattermost: bot token + base URL.
    - Signal: optional `signal-cli` install + account config.
    - iMessage: local `imsg` CLI path + DB access.
   - DM security: default is pairing. First DM sends a code; approve via `clawdbot pairing approve <channel> <code>` or use allowlists.
diff --git a/docs/web/control-ui.md b/docs/web/control-ui.md
index b1102c47d..5786c696e 100644
--- a/docs/web/control-ui.md
+++ b/docs/web/control-ui.md
@@ -30,7 +30,7 @@ The onboarding wizard generates a gateway token by default, so paste it here on
 ## What it can do (today)
 - Chat with the model via Gateway WS (`chat.history`, `chat.send`, `chat.abort`, `chat.inject`)
 - Stream tool calls + live tool output cards in Chat (agent events)
-- Channels: WhatsApp/Telegram status + QR login + per-channel config (`channels.status`, `web.login.*`, `config.patch`)
+- Channels: WhatsApp/Telegram/Discord/Slack/Mattermost status + QR login + per-channel config (`channels.status`, `web.login.*`, `config.patch`)
 - Instances: presence list + refresh (`system-presence`)
 - Sessions: list + per-session thinking/verbose overrides (`sessions.list`, `sessions.patch`)
 - Cron jobs: list/add/run/enable/disable + run history (`cron.*`)
diff --git a/extensions/mattermost/clawdbot.plugin.json b/extensions/mattermost/clawdbot.plugin.json
new file mode 100644
index 000000000..ddb3f8160
--- /dev/null
+++ b/extensions/mattermost/clawdbot.plugin.json
@@ -0,0 +1,11 @@
+{
+  "id": "mattermost",
+  "channels": [
+    "mattermost"
+  ],
+  "configSchema": {
+    "type": "object",
+    "additionalProperties": false,
+    "properties": {}
+  }
+}
diff --git a/extensions/mattermost/index.ts b/extensions/mattermost/index.ts
new file mode 100644
index 000000000..f3bf17ad5
--- /dev/null
+++ b/extensions/mattermost/index.ts
@@ -0,0 +1,18 @@
+import type { ClawdbotPluginApi } from "clawdbot/plugin-sdk";
+import { emptyPluginConfigSchema } from "clawdbot/plugin-sdk";
+
+import { mattermostPlugin } from "./src/channel.js";
+import { setMattermostRuntime } from "./src/runtime.js";
+
+const plugin = {
+  id: "mattermost",
+  name: "Mattermost",
+  description: "Mattermost channel plugin",
+  configSchema: emptyPluginConfigSchema(),
+  register(api: ClawdbotPluginApi) {
+    setMattermostRuntime(api.runtime);
+    api.registerChannel({ plugin: mattermostPlugin });
+  },
+};
+
+export default plugin;
diff --git a/extensions/mattermost/package.json b/extensions/mattermost/package.json
new file mode 100644
index 000000000..8ba462f45
--- /dev/null
+++ b/extensions/mattermost/package.json
@@ -0,0 +1,11 @@
+{
+  "name": "@clawdbot/mattermost",
+  "version": "2026.1.20-2",
+  "type": "module",
+  "description": "Clawdbot Mattermost channel plugin",
+  "clawdbot": {
+    "extensions": [
+      "./index.ts"
+    ]
+  }
+}
diff --git a/extensions/mattermost/src/channel.ts b/extensions/mattermost/src/channel.ts
new file mode 100644
index 000000000..840772a17
--- /dev/null
+++ b/extensions/mattermost/src/channel.ts
@@ -0,0 +1,270 @@
+import {
+  applyAccountNameToChannelSection,
+  buildChannelConfigSchema,
+  DEFAULT_ACCOUNT_ID,
+  deleteAccountFromConfigSection,
+  getChatChannelMeta,
+  listMattermostAccountIds,
+  looksLikeMattermostTargetId,
+  migrateBaseNameToDefaultAccount,
+  normalizeAccountId,
+  normalizeMattermostBaseUrl,
+  normalizeMattermostMessagingTarget,
+  resolveDefaultMattermostAccountId,
+  resolveMattermostAccount,
+  resolveMattermostGroupRequireMention,
+  setAccountEnabledInConfigSection,
+  mattermostOnboardingAdapter,
+  MattermostConfigSchema,
+  type ChannelPlugin,
+  type ResolvedMattermostAccount,
+} from "clawdbot/plugin-sdk";
+
+import { getMattermostRuntime } from "./runtime.js";
+
+const meta = getChatChannelMeta("mattermost");
+
+export const mattermostPlugin: ChannelPlugin<ResolvedMattermostAccount> = {
+  id: "mattermost",
+  meta: {
+    ...meta,
+  },
+  onboarding: mattermostOnboardingAdapter,
+  capabilities: {
+    chatTypes: ["direct", "channel", "group", "thread"],
+    threads: true,
+    media: true,
+  },
+  streaming: {
+    blockStreamingCoalesceDefaults: { minChars: 1500, idleMs: 1000 },
+  },
+  reload: { configPrefixes: ["channels.mattermost"] },
+  configSchema: buildChannelConfigSchema(MattermostConfigSchema),
+  config: {
+    listAccountIds: (cfg) => listMattermostAccountIds(cfg),
+    resolveAccount: (cfg, accountId) => resolveMattermostAccount({ cfg, accountId }),
+    defaultAccountId: (cfg) => resolveDefaultMattermostAccountId(cfg),
+    setAccountEnabled: ({ cfg, accountId, enabled }) =>
+      setAccountEnabledInConfigSection({
+        cfg,
+        sectionKey: "mattermost",
+        accountId,
+        enabled,
+        allowTopLevel: true,
+      }),
+    deleteAccount: ({ cfg, accountId }) =>
+      deleteAccountFromConfigSection({
+        cfg,
+        sectionKey: "mattermost",
+        accountId,
+        clearBaseFields: ["botToken", "baseUrl", "name"],
+      }),
+    isConfigured: (account) => Boolean(account.botToken && account.baseUrl),
+    describeAccount: (account) => ({
+      accountId: account.accountId,
+      name: account.name,
+      enabled: account.enabled,
+      configured: Boolean(account.botToken && account.baseUrl),
+      botTokenSource: account.botTokenSource,
+      baseUrl: account.baseUrl,
+    }),
+  },
+  groups: {
+    resolveRequireMention: resolveMattermostGroupRequireMention,
+  },
+  messaging: {
+    normalizeTarget: normalizeMattermostMessagingTarget,
+    targetResolver: {
+      looksLikeId: looksLikeMattermostTargetId,
+      hint: "<channelId|user:ID|channel:ID>",
+    },
+  },
+  outbound: {
+    deliveryMode: "direct",
+    chunker: (text, limit) => getMattermostRuntime().channel.text.chunkMarkdownText(text, limit),
+    textChunkLimit: 4000,
+    resolveTarget: ({ to }) => {
+      const trimmed = to?.trim();
+      if (!trimmed) {
+        return {
+          ok: false,
+          error: new Error(
+            "Delivering to Mattermost requires --to <channelId|user:ID|channel:ID>",
+          ),
+        };
+      }
+      return { ok: true, to: trimmed };
+    },
+    sendText: async ({ to, text, accountId, deps, replyToId }) => {
+      const send =
+        deps?.sendMattermost ?? getMattermostRuntime().channel.mattermost.sendMessageMattermost;
+      const result = await send(to, text, {
+        accountId: accountId ?? undefined,
+        replyToId: replyToId ?? undefined,
+      });
+      return { channel: "mattermost", ...result };
+    },
+    sendMedia: async ({ to, text, mediaUrl, accountId, deps, replyToId }) => {
+      const send =
+        deps?.sendMattermost ?? getMattermostRuntime().channel.mattermost.sendMessageMattermost;
+      const result = await send(to, text, {
+        accountId: accountId ?? undefined,
+        mediaUrl,
+        replyToId: replyToId ?? undefined,
+      });
+      return { channel: "mattermost", ...result };
+    },
+  },
+  status: {
+    defaultRuntime: {
+      accountId: DEFAULT_ACCOUNT_ID,
+      running: false,
+      connected: false,
+      lastConnectedAt: null,
+      lastDisconnect: null,
+      lastStartAt: null,
+      lastStopAt: null,
+      lastError: null,
+    },
+    buildChannelSummary: ({ snapshot }) => ({
+      configured: snapshot.configured ?? false,
+      botTokenSource: snapshot.botTokenSource ?? "none",
+      running: snapshot.running ?? false,
+      connected: snapshot.connected ?? false,
+      lastStartAt: snapshot.lastStartAt ?? null,
+      lastStopAt: snapshot.lastStopAt ?? null,
+      lastError: snapshot.lastError ?? null,
+      baseUrl: snapshot.baseUrl ?? null,
+      probe: snapshot.probe,
+      lastProbeAt: snapshot.lastProbeAt ?? null,
+    }),
+    probeAccount: async ({ account, timeoutMs }) => {
+      const token = account.botToken?.trim();
+      const baseUrl = account.baseUrl?.trim();
+      if (!token || !baseUrl) {
+        return { ok: false, error: "bot token or baseUrl missing" };
+      }
+      return await getMattermostRuntime().channel.mattermost.probeMattermost(
+        baseUrl,
+        token,
+        timeoutMs,
+      );
+    },
+    buildAccountSnapshot: ({ account, runtime, probe }) => ({
+      accountId: account.accountId,
+      name: account.name,
+      enabled: account.enabled,
+      configured: Boolean(account.botToken && account.baseUrl),
+      botTokenSource: account.botTokenSource,
+      baseUrl: account.baseUrl,
+      running: runtime?.running ?? false,
+      connected: runtime?.connected ?? false,
+      lastConnectedAt: runtime?.lastConnectedAt ?? null,
+      lastDisconnect: runtime?.lastDisconnect ?? null,
+      lastStartAt: runtime?.lastStartAt ?? null,
+      lastStopAt: runtime?.lastStopAt ?? null,
+      lastError: runtime?.lastError ?? null,
+      probe,
+      lastInboundAt: runtime?.lastInboundAt ?? null,
+      lastOutboundAt: runtime?.lastOutboundAt ?? null,
+    }),
+  },
+  setup: {
+    resolveAccountId: ({ accountId }) => normalizeAccountId(accountId),
+    applyAccountName: ({ cfg, accountId, name }) =>
+      applyAccountNameToChannelSection({
+        cfg,
+        channelKey: "mattermost",
+        accountId,
+        name,
+      }),
+    validateInput: ({ accountId, input }) => {
+      if (input.useEnv && accountId !== DEFAULT_ACCOUNT_ID) {
+        return "Mattermost env vars can only be used for the default account.";
+      }
+      const token = input.botToken ?? input.token;
+      const baseUrl = input.httpUrl;
+      if (!input.useEnv && (!token || !baseUrl)) {
+        return "Mattermost requires --bot-token and --http-url (or --use-env).";
+      }
+      if (baseUrl && !normalizeMattermostBaseUrl(baseUrl)) {
+        return "Mattermost --http-url must include a valid base URL.";
+      }
+      return null;
+    },
+    applyAccountConfig: ({ cfg, accountId, input }) => {
+      const token = input.botToken ?? input.token;
+      const baseUrl = input.httpUrl?.trim();
+      const namedConfig = applyAccountNameToChannelSection({
+        cfg,
+        channelKey: "mattermost",
+        accountId,
+        name: input.name,
+      });
+      const next =
+        accountId !== DEFAULT_ACCOUNT_ID
+          ? migrateBaseNameToDefaultAccount({
+              cfg: namedConfig,
+              channelKey: "mattermost",
+            })
+          : namedConfig;
+      if (accountId === DEFAULT_ACCOUNT_ID) {
+        return {
+          ...next,
+          channels: {
+            ...next.channels,
+            mattermost: {
+              ...next.channels?.mattermost,
+              enabled: true,
+              ...(input.useEnv
+                ? {}
+                : {
+                    ...(token ? { botToken: token } : {}),
+                    ...(baseUrl ? { baseUrl } : {}),
+                  }),
+            },
+          },
+        };
+      }
+      return {
+        ...next,
+        channels: {
+          ...next.channels,
+          mattermost: {
+            ...next.channels?.mattermost,
+            enabled: true,
+            accounts: {
+              ...next.channels?.mattermost?.accounts,
+              [accountId]: {
+                ...next.channels?.mattermost?.accounts?.[accountId],
+                enabled: true,
+                ...(token ? { botToken: token } : {}),
+                ...(baseUrl ? { baseUrl } : {}),
+              },
+            },
+          },
+        },
+      };
+    },
+  },
+  gateway: {
+    startAccount: async (ctx) => {
+      const account = ctx.account;
+      ctx.setStatus({
+        accountId: account.accountId,
+        baseUrl: account.baseUrl,
+        botTokenSource: account.botTokenSource,
+      });
+      ctx.log?.info(`[${account.accountId}] starting channel`);
+      return getMattermostRuntime().channel.mattermost.monitorMattermostProvider({
+        botToken: account.botToken ?? undefined,
+        baseUrl: account.baseUrl ?? undefined,
+        accountId: account.accountId,
+        config: ctx.cfg,
+        runtime: ctx.runtime,
+        abortSignal: ctx.abortSignal,
+        statusSink: (patch) => ctx.setStatus({ accountId: ctx.accountId, ...patch }),
+      });
+    },
+  },
+};
diff --git a/extensions/mattermost/src/runtime.ts b/extensions/mattermost/src/runtime.ts
new file mode 100644
index 000000000..3d0ad283f
--- /dev/null
+++ b/extensions/mattermost/src/runtime.ts
@@ -0,0 +1,14 @@
+import type { PluginRuntime } from "clawdbot/plugin-sdk";
+
+let runtime: PluginRuntime | null = null;
+
+export function setMattermostRuntime(next: PluginRuntime) {
+  runtime = next;
+}
+
+export function getMattermostRuntime(): PluginRuntime {
+  if (!runtime) {
+    throw new Error("Mattermost runtime not initialized");
+  }
+  return runtime;
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index c0830488b..7c2c788b2 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -324,6 +324,8 @@ importers:
         specifier: ^11.10.6
         version: 11.10.6
 
+  extensions/mattermost: {}
+
   extensions/memory-core:
     dependencies:
       clawdbot:
diff --git a/src/auto-reply/reply/get-reply-run.ts b/src/auto-reply/reply/get-reply-run.ts
index aa2281de6..5a5e1b4e1 100644
--- a/src/auto-reply/reply/get-reply-run.ts
+++ b/src/auto-reply/reply/get-reply-run.ts
@@ -157,7 +157,10 @@ export async function runPreparedReply(
 
   const isFirstTurnInSession = isNewSession || !currentSystemSent;
   const isGroupChat = sessionCtx.ChatType === "group";
-  const wasMentioned = ctx.WasMentioned === true;
+  const originatingChannel =
+    (ctx.OriginatingChannel ?? ctx.Surface ?? ctx.Provider)?.toString().toLowerCase() ?? "";
+  const wasMentioned =
+    ctx.WasMentioned === true || (originatingChannel === "mattermost" && isGroupChat);
   const isHeartbeat = opts?.isHeartbeat === true;
   const typingMode = resolveTypingMode({
     configured: sessionCfg?.typingMode ?? agentCfg?.typingMode,
diff --git a/src/channels/dock.ts b/src/channels/dock.ts
index 92199a0f2..e6fd3150a 100644
--- a/src/channels/dock.ts
+++ b/src/channels/dock.ts
@@ -11,6 +11,7 @@ import { requireActivePluginRegistry } from "../plugins/runtime.js";
 import {
   resolveDiscordGroupRequireMention,
   resolveIMessageGroupRequireMention,
+  resolveMattermostGroupRequireMention,
   resolveSlackGroupRequireMention,
   resolveTelegramGroupRequireMention,
   resolveWhatsAppGroupRequireMention,
@@ -235,6 +236,30 @@ const DOCKS: Record<ChatChannelId, ChannelDock> = {
       },
     },
   },
+  mattermost: {
+    id: "mattermost",
+    capabilities: {
+      chatTypes: ["direct", "channel", "group", "thread"],
+      media: true,
+      threads: true,
+    },
+    outbound: { textChunkLimit: 4000 },
+    streaming: {
+      blockStreamingCoalesceDefaults: { minChars: 1500, idleMs: 1000 },
+    },
+    groups: {
+      resolveRequireMention: resolveMattermostGroupRequireMention,
+    },
+    threading: {
+      buildToolContext: ({ context, hasRepliedRef }) => ({
+        currentChannelId: context.To?.startsWith("channel:")
+          ? context.To.slice("channel:".length)
+          : undefined,
+        currentThreadTs: context.ReplyToId,
+        hasRepliedRef,
+      }),
+    },
+  },
   signal: {
     id: "signal",
     capabilities: {
diff --git a/src/channels/plugins/group-mentions.ts b/src/channels/plugins/group-mentions.ts
index 79dfa0320..bb7a111e8 100644
--- a/src/channels/plugins/group-mentions.ts
+++ b/src/channels/plugins/group-mentions.ts
@@ -1,6 +1,7 @@
 import type { ClawdbotConfig } from "../../config/config.js";
 import { resolveChannelGroupRequireMention } from "../../config/group-policy.js";
 import type { DiscordConfig } from "../../config/types.js";
+import { resolveMattermostAccount } from "../../mattermost/accounts.js";
 import { resolveSlackAccount } from "../../slack/accounts.js";
 
 type GroupMentionParams = {
@@ -184,6 +185,15 @@ export function resolveSlackGroupRequireMention(params: GroupMentionParams): boo
   return true;
 }
 
+export function resolveMattermostGroupRequireMention(params: GroupMentionParams): boolean {
+  const account = resolveMattermostAccount({
+    cfg: params.cfg,
+    accountId: params.accountId,
+  });
+  if (typeof account.requireMention === "boolean") return account.requireMention;
+  return true;
+}
+
 export function resolveBlueBubblesGroupRequireMention(params: GroupMentionParams): boolean {
   return resolveChannelGroupRequireMention({
     cfg: params.cfg,
diff --git a/src/channels/plugins/normalize/mattermost.ts b/src/channels/plugins/normalize/mattermost.ts
new file mode 100644
index 000000000..80366420f
--- /dev/null
+++ b/src/channels/plugins/normalize/mattermost.ts
@@ -0,0 +1,38 @@
+export function normalizeMattermostMessagingTarget(raw: string): string | undefined {
+  const trimmed = raw.trim();
+  if (!trimmed) return undefined;
+  const lower = trimmed.toLowerCase();
+  if (lower.startsWith("channel:")) {
+    const id = trimmed.slice("channel:".length).trim();
+    return id ? `channel:${id}` : undefined;
+  }
+  if (lower.startsWith("group:")) {
+    const id = trimmed.slice("group:".length).trim();
+    return id ? `channel:${id}` : undefined;
+  }
+  if (lower.startsWith("user:")) {
+    const id = trimmed.slice("user:".length).trim();
+    return id ? `user:${id}` : undefined;
+  }
+  if (lower.startsWith("mattermost:")) {
+    const id = trimmed.slice("mattermost:".length).trim();
+    return id ? `user:${id}` : undefined;
+  }
+  if (trimmed.startsWith("@")) {
+    const id = trimmed.slice(1).trim();
+    return id ? `user:${id}` : undefined;
+  }
+  if (trimmed.startsWith("#")) {
+    const id = trimmed.slice(1).trim();
+    return id ? `channel:${id}` : undefined;
+  }
+  return `channel:${trimmed}`;
+}
+
+export function looksLikeMattermostTargetId(raw: string): boolean {
+  const trimmed = raw.trim();
+  if (!trimmed) return false;
+  if (/^(user|channel|group|mattermost):/i.test(trimmed)) return true;
+  if (/^[@#]/.test(trimmed)) return true;
+  return /^[a-z0-9]{8,}$/i.test(trimmed);
+}
diff --git a/src/channels/plugins/onboarding/mattermost.ts b/src/channels/plugins/onboarding/mattermost.ts
new file mode 100644
index 000000000..3c7ffe2db
--- /dev/null
+++ b/src/channels/plugins/onboarding/mattermost.ts
@@ -0,0 +1,189 @@
+import type { ClawdbotConfig } from "../../../config/config.js";
+import {
+  listMattermostAccountIds,
+  resolveDefaultMattermostAccountId,
+  resolveMattermostAccount,
+} from "../../../mattermost/accounts.js";
+import { DEFAULT_ACCOUNT_ID, normalizeAccountId } from "../../../routing/session-key.js";
+import { formatDocsLink } from "../../../terminal/links.js";
+import type { WizardPrompter } from "../../../wizard/prompts.js";
+import type { ChannelOnboardingAdapter } from "../onboarding-types.js";
+import { promptAccountId } from "./helpers.js";
+
+const channel = "mattermost" as const;
+
+async function noteMattermostSetup(prompter: WizardPrompter): Promise<void> {
+  await prompter.note(
+    [
+      "1) Mattermost System Console -> Integrations -> Bot Accounts",
+      "2) Create a bot + copy its token",
+      "3) Use your server base URL (e.g., https://chat.example.com)",
+      "Tip: the bot must be a member of any channel you want it to monitor.",
+      `Docs: ${formatDocsLink("/channels/mattermost", "mattermost")}`,
+    ].join("\n"),
+    "Mattermost bot token",
+  );
+}
+
+export const mattermostOnboardingAdapter: ChannelOnboardingAdapter = {
+  channel,
+  getStatus: async ({ cfg }) => {
+    const configured = listMattermostAccountIds(cfg).some((accountId) => {
+      const account = resolveMattermostAccount({ cfg, accountId });
+      return Boolean(account.botToken && account.baseUrl);
+    });
+    return {
+      channel,
+      configured,
+      statusLines: [`Mattermost: ${configured ? "configured" : "needs token + url"}`],
+      selectionHint: configured ? "configured" : "needs setup",
+      quickstartScore: configured ? 2 : 1,
+    };
+  },
+  configure: async ({ cfg, prompter, accountOverrides, shouldPromptAccountIds }) => {
+    const override = accountOverrides.mattermost?.trim();
+    const defaultAccountId = resolveDefaultMattermostAccountId(cfg);
+    let accountId = override ? normalizeAccountId(override) : defaultAccountId;
+    if (shouldPromptAccountIds && !override) {
+      accountId = await promptAccountId({
+        cfg,
+        prompter,
+        label: "Mattermost",
+        currentId: accountId,
+        listAccountIds: listMattermostAccountIds,
+        defaultAccountId,
+      });
+    }
+
+    let next = cfg;
+    const resolvedAccount = resolveMattermostAccount({
+      cfg: next,
+      accountId,
+    });
+    const accountConfigured = Boolean(resolvedAccount.botToken && resolvedAccount.baseUrl);
+    const allowEnv = accountId === DEFAULT_ACCOUNT_ID;
+    const canUseEnv =
+      allowEnv &&
+      Boolean(process.env.MATTERMOST_BOT_TOKEN?.trim()) &&
+      Boolean(process.env.MATTERMOST_URL?.trim());
+    const hasConfigValues =
+      Boolean(resolvedAccount.config.botToken) || Boolean(resolvedAccount.config.baseUrl);
+
+    let botToken: string | null = null;
+    let baseUrl: string | null = null;
+
+    if (!accountConfigured) {
+      await noteMattermostSetup(prompter);
+    }
+
+    if (canUseEnv && !hasConfigValues) {
+      const keepEnv = await prompter.confirm({
+        message: "MATTERMOST_BOT_TOKEN + MATTERMOST_URL detected. Use env vars?",
+        initialValue: true,
+      });
+      if (keepEnv) {
+        next = {
+          ...next,
+          channels: {
+            ...next.channels,
+            mattermost: {
+              ...next.channels?.mattermost,
+              enabled: true,
+            },
+          },
+        };
+      } else {
+        botToken = String(
+          await prompter.text({
+            message: "Enter Mattermost bot token",
+            validate: (value) => (value?.trim() ? undefined : "Required"),
+          }),
+        ).trim();
+        baseUrl = String(
+          await prompter.text({
+            message: "Enter Mattermost base URL",
+            validate: (value) => (value?.trim() ? undefined : "Required"),
+          }),
+        ).trim();
+      }
+    } else if (accountConfigured) {
+      const keep = await prompter.confirm({
+        message: "Mattermost credentials already configured. Keep them?",
+        initialValue: true,
+      });
+      if (!keep) {
+        botToken = String(
+          await prompter.text({
+            message: "Enter Mattermost bot token",
+            validate: (value) => (value?.trim() ? undefined : "Required"),
+          }),
+        ).trim();
+        baseUrl = String(
+          await prompter.text({
+            message: "Enter Mattermost base URL",
+            validate: (value) => (value?.trim() ? undefined : "Required"),
+          }),
+        ).trim();
+      }
+    } else {
+      botToken = String(
+        await prompter.text({
+          message: "Enter Mattermost bot token",
+          validate: (value) => (value?.trim() ? undefined : "Required"),
+        }),
+      ).trim();
+      baseUrl = String(
+        await prompter.text({
+          message: "Enter Mattermost base URL",
+          validate: (value) => (value?.trim() ? undefined : "Required"),
+        }),
+      ).trim();
+    }
+
+    if (botToken || baseUrl) {
+      if (accountId === DEFAULT_ACCOUNT_ID) {
+        next = {
+          ...next,
+          channels: {
+            ...next.channels,
+            mattermost: {
+              ...next.channels?.mattermost,
+              enabled: true,
+              ...(botToken ? { botToken } : {}),
+              ...(baseUrl ? { baseUrl } : {}),
+            },
+          },
+        };
+      } else {
+        next = {
+          ...next,
+          channels: {
+            ...next.channels,
+            mattermost: {
+              ...next.channels?.mattermost,
+              enabled: true,
+              accounts: {
+                ...next.channels?.mattermost?.accounts,
+                [accountId]: {
+                  ...next.channels?.mattermost?.accounts?.[accountId],
+                  enabled: next.channels?.mattermost?.accounts?.[accountId]?.enabled ?? true,
+                  ...(botToken ? { botToken } : {}),
+                  ...(baseUrl ? { baseUrl } : {}),
+                },
+              },
+            },
+          },
+        };
+      }
+    }
+
+    return { cfg: next, accountId };
+  },
+  disable: (cfg: ClawdbotConfig) => ({
+    ...cfg,
+    channels: {
+      ...cfg.channels,
+      mattermost: { ...cfg.channels?.mattermost, enabled: false },
+    },
+  }),
+};
diff --git a/src/channels/registry.ts b/src/channels/registry.ts
index 52e7a5f01..25fb13502 100644
--- a/src/channels/registry.ts
+++ b/src/channels/registry.ts
@@ -9,6 +9,7 @@ export const CHAT_CHANNEL_ORDER = [
   "whatsapp",
   "discord",
   "slack",
+  "mattermost",
   "signal",
   "imessage",
 ] as const;
@@ -67,6 +68,16 @@ const CHAT_CHANNEL_META: Record<ChatChannelId, ChannelMeta> = {
     blurb: "supported (Socket Mode).",
     systemImage: "number",
   },
+  mattermost: {
+    id: "mattermost",
+    label: "Mattermost",
+    selectionLabel: "Mattermost (Bot Token)",
+    detailLabel: "Mattermost Bot",
+    docsPath: "/channels/mattermost",
+    docsLabel: "mattermost",
+    blurb: "self-hosted Slack-style chat (bot token + URL).",
+    systemImage: "bubble.left.and.bubble.right",
+  },
   signal: {
     id: "signal",
     label: "Signal",
diff --git a/src/commands/channels/resolve.ts b/src/commands/channels/resolve.ts
index 7394fa30f..820b53bf0 100644
--- a/src/commands/channels/resolve.ts
+++ b/src/commands/channels/resolve.ts
@@ -35,7 +35,7 @@ function detectAutoKind(input: string): ChannelResolveKind {
   if (!trimmed) return "group";
   if (trimmed.startsWith("@")) return "user";
   if (/^<@!?/.test(trimmed)) return "user";
-  if (/^(user|discord|slack|matrix|msteams|teams|zalo|zalouser):/i.test(trimmed)) {
+  if (/^(user|discord|slack|mattermost|matrix|msteams|teams|zalo|zalouser):/i.test(trimmed)) {
     return "user";
   }
   return "group";
diff --git a/src/config/io.ts b/src/config/io.ts
index d275d3185..34b534285 100644
--- a/src/config/io.ts
+++ b/src/config/io.ts
@@ -52,6 +52,8 @@ const SHELL_ENV_EXPECTED_KEYS = [
   "DISCORD_BOT_TOKEN",
   "SLACK_BOT_TOKEN",
   "SLACK_APP_TOKEN",
+  "MATTERMOST_BOT_TOKEN",
+  "MATTERMOST_URL",
   "CLAWDBOT_GATEWAY_TOKEN",
   "CLAWDBOT_GATEWAY_PASSWORD",
 ];
diff --git a/src/config/legacy.migrations.part-1.ts b/src/config/legacy.migrations.part-1.ts
index d1d0a57e7..8658b0ece 100644
--- a/src/config/legacy.migrations.part-1.ts
+++ b/src/config/legacy.migrations.part-1.ts
@@ -124,6 +124,7 @@ export const LEGACY_CONFIG_MIGRATIONS_PART_1: LegacyConfigMigration[] = [
         "telegram",
         "discord",
         "slack",
+        "mattermost",
         "signal",
         "imessage",
         "msteams",
diff --git a/src/config/legacy.rules.ts b/src/config/legacy.rules.ts
index 1ec76bc79..388083ae7 100644
--- a/src/config/legacy.rules.ts
+++ b/src/config/legacy.rules.ts
@@ -17,6 +17,10 @@ export const LEGACY_CONFIG_RULES: LegacyConfigRule[] = [
     path: ["slack"],
     message: "slack config moved to channels.slack (auto-migrated on load).",
   },
+  {
+    path: ["mattermost"],
+    message: "mattermost config moved to channels.mattermost (auto-migrated on load).",
+  },
   {
     path: ["signal"],
     message: "signal config moved to channels.signal (auto-migrated on load).",
diff --git a/src/config/schema.ts b/src/config/schema.ts
index 1ba527439..21f461ec0 100644
--- a/src/config/schema.ts
+++ b/src/config/schema.ts
@@ -272,6 +272,7 @@ const FIELD_LABELS: Record<string, string> = {
   "channels.telegram.customCommands": "Telegram Custom Commands",
   "channels.discord": "Discord",
   "channels.slack": "Slack",
+  "channels.mattermost": "Mattermost",
   "channels.signal": "Signal",
   "channels.imessage": "iMessage",
   "channels.bluebubbles": "BlueBubbles",
@@ -309,6 +310,11 @@ const FIELD_LABELS: Record<string, string> = {
   "channels.slack.userTokenReadOnly": "Slack User Token Read Only",
   "channels.slack.thread.historyScope": "Slack Thread History Scope",
   "channels.slack.thread.inheritParent": "Slack Thread Parent Inheritance",
+  "channels.mattermost.botToken": "Mattermost Bot Token",
+  "channels.mattermost.baseUrl": "Mattermost Base URL",
+  "channels.mattermost.chatmode": "Mattermost Chat Mode",
+  "channels.mattermost.oncharPrefixes": "Mattermost Onchar Prefixes",
+  "channels.mattermost.requireMention": "Mattermost Require Mention",
   "channels.signal.account": "Signal Account",
   "channels.imessage.cliPath": "iMessage CLI Path",
   "plugins.enabled": "Enable Plugins",
@@ -415,6 +421,15 @@ const FIELD_HELP: Record<string, string> = {
     'Scope for Slack thread history context ("thread" isolates per thread; "channel" reuses channel history).',
   "channels.slack.thread.inheritParent":
     "If true, Slack thread sessions inherit the parent channel transcript (default: false).",
+  "channels.mattermost.botToken":
+    "Bot token from Mattermost System Console -> Integrations -> Bot Accounts.",
+  "channels.mattermost.baseUrl":
+    "Base URL for your Mattermost server (e.g., https://chat.example.com).",
+  "channels.mattermost.chatmode":
+    'Reply to channel messages on mention ("oncall"), on trigger chars (">" or "!") ("onchar"), or on every message ("onmessage").',
+  "channels.mattermost.oncharPrefixes": 'Trigger prefixes for onchar mode (default: [">", "!"]).',
+  "channels.mattermost.requireMention":
+    "Require @mention in channels before responding (default: true).",
   "auth.profiles": "Named auth profiles (provider + mode + optional email).",
   "auth.order": "Ordered auth profile IDs per provider (used for automatic failover).",
   "auth.cooldowns.billingBackoffHours":
@@ -532,6 +547,8 @@ const FIELD_HELP: Record<string, string> = {
     "Allow Telegram to write config in response to channel events/commands (default: true).",
   "channels.slack.configWrites":
     "Allow Slack to write config in response to channel events/commands (default: true).",
+  "channels.mattermost.configWrites":
+    "Allow Mattermost to write config in response to channel events/commands (default: true).",
   "channels.discord.configWrites":
     "Allow Discord to write config in response to channel events/commands (default: true).",
   "channels.whatsapp.configWrites":
@@ -606,6 +623,7 @@ const FIELD_PLACEHOLDERS: Record<string, string> = {
   "gateway.remote.tlsFingerprint": "sha256:ab12cd34…",
   "gateway.remote.sshTarget": "user@host",
   "gateway.controlUi.basePath": "/clawdbot",
+  "channels.mattermost.baseUrl": "https://chat.example.com",
 };
 
 const SENSITIVE_PATTERNS = [/token/i, /password/i, /secret/i, /api.?key/i];
diff --git a/src/config/types.agent-defaults.ts b/src/config/types.agent-defaults.ts
index 85eff97f2..10066bd75 100644
--- a/src/config/types.agent-defaults.ts
+++ b/src/config/types.agent-defaults.ts
@@ -162,13 +162,14 @@ export type AgentDefaultsConfig = {
     every?: string;
     /** Heartbeat model override (provider/model). */
     model?: string;
-    /** Delivery target (last|whatsapp|telegram|discord|slack|msteams|signal|imessage|none). */
+    /** Delivery target (last|whatsapp|telegram|discord|slack|mattermost|msteams|signal|imessage|none). */
     target?:
       | "last"
       | "whatsapp"
       | "telegram"
       | "discord"
       | "slack"
+      | "mattermost"
       | "msteams"
       | "signal"
       | "imessage"
diff --git a/src/config/types.channels.ts b/src/config/types.channels.ts
index ac98e20de..19ac014dd 100644
--- a/src/config/types.channels.ts
+++ b/src/config/types.channels.ts
@@ -1,5 +1,6 @@
 import type { DiscordConfig } from "./types.discord.js";
 import type { IMessageConfig } from "./types.imessage.js";
+import type { MattermostConfig } from "./types.mattermost.js";
 import type { MSTeamsConfig } from "./types.msteams.js";
 import type { SignalConfig } from "./types.signal.js";
 import type { SlackConfig } from "./types.slack.js";
@@ -17,6 +18,7 @@ export type ChannelsConfig = {
   telegram?: TelegramConfig;
   discord?: DiscordConfig;
   slack?: SlackConfig;
+  mattermost?: MattermostConfig;
   signal?: SignalConfig;
   imessage?: IMessageConfig;
   msteams?: MSTeamsConfig;
diff --git a/src/config/types.hooks.ts b/src/config/types.hooks.ts
index 03e9250b2..2a5bf0f2f 100644
--- a/src/config/types.hooks.ts
+++ b/src/config/types.hooks.ts
@@ -24,6 +24,7 @@ export type HookMappingConfig = {
     | "telegram"
     | "discord"
     | "slack"
+    | "mattermost"
     | "signal"
     | "imessage"
     | "msteams";
diff --git a/src/config/types.mattermost.ts b/src/config/types.mattermost.ts
new file mode 100644
index 000000000..b87bdfabe
--- /dev/null
+++ b/src/config/types.mattermost.ts
@@ -0,0 +1,40 @@
+import type { BlockStreamingCoalesceConfig } from "./types.base.js";
+
+export type MattermostChatMode = "oncall" | "onmessage" | "onchar";
+
+export type MattermostAccountConfig = {
+  /** Optional display name for this account (used in CLI/UI lists). */
+  name?: string;
+  /** Optional provider capability tags used for agent/runtime guidance. */
+  capabilities?: string[];
+  /** Allow channel-initiated config writes (default: true). */
+  configWrites?: boolean;
+  /** If false, do not start this Mattermost account. Default: true. */
+  enabled?: boolean;
+  /** Bot token for Mattermost. */
+  botToken?: string;
+  /** Base URL for the Mattermost server (e.g., https://chat.example.com). */
+  baseUrl?: string;
+  /**
+   * Controls when channel messages trigger replies.
+   * - "oncall": only respond when mentioned
+   * - "onmessage": respond to every channel message
+   * - "onchar": respond when a trigger character prefixes the message
+   */
+  chatmode?: MattermostChatMode;
+  /** Prefix characters that trigger onchar mode (default: [">", "!"]). */
+  oncharPrefixes?: string[];
+  /** Require @mention to respond in channels. Default: true. */
+  requireMention?: boolean;
+  /** Outbound text chunk size (chars). Default: 4000. */
+  textChunkLimit?: number;
+  /** Disable block streaming for this account. */
+  blockStreaming?: boolean;
+  /** Merge streamed block replies before sending. */
+  blockStreamingCoalesce?: BlockStreamingCoalesceConfig;
+};
+
+export type MattermostConfig = {
+  /** Optional per-account Mattermost configuration (multi-account). */
+  accounts?: Record<string, MattermostAccountConfig>;
+} & MattermostAccountConfig;
diff --git a/src/config/types.messages.ts b/src/config/types.messages.ts
index 691ca617a..fc4146bc7 100644
--- a/src/config/types.messages.ts
+++ b/src/config/types.messages.ts
@@ -22,6 +22,7 @@ export type InboundDebounceByProvider = {
   telegram?: number;
   discord?: number;
   slack?: number;
+  mattermost?: number;
   signal?: number;
   imessage?: number;
   msteams?: number;
diff --git a/src/config/types.queue.ts b/src/config/types.queue.ts
index 0afeb5232..6289e7c56 100644
--- a/src/config/types.queue.ts
+++ b/src/config/types.queue.ts
@@ -13,6 +13,7 @@ export type QueueModeByProvider = {
   telegram?: QueueMode;
   discord?: QueueMode;
   slack?: QueueMode;
+  mattermost?: QueueMode;
   signal?: QueueMode;
   imessage?: QueueMode;
   msteams?: QueueMode;
diff --git a/src/config/types.ts b/src/config/types.ts
index 368618262..46e79eaca 100644
--- a/src/config/types.ts
+++ b/src/config/types.ts
@@ -14,6 +14,7 @@ export * from "./types.hooks.js";
 export * from "./types.imessage.js";
 export * from "./types.messages.js";
 export * from "./types.models.js";
+export * from "./types.mattermost.js";
 export * from "./types.msteams.js";
 export * from "./types.plugins.js";
 export * from "./types.queue.js";
diff --git a/src/config/zod-schema.agent-runtime.ts b/src/config/zod-schema.agent-runtime.ts
index 40dea6eb4..774645a14 100644
--- a/src/config/zod-schema.agent-runtime.ts
+++ b/src/config/zod-schema.agent-runtime.ts
@@ -20,6 +20,7 @@ export const HeartbeatSchema = z
         z.literal("telegram"),
         z.literal("discord"),
         z.literal("slack"),
+        z.literal("mattermost"),
         z.literal("msteams"),
         z.literal("signal"),
         z.literal("imessage"),
diff --git a/src/config/zod-schema.core.ts b/src/config/zod-schema.core.ts
index 6e7b34b0d..1d6612aae 100644
--- a/src/config/zod-schema.core.ts
+++ b/src/config/zod-schema.core.ts
@@ -208,6 +208,7 @@ export const QueueModeBySurfaceSchema = z
     telegram: QueueModeSchema.optional(),
     discord: QueueModeSchema.optional(),
     slack: QueueModeSchema.optional(),
+    mattermost: QueueModeSchema.optional(),
     signal: QueueModeSchema.optional(),
     imessage: QueueModeSchema.optional(),
     msteams: QueueModeSchema.optional(),
@@ -222,6 +223,7 @@ export const DebounceMsBySurfaceSchema = z
     telegram: z.number().int().nonnegative().optional(),
     discord: z.number().int().nonnegative().optional(),
     slack: z.number().int().nonnegative().optional(),
+    mattermost: z.number().int().nonnegative().optional(),
     signal: z.number().int().nonnegative().optional(),
     imessage: z.number().int().nonnegative().optional(),
     msteams: z.number().int().nonnegative().optional(),
diff --git a/src/config/zod-schema.hooks.ts b/src/config/zod-schema.hooks.ts
index 140e861dd..9153aa130 100644
--- a/src/config/zod-schema.hooks.ts
+++ b/src/config/zod-schema.hooks.ts
@@ -23,6 +23,7 @@ export const HookMappingSchema = z
         z.literal("telegram"),
         z.literal("discord"),
         z.literal("slack"),
+        z.literal("mattermost"),
         z.literal("signal"),
         z.literal("imessage"),
         z.literal("msteams"),
diff --git a/src/config/zod-schema.providers-core.ts b/src/config/zod-schema.providers-core.ts
index 906ef5433..200ff18c8 100644
--- a/src/config/zod-schema.providers-core.ts
+++ b/src/config/zod-schema.providers-core.ts
@@ -367,6 +367,27 @@ export const SlackConfigSchema = SlackAccountSchema.extend({
   }
 });
 
+export const MattermostAccountSchema = z
+  .object({
+    name: z.string().optional(),
+    capabilities: z.array(z.string()).optional(),
+    enabled: z.boolean().optional(),
+    configWrites: z.boolean().optional(),
+    botToken: z.string().optional(),
+    baseUrl: z.string().optional(),
+    chatmode: z.enum(["oncall", "onmessage", "onchar"]).optional(),
+    oncharPrefixes: z.array(z.string()).optional(),
+    requireMention: z.boolean().optional(),
+    textChunkLimit: z.number().int().positive().optional(),
+    blockStreaming: z.boolean().optional(),
+    blockStreamingCoalesce: BlockStreamingCoalesceSchema.optional(),
+  })
+  .strict();
+
+export const MattermostConfigSchema = MattermostAccountSchema.extend({
+  accounts: z.record(z.string(), MattermostAccountSchema.optional()).optional(),
+});
+
 export const SignalAccountSchemaBase = z
   .object({
     name: z.string().optional(),
diff --git a/src/config/zod-schema.providers.ts b/src/config/zod-schema.providers.ts
index a58119702..aa5eb7737 100644
--- a/src/config/zod-schema.providers.ts
+++ b/src/config/zod-schema.providers.ts
@@ -4,6 +4,7 @@ import {
   BlueBubblesConfigSchema,
   DiscordConfigSchema,
   IMessageConfigSchema,
+  MattermostConfigSchema,
   MSTeamsConfigSchema,
   SignalConfigSchema,
   SlackConfigSchema,
@@ -27,6 +28,7 @@ export const ChannelsSchema = z
     telegram: TelegramConfigSchema.optional(),
     discord: DiscordConfigSchema.optional(),
     slack: SlackConfigSchema.optional(),
+    mattermost: MattermostConfigSchema.optional(),
     signal: SignalConfigSchema.optional(),
     imessage: IMessageConfigSchema.optional(),
     bluebubbles: BlueBubblesConfigSchema.optional(),
diff --git a/src/infra/outbound/deliver.ts b/src/infra/outbound/deliver.ts
index 21fffe807..74caa18c6 100644
--- a/src/infra/outbound/deliver.ts
+++ b/src/infra/outbound/deliver.ts
@@ -6,6 +6,7 @@ import type { ChannelOutboundAdapter } from "../../channels/plugins/types.js";
 import type { ClawdbotConfig } from "../../config/config.js";
 import type { sendMessageDiscord } from "../../discord/send.js";
 import type { sendMessageIMessage } from "../../imessage/send.js";
+import type { sendMessageMattermost } from "../../mattermost/send.js";
 import { markdownToSignalTextChunks, type SignalTextStyleRange } from "../../signal/format.js";
 import { sendMessageSignal } from "../../signal/send.js";
 import type { sendMessageSlack } from "../../slack/send.js";
@@ -33,6 +34,7 @@ export type OutboundSendDeps = {
   sendTelegram?: typeof sendMessageTelegram;
   sendDiscord?: typeof sendMessageDiscord;
   sendSlack?: typeof sendMessageSlack;
+  sendMattermost?: typeof sendMessageMattermost;
   sendSignal?: typeof sendMessageSignal;
   sendIMessage?: typeof sendMessageIMessage;
   sendMatrix?: SendMatrixMessage;
diff --git a/src/mattermost/accounts.ts b/src/mattermost/accounts.ts
new file mode 100644
index 000000000..08ffa2f94
--- /dev/null
+++ b/src/mattermost/accounts.ts
@@ -0,0 +1,114 @@
+import type { ClawdbotConfig } from "../config/config.js";
+import type { MattermostAccountConfig, MattermostChatMode } from "../config/types.js";
+import { DEFAULT_ACCOUNT_ID, normalizeAccountId } from "../routing/session-key.js";
+import { normalizeMattermostBaseUrl } from "./client.js";
+
+export type MattermostTokenSource = "env" | "config" | "none";
+export type MattermostBaseUrlSource = "env" | "config" | "none";
+
+export type ResolvedMattermostAccount = {
+  accountId: string;
+  enabled: boolean;
+  name?: string;
+  botToken?: string;
+  baseUrl?: string;
+  botTokenSource: MattermostTokenSource;
+  baseUrlSource: MattermostBaseUrlSource;
+  config: MattermostAccountConfig;
+  chatmode?: MattermostChatMode;
+  oncharPrefixes?: string[];
+  requireMention?: boolean;
+  textChunkLimit?: number;
+  blockStreaming?: boolean;
+  blockStreamingCoalesce?: MattermostAccountConfig["blockStreamingCoalesce"];
+};
+
+function listConfiguredAccountIds(cfg: ClawdbotConfig): string[] {
+  const accounts = cfg.channels?.mattermost?.accounts;
+  if (!accounts || typeof accounts !== "object") return [];
+  return Object.keys(accounts).filter(Boolean);
+}
+
+export function listMattermostAccountIds(cfg: ClawdbotConfig): string[] {
+  const ids = listConfiguredAccountIds(cfg);
+  if (ids.length === 0) return [DEFAULT_ACCOUNT_ID];
+  return ids.sort((a, b) => a.localeCompare(b));
+}
+
+export function resolveDefaultMattermostAccountId(cfg: ClawdbotConfig): string {
+  const ids = listMattermostAccountIds(cfg);
+  if (ids.includes(DEFAULT_ACCOUNT_ID)) return DEFAULT_ACCOUNT_ID;
+  return ids[0] ?? DEFAULT_ACCOUNT_ID;
+}
+
+function resolveAccountConfig(
+  cfg: ClawdbotConfig,
+  accountId: string,
+): MattermostAccountConfig | undefined {
+  const accounts = cfg.channels?.mattermost?.accounts;
+  if (!accounts || typeof accounts !== "object") return undefined;
+  return accounts[accountId] as MattermostAccountConfig | undefined;
+}
+
+function mergeMattermostAccountConfig(
+  cfg: ClawdbotConfig,
+  accountId: string,
+): MattermostAccountConfig {
+  const { accounts: _ignored, ...base } = (cfg.channels?.mattermost ??
+    {}) as MattermostAccountConfig & { accounts?: unknown };
+  const account = resolveAccountConfig(cfg, accountId) ?? {};
+  return { ...base, ...account };
+}
+
+function resolveMattermostRequireMention(config: MattermostAccountConfig): boolean | undefined {
+  if (config.chatmode === "oncall") return true;
+  if (config.chatmode === "onmessage") return false;
+  if (config.chatmode === "onchar") return true;
+  return config.requireMention;
+}
+
+export function resolveMattermostAccount(params: {
+  cfg: ClawdbotConfig;
+  accountId?: string | null;
+}): ResolvedMattermostAccount {
+  const accountId = normalizeAccountId(params.accountId);
+  const baseEnabled = params.cfg.channels?.mattermost?.enabled !== false;
+  const merged = mergeMattermostAccountConfig(params.cfg, accountId);
+  const accountEnabled = merged.enabled !== false;
+  const enabled = baseEnabled && accountEnabled;
+
+  const allowEnv = accountId === DEFAULT_ACCOUNT_ID;
+  const envToken = allowEnv ? process.env.MATTERMOST_BOT_TOKEN?.trim() : undefined;
+  const envUrl = allowEnv ? process.env.MATTERMOST_URL?.trim() : undefined;
+  const configToken = merged.botToken?.trim();
+  const configUrl = merged.baseUrl?.trim();
+  const botToken = configToken || envToken;
+  const baseUrl = normalizeMattermostBaseUrl(configUrl || envUrl);
+  const requireMention = resolveMattermostRequireMention(merged);
+
+  const botTokenSource: MattermostTokenSource = configToken ? "config" : envToken ? "env" : "none";
+  const baseUrlSource: MattermostBaseUrlSource = configUrl ? "config" : envUrl ? "env" : "none";
+
+  return {
+    accountId,
+    enabled,
+    name: merged.name?.trim() || undefined,
+    botToken,
+    baseUrl,
+    botTokenSource,
+    baseUrlSource,
+    config: merged,
+    chatmode: merged.chatmode,
+    oncharPrefixes: merged.oncharPrefixes,
+    requireMention,
+    textChunkLimit: merged.textChunkLimit,
+    blockStreaming: merged.blockStreaming,
+    blockStreamingCoalesce: merged.blockStreamingCoalesce,
+  };
+}
+
+export function listEnabledMattermostAccounts(cfg: ClawdbotConfig): ResolvedMattermostAccount[] {
+  return listMattermostAccountIds(cfg)
+    .map((accountId) => resolveMattermostAccount({ cfg, accountId }))
+    .filter((account) => account.enabled);
+}
diff --git a/src/mattermost/client.ts b/src/mattermost/client.ts
new file mode 100644
index 000000000..6b63f830f
--- /dev/null
+++ b/src/mattermost/client.ts
@@ -0,0 +1,208 @@
+export type MattermostClient = {
+  baseUrl: string;
+  apiBaseUrl: string;
+  token: string;
+  request: <T>(path: string, init?: RequestInit) => Promise<T>;
+};
+
+export type MattermostUser = {
+  id: string;
+  username?: string | null;
+  nickname?: string | null;
+  first_name?: string | null;
+  last_name?: string | null;
+};
+
+export type MattermostChannel = {
+  id: string;
+  name?: string | null;
+  display_name?: string | null;
+  type?: string | null;
+  team_id?: string | null;
+};
+
+export type MattermostPost = {
+  id: string;
+  user_id?: string | null;
+  channel_id?: string | null;
+  message?: string | null;
+  file_ids?: string[] | null;
+  type?: string | null;
+  root_id?: string | null;
+  create_at?: number | null;
+  props?: Record<string, unknown> | null;
+};
+
+export type MattermostFileInfo = {
+  id: string;
+  name?: string | null;
+  mime_type?: string | null;
+  size?: number | null;
+};
+
+export function normalizeMattermostBaseUrl(raw?: string | null): string | undefined {
+  const trimmed = raw?.trim();
+  if (!trimmed) return undefined;
+  const withoutTrailing = trimmed.replace(/\/+$/, "");
+  return withoutTrailing.replace(/\/api\/v4$/i, "");
+}
+
+function buildMattermostApiUrl(baseUrl: string, path: string): string {
+  const normalized = normalizeMattermostBaseUrl(baseUrl);
+  if (!normalized) throw new Error("Mattermost baseUrl is required");
+  const suffix = path.startsWith("/") ? path : `/${path}`;
+  return `${normalized}/api/v4${suffix}`;
+}
+
+async function readMattermostError(res: Response): Promise<string> {
+  const contentType = res.headers.get("content-type") ?? "";
+  if (contentType.includes("application/json")) {
+    const data = (await res.json()) as { message?: string } | undefined;
+    if (data?.message) return data.message;
+    return JSON.stringify(data);
+  }
+  return await res.text();
+}
+
+export function createMattermostClient(params: {
+  baseUrl: string;
+  botToken: string;
+  fetchImpl?: typeof fetch;
+}): MattermostClient {
+  const baseUrl = normalizeMattermostBaseUrl(params.baseUrl);
+  if (!baseUrl) throw new Error("Mattermost baseUrl is required");
+  const apiBaseUrl = `${baseUrl}/api/v4`;
+  const token = params.botToken.trim();
+  const fetchImpl = params.fetchImpl ?? fetch;
+
+  const request = async <T>(path: string, init?: RequestInit): Promise<T> => {
+    const url = buildMattermostApiUrl(baseUrl, path);
+    const headers = new Headers(init?.headers);
+    headers.set("Authorization", `Bearer ${token}`);
+    if (typeof init?.body === "string" && !headers.has("Content-Type")) {
+      headers.set("Content-Type", "application/json");
+    }
+    const res = await fetchImpl(url, { ...init, headers });
+    if (!res.ok) {
+      const detail = await readMattermostError(res);
+      throw new Error(
+        `Mattermost API ${res.status} ${res.statusText}: ${detail || "unknown error"}`,
+      );
+    }
+    return (await res.json()) as T;
+  };
+
+  return { baseUrl, apiBaseUrl, token, request };
+}
+
+export async function fetchMattermostMe(client: MattermostClient): Promise<MattermostUser> {
+  return await client.request<MattermostUser>("/users/me");
+}
+
+export async function fetchMattermostUser(
+  client: MattermostClient,
+  userId: string,
+): Promise<MattermostUser> {
+  return await client.request<MattermostUser>(`/users/${userId}`);
+}
+
+export async function fetchMattermostUserByUsername(
+  client: MattermostClient,
+  username: string,
+): Promise<MattermostUser> {
+  return await client.request<MattermostUser>(`/users/username/${encodeURIComponent(username)}`);
+}
+
+export async function fetchMattermostChannel(
+  client: MattermostClient,
+  channelId: string,
+): Promise<MattermostChannel> {
+  return await client.request<MattermostChannel>(`/channels/${channelId}`);
+}
+
+export async function sendMattermostTyping(
+  client: MattermostClient,
+  params: { channelId: string; parentId?: string },
+): Promise<void> {
+  const payload: Record<string, string> = {
+    channel_id: params.channelId,
+  };
+  const parentId = params.parentId?.trim();
+  if (parentId) payload.parent_id = parentId;
+  await client.request<Record<string, unknown>>("/users/me/typing", {
+    method: "POST",
+    body: JSON.stringify(payload),
+  });
+}
+
+export async function createMattermostDirectChannel(
+  client: MattermostClient,
+  userIds: string[],
+): Promise<MattermostChannel> {
+  return await client.request<MattermostChannel>("/channels/direct", {
+    method: "POST",
+    body: JSON.stringify(userIds),
+  });
+}
+
+export async function createMattermostPost(
+  client: MattermostClient,
+  params: {
+    channelId: string;
+    message: string;
+    rootId?: string;
+    fileIds?: string[];
+  },
+): Promise<MattermostPost> {
+  const payload: Record<string, string> = {
+    channel_id: params.channelId,
+    message: params.message,
+  };
+  if (params.rootId) payload.root_id = params.rootId;
+  if (params.fileIds?.length) {
+    (payload as Record<string, unknown>).file_ids = params.fileIds;
+  }
+  return await client.request<MattermostPost>("/posts", {
+    method: "POST",
+    body: JSON.stringify(payload),
+  });
+}
+
+export async function uploadMattermostFile(
+  client: MattermostClient,
+  params: {
+    channelId: string;
+    buffer: Buffer;
+    fileName: string;
+    contentType?: string;
+  },
+): Promise<MattermostFileInfo> {
+  const form = new FormData();
+  const fileName = params.fileName?.trim() || "upload";
+  const bytes = Uint8Array.from(params.buffer);
+  const blob = params.contentType
+    ? new Blob([bytes], { type: params.contentType })
+    : new Blob([bytes]);
+  form.append("files", blob, fileName);
+  form.append("channel_id", params.channelId);
+
+  const res = await fetch(`${client.apiBaseUrl}/files`, {
+    method: "POST",
+    headers: {
+      Authorization: `Bearer ${client.token}`,
+    },
+    body: form,
+  });
+
+  if (!res.ok) {
+    const detail = await readMattermostError(res);
+    throw new Error(`Mattermost API ${res.status} ${res.statusText}: ${detail || "unknown error"}`);
+  }
+
+  const data = (await res.json()) as { file_infos?: MattermostFileInfo[] };
+  const info = data.file_infos?.[0];
+  if (!info?.id) {
+    throw new Error("Mattermost file upload failed");
+  }
+  return info;
+}
diff --git a/src/mattermost/index.ts b/src/mattermost/index.ts
new file mode 100644
index 000000000..9d09fc402
--- /dev/null
+++ b/src/mattermost/index.ts
@@ -0,0 +1,9 @@
+export {
+  listEnabledMattermostAccounts,
+  listMattermostAccountIds,
+  resolveDefaultMattermostAccountId,
+  resolveMattermostAccount,
+} from "./accounts.js";
+export { monitorMattermostProvider } from "./monitor.js";
+export { probeMattermost } from "./probe.js";
+export { sendMessageMattermost } from "./send.js";
diff --git a/src/mattermost/monitor.ts b/src/mattermost/monitor.ts
new file mode 100644
index 000000000..fb8bd00db
--- /dev/null
+++ b/src/mattermost/monitor.ts
@@ -0,0 +1,774 @@
+import WebSocket from "ws";
+
+import {
+  resolveEffectiveMessagesConfig,
+  resolveHumanDelayConfig,
+  resolveIdentityName,
+} from "../agents/identity.js";
+import { chunkMarkdownText, resolveTextChunkLimit } from "../auto-reply/chunk.js";
+import { hasControlCommand } from "../auto-reply/command-detection.js";
+import { shouldHandleTextCommands } from "../auto-reply/commands-registry.js";
+import { formatInboundEnvelope, formatInboundFromLabel } from "../auto-reply/envelope.js";
+import {
+  createInboundDebouncer,
+  resolveInboundDebounceMs,
+} from "../auto-reply/inbound-debounce.js";
+import { dispatchReplyFromConfig } from "../auto-reply/reply/dispatch-from-config.js";
+import { finalizeInboundContext } from "../auto-reply/reply/inbound-context.js";
+import {
+  buildPendingHistoryContextFromMap,
+  clearHistoryEntries,
+  DEFAULT_GROUP_HISTORY_LIMIT,
+  recordPendingHistoryEntry,
+  type HistoryEntry,
+} from "../auto-reply/reply/history.js";
+import { createReplyDispatcherWithTyping } from "../auto-reply/reply/reply-dispatcher.js";
+import {
+  extractShortModelName,
+  type ResponsePrefixContext,
+} from "../auto-reply/reply/response-prefix-template.js";
+import { buildMentionRegexes, matchesMentionPatterns } from "../auto-reply/reply/mentions.js";
+import type { ReplyPayload } from "../auto-reply/types.js";
+import type { ClawdbotConfig } from "../config/config.js";
+import { loadConfig } from "../config/config.js";
+import { resolveStorePath, updateLastRoute } from "../config/sessions.js";
+import { danger, logVerbose, shouldLogVerbose } from "../globals.js";
+import { createDedupeCache } from "../infra/dedupe.js";
+import { rawDataToString } from "../infra/ws.js";
+import { recordChannelActivity } from "../infra/channel-activity.js";
+import { enqueueSystemEvent } from "../infra/system-events.js";
+import { getChildLogger } from "../logging.js";
+import { mediaKindFromMime, type MediaKind } from "../media/constants.js";
+import { fetchRemoteMedia, type FetchLike } from "../media/fetch.js";
+import { saveMediaBuffer } from "../media/store.js";
+import { resolveAgentRoute } from "../routing/resolve-route.js";
+import { resolveThreadSessionKeys } from "../routing/session-key.js";
+import type { RuntimeEnv } from "../runtime.js";
+import type { ChannelAccountSnapshot } from "../channels/plugins/types.js";
+import { resolveChannelMediaMaxBytes } from "../channels/plugins/media-limits.js";
+import { resolveCommandAuthorizedFromAuthorizers } from "../channels/command-gating.js";
+import { resolveMattermostAccount } from "./accounts.js";
+import {
+  createMattermostClient,
+  fetchMattermostChannel,
+  fetchMattermostMe,
+  fetchMattermostUser,
+  normalizeMattermostBaseUrl,
+  sendMattermostTyping,
+  type MattermostChannel,
+  type MattermostPost,
+  type MattermostUser,
+} from "./client.js";
+import { sendMessageMattermost } from "./send.js";
+
+export type MonitorMattermostOpts = {
+  botToken?: string;
+  baseUrl?: string;
+  accountId?: string;
+  config?: ClawdbotConfig;
+  runtime?: RuntimeEnv;
+  abortSignal?: AbortSignal;
+  statusSink?: (patch: Partial<ChannelAccountSnapshot>) => void;
+};
+
+type MattermostEventPayload = {
+  event?: string;
+  data?: {
+    post?: string;
+    channel_id?: string;
+    channel_name?: string;
+    channel_display_name?: string;
+    channel_type?: string;
+    sender_name?: string;
+    team_id?: string;
+  };
+  broadcast?: {
+    channel_id?: string;
+    team_id?: string;
+    user_id?: string;
+  };
+};
+
+const RECENT_MATTERMOST_MESSAGE_TTL_MS = 5 * 60_000;
+const RECENT_MATTERMOST_MESSAGE_MAX = 2000;
+const CHANNEL_CACHE_TTL_MS = 5 * 60_000;
+const USER_CACHE_TTL_MS = 10 * 60_000;
+const DEFAULT_ONCHAR_PREFIXES = [">", "!"];
+
+const recentInboundMessages = createDedupeCache({
+  ttlMs: RECENT_MATTERMOST_MESSAGE_TTL_MS,
+  maxSize: RECENT_MATTERMOST_MESSAGE_MAX,
+});
+
+function resolveRuntime(opts: MonitorMattermostOpts): RuntimeEnv {
+  return (
+    opts.runtime ?? {
+      log: console.log,
+      error: console.error,
+      exit: (code: number): never => {
+        throw new Error(`exit ${code}`);
+      },
+    }
+  );
+}
+
+function normalizeMention(text: string, mention: string | undefined): string {
+  if (!mention) return text.trim();
+  const escaped = mention.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+  const re = new RegExp(`@${escaped}\\b`, "gi");
+  return text.replace(re, " ").replace(/\s+/g, " ").trim();
+}
+
+function resolveOncharPrefixes(prefixes: string[] | undefined): string[] {
+  const cleaned = prefixes?.map((entry) => entry.trim()).filter(Boolean) ?? DEFAULT_ONCHAR_PREFIXES;
+  return cleaned.length > 0 ? cleaned : DEFAULT_ONCHAR_PREFIXES;
+}
+
+function stripOncharPrefix(
+  text: string,
+  prefixes: string[],
+): { triggered: boolean; stripped: string } {
+  const trimmed = text.trimStart();
+  for (const prefix of prefixes) {
+    if (!prefix) continue;
+    if (trimmed.startsWith(prefix)) {
+      return {
+        triggered: true,
+        stripped: trimmed.slice(prefix.length).trimStart(),
+      };
+    }
+  }
+  return { triggered: false, stripped: text };
+}
+
+function isSystemPost(post: MattermostPost): boolean {
+  const type = post.type?.trim();
+  return Boolean(type);
+}
+
+function channelKind(channelType?: string | null): "dm" | "group" | "channel" {
+  if (!channelType) return "channel";
+  const normalized = channelType.trim().toUpperCase();
+  if (normalized === "D") return "dm";
+  if (normalized === "G") return "group";
+  return "channel";
+}
+
+function channelChatType(kind: "dm" | "group" | "channel"): "direct" | "group" | "channel" {
+  if (kind === "dm") return "direct";
+  if (kind === "group") return "group";
+  return "channel";
+}
+
+type MattermostMediaInfo = {
+  path: string;
+  contentType?: string;
+  kind: MediaKind;
+};
+
+function buildMattermostAttachmentPlaceholder(mediaList: MattermostMediaInfo[]): string {
+  if (mediaList.length === 0) return "";
+  if (mediaList.length === 1) {
+    const kind = mediaList[0].kind === "unknown" ? "document" : mediaList[0].kind;
+    return `<media:${kind}>`;
+  }
+  const allImages = mediaList.every((media) => media.kind === "image");
+  const label = allImages ? "image" : "file";
+  const suffix = mediaList.length === 1 ? label : `${label}s`;
+  const tag = allImages ? "<media:image>" : "<media:document>";
+  return `${tag} (${mediaList.length} ${suffix})`;
+}
+
+function buildMattermostMediaPayload(mediaList: MattermostMediaInfo[]): {
+  MediaPath?: string;
+  MediaType?: string;
+  MediaUrl?: string;
+  MediaPaths?: string[];
+  MediaUrls?: string[];
+  MediaTypes?: string[];
+} {
+  const first = mediaList[0];
+  const mediaPaths = mediaList.map((media) => media.path);
+  const mediaTypes = mediaList.map((media) => media.contentType).filter(Boolean) as string[];
+  return {
+    MediaPath: first?.path,
+    MediaType: first?.contentType,
+    MediaUrl: first?.path,
+    MediaPaths: mediaPaths.length > 0 ? mediaPaths : undefined,
+    MediaUrls: mediaPaths.length > 0 ? mediaPaths : undefined,
+    MediaTypes: mediaTypes.length > 0 ? mediaTypes : undefined,
+  };
+}
+
+function buildMattermostWsUrl(baseUrl: string): string {
+  const normalized = normalizeMattermostBaseUrl(baseUrl);
+  if (!normalized) throw new Error("Mattermost baseUrl is required");
+  const wsBase = normalized.replace(/^http/i, "ws");
+  return `${wsBase}/api/v4/websocket`;
+}
+
+export async function monitorMattermostProvider(opts: MonitorMattermostOpts = {}): Promise<void> {
+  const runtime = resolveRuntime(opts);
+  const cfg = opts.config ?? loadConfig();
+  const account = resolveMattermostAccount({
+    cfg,
+    accountId: opts.accountId,
+  });
+  const botToken = opts.botToken?.trim() || account.botToken?.trim();
+  if (!botToken) {
+    throw new Error(
+      `Mattermost bot token missing for account "${account.accountId}" (set channels.mattermost.accounts.${account.accountId}.botToken or MATTERMOST_BOT_TOKEN for default).`,
+    );
+  }
+  const baseUrl = normalizeMattermostBaseUrl(opts.baseUrl ?? account.baseUrl);
+  if (!baseUrl) {
+    throw new Error(
+      `Mattermost baseUrl missing for account "${account.accountId}" (set channels.mattermost.accounts.${account.accountId}.baseUrl or MATTERMOST_URL for default).`,
+    );
+  }
+
+  const client = createMattermostClient({ baseUrl, botToken });
+  const botUser = await fetchMattermostMe(client);
+  const botUserId = botUser.id;
+  const botUsername = botUser.username?.trim() || undefined;
+  runtime.log?.(`mattermost connected as ${botUsername ? `@${botUsername}` : botUserId}`);
+
+  const channelCache = new Map<string, { value: MattermostChannel | null; expiresAt: number }>();
+  const userCache = new Map<string, { value: MattermostUser | null; expiresAt: number }>();
+  const logger = getChildLogger({ module: "mattermost" });
+  const mediaMaxBytes =
+    resolveChannelMediaMaxBytes({
+      cfg,
+      resolveChannelLimitMb: () => undefined,
+      accountId: account.accountId,
+    }) ?? 8 * 1024 * 1024;
+  const historyLimit = Math.max(
+    0,
+    cfg.messages?.groupChat?.historyLimit ?? DEFAULT_GROUP_HISTORY_LIMIT,
+  );
+  const channelHistories = new Map<string, HistoryEntry[]>();
+
+  const fetchWithAuth: FetchLike = (input, init) => {
+    const headers = new Headers(init?.headers);
+    headers.set("Authorization", `Bearer ${client.token}`);
+    return fetch(input, { ...init, headers });
+  };
+
+  const resolveMattermostMedia = async (
+    fileIds?: string[] | null,
+  ): Promise<MattermostMediaInfo[]> => {
+    const ids = (fileIds ?? []).map((id) => id?.trim()).filter(Boolean) as string[];
+    if (ids.length === 0) return [];
+    const out: MattermostMediaInfo[] = [];
+    for (const fileId of ids) {
+      try {
+        const fetched = await fetchRemoteMedia({
+          url: `${client.apiBaseUrl}/files/${fileId}`,
+          fetchImpl: fetchWithAuth,
+          filePathHint: fileId,
+          maxBytes: mediaMaxBytes,
+        });
+        const saved = await saveMediaBuffer(
+          fetched.buffer,
+          fetched.contentType ?? undefined,
+          "inbound",
+          mediaMaxBytes,
+        );
+        const contentType = saved.contentType ?? fetched.contentType ?? undefined;
+        out.push({
+          path: saved.path,
+          contentType,
+          kind: mediaKindFromMime(contentType),
+        });
+      } catch (err) {
+        logger.debug?.(`mattermost: failed to download file ${fileId}: ${String(err)}`);
+      }
+    }
+    return out;
+  };
+
+  const sendTypingIndicator = async (channelId: string, parentId?: string) => {
+    try {
+      await sendMattermostTyping(client, { channelId, parentId });
+    } catch (err) {
+      logger.debug?.(`mattermost typing cue failed for channel ${channelId}: ${String(err)}`);
+    }
+  };
+
+  const resolveChannelInfo = async (channelId: string): Promise<MattermostChannel | null> => {
+    const cached = channelCache.get(channelId);
+    if (cached && cached.expiresAt > Date.now()) return cached.value;
+    try {
+      const info = await fetchMattermostChannel(client, channelId);
+      channelCache.set(channelId, {
+        value: info,
+        expiresAt: Date.now() + CHANNEL_CACHE_TTL_MS,
+      });
+      return info;
+    } catch (err) {
+      logger.debug?.(`mattermost: channel lookup failed: ${String(err)}`);
+      channelCache.set(channelId, {
+        value: null,
+        expiresAt: Date.now() + CHANNEL_CACHE_TTL_MS,
+      });
+      return null;
+    }
+  };
+
+  const resolveUserInfo = async (userId: string): Promise<MattermostUser | null> => {
+    const cached = userCache.get(userId);
+    if (cached && cached.expiresAt > Date.now()) return cached.value;
+    try {
+      const info = await fetchMattermostUser(client, userId);
+      userCache.set(userId, {
+        value: info,
+        expiresAt: Date.now() + USER_CACHE_TTL_MS,
+      });
+      return info;
+    } catch (err) {
+      logger.debug?.(`mattermost: user lookup failed: ${String(err)}`);
+      userCache.set(userId, {
+        value: null,
+        expiresAt: Date.now() + USER_CACHE_TTL_MS,
+      });
+      return null;
+    }
+  };
+
+  const handlePost = async (
+    post: MattermostPost,
+    payload: MattermostEventPayload,
+    messageIds?: string[],
+  ) => {
+    const channelId = post.channel_id ?? payload.data?.channel_id ?? payload.broadcast?.channel_id;
+    if (!channelId) return;
+
+    const allMessageIds = messageIds?.length ? messageIds : post.id ? [post.id] : [];
+    if (allMessageIds.length === 0) return;
+    const dedupeEntries = allMessageIds.map((id) =>
+      recentInboundMessages.check(`${account.accountId}:${id}`),
+    );
+    if (dedupeEntries.length > 0 && dedupeEntries.every(Boolean)) return;
+
+    const senderId = post.user_id ?? payload.broadcast?.user_id;
+    if (!senderId) return;
+    if (senderId === botUserId) return;
+    if (isSystemPost(post)) return;
+
+    const channelInfo = await resolveChannelInfo(channelId);
+    const channelType = payload.data?.channel_type ?? channelInfo?.type ?? undefined;
+    const kind = channelKind(channelType);
+    const chatType = channelChatType(kind);
+
+    const teamId = payload.data?.team_id ?? channelInfo?.team_id ?? undefined;
+    const channelName = payload.data?.channel_name ?? channelInfo?.name ?? "";
+    const channelDisplay =
+      payload.data?.channel_display_name ?? channelInfo?.display_name ?? channelName;
+    const roomLabel = channelName ? `#${channelName}` : channelDisplay || `#${channelId}`;
+
+    const route = resolveAgentRoute({
+      cfg,
+      channel: "mattermost",
+      accountId: account.accountId,
+      teamId,
+      peer: {
+        kind,
+        id: kind === "dm" ? senderId : channelId,
+      },
+    });
+
+    const baseSessionKey = route.sessionKey;
+    const threadRootId = post.root_id?.trim() || undefined;
+    const threadKeys = resolveThreadSessionKeys({
+      baseSessionKey,
+      threadId: threadRootId,
+      parentSessionKey: threadRootId ? baseSessionKey : undefined,
+    });
+    const sessionKey = threadKeys.sessionKey;
+    const historyKey = kind === "dm" ? null : sessionKey;
+
+    const mentionRegexes = buildMentionRegexes(cfg, route.agentId);
+    const rawText = post.message?.trim() || "";
+    const wasMentioned =
+      kind !== "dm" &&
+      ((botUsername ? rawText.toLowerCase().includes(`@${botUsername.toLowerCase()}`) : false) ||
+        matchesMentionPatterns(rawText, mentionRegexes));
+    const pendingBody =
+      rawText ||
+      (post.file_ids?.length
+        ? `[Mattermost ${post.file_ids.length === 1 ? "file" : "files"}]`
+        : "");
+    const pendingSender = payload.data?.sender_name?.trim() || senderId;
+    const recordPendingHistory = () => {
+      if (!historyKey || historyLimit <= 0) return;
+      const trimmed = pendingBody.trim();
+      if (!trimmed) return;
+      recordPendingHistoryEntry({
+        historyMap: channelHistories,
+        historyKey,
+        limit: historyLimit,
+        entry: {
+          sender: pendingSender,
+          body: trimmed,
+          timestamp: typeof post.create_at === "number" ? post.create_at : undefined,
+          messageId: post.id ?? undefined,
+        },
+      });
+    };
+
+    const allowTextCommands = shouldHandleTextCommands({
+      cfg,
+      surface: "mattermost",
+    });
+    const isControlCommand = allowTextCommands && hasControlCommand(rawText, cfg);
+    const oncharEnabled = account.chatmode === "onchar" && kind !== "dm";
+    const oncharPrefixes = oncharEnabled ? resolveOncharPrefixes(account.oncharPrefixes) : [];
+    const oncharResult = oncharEnabled
+      ? stripOncharPrefix(rawText, oncharPrefixes)
+      : { triggered: false, stripped: rawText };
+    const oncharTriggered = oncharResult.triggered;
+
+    const shouldRequireMention = kind === "channel" && (account.requireMention ?? true);
+    const shouldBypassMention = isControlCommand && shouldRequireMention && !wasMentioned;
+    const effectiveWasMentioned = wasMentioned || shouldBypassMention || oncharTriggered;
+    const canDetectMention = Boolean(botUsername) || mentionRegexes.length > 0;
+
+    if (oncharEnabled && !oncharTriggered && !wasMentioned && !isControlCommand) {
+      recordPendingHistory();
+      return;
+    }
+
+    if (kind === "channel" && shouldRequireMention && canDetectMention) {
+      if (!effectiveWasMentioned) {
+        recordPendingHistory();
+        return;
+      }
+    }
+
+    const senderName =
+      payload.data?.sender_name?.trim() ||
+      (await resolveUserInfo(senderId))?.username?.trim() ||
+      senderId;
+    const mediaList = await resolveMattermostMedia(post.file_ids);
+    const mediaPlaceholder = buildMattermostAttachmentPlaceholder(mediaList);
+    const bodySource = oncharTriggered ? oncharResult.stripped : rawText;
+    const baseText = [bodySource, mediaPlaceholder].filter(Boolean).join("\n").trim();
+    const bodyText = normalizeMention(baseText, botUsername);
+    if (!bodyText) return;
+
+    recordChannelActivity({
+      channel: "mattermost",
+      accountId: account.accountId,
+      direction: "inbound",
+    });
+
+    const fromLabel = formatInboundFromLabel({
+      isGroup: kind !== "dm",
+      groupLabel: channelDisplay || roomLabel,
+      groupId: channelId,
+      groupFallback: roomLabel || "Channel",
+      directLabel: senderName,
+      directId: senderId,
+    });
+
+    const preview = bodyText.replace(/\s+/g, " ").slice(0, 160);
+    const inboundLabel =
+      kind === "dm"
+        ? `Mattermost DM from ${senderName}`
+        : `Mattermost message in ${roomLabel} from ${senderName}`;
+    enqueueSystemEvent(`${inboundLabel}: ${preview}`, {
+      sessionKey,
+      contextKey: `mattermost:message:${channelId}:${post.id ?? "unknown"}`,
+    });
+
+    const textWithId = `${bodyText}\n[mattermost message id: ${post.id ?? "unknown"} channel: ${channelId}]`;
+    const body = formatInboundEnvelope({
+      channel: "Mattermost",
+      from: fromLabel,
+      timestamp: typeof post.create_at === "number" ? post.create_at : undefined,
+      body: textWithId,
+      chatType,
+      sender: { name: senderName, id: senderId },
+    });
+    let combinedBody = body;
+    if (historyKey && historyLimit > 0) {
+      combinedBody = buildPendingHistoryContextFromMap({
+        historyMap: channelHistories,
+        historyKey,
+        limit: historyLimit,
+        currentMessage: combinedBody,
+        formatEntry: (entry) =>
+          formatInboundEnvelope({
+            channel: "Mattermost",
+            from: fromLabel,
+            timestamp: entry.timestamp,
+            body: `${entry.body}${
+              entry.messageId ? ` [id:${entry.messageId} channel:${channelId}]` : ""
+            }`,
+            chatType,
+            senderLabel: entry.sender,
+          }),
+      });
+    }
+
+    const to = kind === "dm" ? `user:${senderId}` : `channel:${channelId}`;
+    const mediaPayload = buildMattermostMediaPayload(mediaList);
+    const commandAuthorized = resolveCommandAuthorizedFromAuthorizers({
+      useAccessGroups: cfg.commands?.useAccessGroups ?? false,
+      authorizers: [],
+    });
+    const ctxPayload = finalizeInboundContext({
+      Body: combinedBody,
+      RawBody: bodyText,
+      CommandBody: bodyText,
+      From:
+        kind === "dm"
+          ? `mattermost:${senderId}`
+          : kind === "group"
+            ? `mattermost:group:${channelId}`
+            : `mattermost:channel:${channelId}`,
+      To: to,
+      SessionKey: sessionKey,
+      ParentSessionKey: threadKeys.parentSessionKey,
+      AccountId: route.accountId,
+      ChatType: chatType,
+      ConversationLabel: fromLabel,
+      GroupSubject: kind !== "dm" ? channelDisplay || roomLabel : undefined,
+      GroupChannel: channelName ? `#${channelName}` : undefined,
+      GroupSpace: teamId,
+      SenderName: senderName,
+      SenderId: senderId,
+      Provider: "mattermost" as const,
+      Surface: "mattermost" as const,
+      MessageSid: post.id ?? undefined,
+      MessageSids: allMessageIds.length > 1 ? allMessageIds : undefined,
+      MessageSidFirst: allMessageIds.length > 1 ? allMessageIds[0] : undefined,
+      MessageSidLast:
+        allMessageIds.length > 1 ? allMessageIds[allMessageIds.length - 1] : undefined,
+      ReplyToId: threadRootId,
+      MessageThreadId: threadRootId,
+      Timestamp: typeof post.create_at === "number" ? post.create_at : undefined,
+      WasMentioned: kind !== "dm" ? effectiveWasMentioned : undefined,
+      CommandAuthorized: commandAuthorized,
+      OriginatingChannel: "mattermost" as const,
+      OriginatingTo: to,
+      ...mediaPayload,
+    });
+
+    if (kind === "dm") {
+      const sessionCfg = cfg.session;
+      const storePath = resolveStorePath(sessionCfg?.store, {
+        agentId: route.agentId,
+      });
+      await updateLastRoute({
+        storePath,
+        sessionKey: route.mainSessionKey,
+        deliveryContext: {
+          channel: "mattermost",
+          to,
+          accountId: route.accountId,
+        },
+      });
+    }
+
+    if (shouldLogVerbose()) {
+      const previewLine = bodyText.slice(0, 200).replace(/\n/g, "\\n");
+      logVerbose(
+        `mattermost inbound: from=${ctxPayload.From} len=${bodyText.length} preview="${previewLine}"`,
+      );
+    }
+
+    const textLimit = resolveTextChunkLimit(cfg, "mattermost", account.accountId, {
+      fallbackLimit: account.textChunkLimit ?? 4000,
+    });
+
+    let prefixContext: ResponsePrefixContext = {
+      identityName: resolveIdentityName(cfg, route.agentId),
+    };
+
+    const { dispatcher, replyOptions, markDispatchIdle } = createReplyDispatcherWithTyping({
+      responsePrefix: resolveEffectiveMessagesConfig(cfg, route.agentId).responsePrefix,
+      responsePrefixContextProvider: () => prefixContext,
+      humanDelay: resolveHumanDelayConfig(cfg, route.agentId),
+      deliver: async (payload: ReplyPayload) => {
+        const mediaUrls = payload.mediaUrls ?? (payload.mediaUrl ? [payload.mediaUrl] : []);
+        const text = payload.text ?? "";
+        if (mediaUrls.length === 0) {
+          const chunks = chunkMarkdownText(text, textLimit);
+          for (const chunk of chunks.length > 0 ? chunks : [text]) {
+            if (!chunk) continue;
+            await sendMessageMattermost(to, chunk, {
+              accountId: account.accountId,
+              replyToId: threadRootId,
+            });
+          }
+        } else {
+          let first = true;
+          for (const mediaUrl of mediaUrls) {
+            const caption = first ? text : "";
+            first = false;
+            await sendMessageMattermost(to, caption, {
+              accountId: account.accountId,
+              mediaUrl,
+              replyToId: threadRootId,
+            });
+          }
+        }
+        runtime.log?.(`delivered reply to ${to}`);
+      },
+      onError: (err, info) => {
+        runtime.error?.(danger(`mattermost ${info.kind} reply failed: ${String(err)}`));
+      },
+      onReplyStart: () => sendTypingIndicator(channelId, threadRootId),
+    });
+
+    await dispatchReplyFromConfig({
+      ctx: ctxPayload,
+      cfg,
+      dispatcher,
+      replyOptions: {
+        ...replyOptions,
+        disableBlockStreaming:
+          typeof account.blockStreaming === "boolean" ? !account.blockStreaming : undefined,
+        onModelSelected: (ctx) => {
+          prefixContext.provider = ctx.provider;
+          prefixContext.model = extractShortModelName(ctx.model);
+          prefixContext.modelFull = `${ctx.provider}/${ctx.model}`;
+          prefixContext.thinkingLevel = ctx.thinkLevel ?? "off";
+        },
+      },
+    });
+    markDispatchIdle();
+    if (historyKey && historyLimit > 0) {
+      clearHistoryEntries({ historyMap: channelHistories, historyKey });
+    }
+  };
+
+  const inboundDebounceMs = resolveInboundDebounceMs({ cfg, channel: "mattermost" });
+  const debouncer = createInboundDebouncer<{
+    post: MattermostPost;
+    payload: MattermostEventPayload;
+  }>({
+    debounceMs: inboundDebounceMs,
+    buildKey: (entry) => {
+      const channelId =
+        entry.post.channel_id ??
+        entry.payload.data?.channel_id ??
+        entry.payload.broadcast?.channel_id;
+      if (!channelId) return null;
+      const threadId = entry.post.root_id?.trim();
+      const threadKey = threadId ? `thread:${threadId}` : "channel";
+      return `mattermost:${account.accountId}:${channelId}:${threadKey}`;
+    },
+    shouldDebounce: (entry) => {
+      if (entry.post.file_ids && entry.post.file_ids.length > 0) return false;
+      const text = entry.post.message?.trim() ?? "";
+      if (!text) return false;
+      return !hasControlCommand(text, cfg);
+    },
+    onFlush: async (entries) => {
+      const last = entries.at(-1);
+      if (!last) return;
+      if (entries.length === 1) {
+        await handlePost(last.post, last.payload);
+        return;
+      }
+      const combinedText = entries
+        .map((entry) => entry.post.message?.trim() ?? "")
+        .filter(Boolean)
+        .join("\n");
+      const mergedPost: MattermostPost = {
+        ...last.post,
+        message: combinedText,
+        file_ids: [],
+      };
+      const ids = entries.map((entry) => entry.post.id).filter(Boolean) as string[];
+      await handlePost(mergedPost, last.payload, ids.length > 0 ? ids : undefined);
+    },
+    onError: (err) => {
+      runtime.error?.(danger(`mattermost debounce flush failed: ${String(err)}`));
+    },
+  });
+
+  const wsUrl = buildMattermostWsUrl(baseUrl);
+  let seq = 1;
+
+  const connectOnce = async (): Promise<void> => {
+    const ws = new WebSocket(wsUrl);
+    const onAbort = () => ws.close();
+    opts.abortSignal?.addEventListener("abort", onAbort, { once: true });
+
+    return await new Promise((resolve) => {
+      ws.on("open", () => {
+        opts.statusSink?.({
+          connected: true,
+          lastConnectedAt: Date.now(),
+          lastError: null,
+        });
+        ws.send(
+          JSON.stringify({
+            seq: seq++,
+            action: "authentication_challenge",
+            data: { token: botToken },
+          }),
+        );
+      });
+
+      ws.on("message", async (data) => {
+        const raw = rawDataToString(data);
+        let payload: MattermostEventPayload;
+        try {
+          payload = JSON.parse(raw) as MattermostEventPayload;
+        } catch {
+          return;
+        }
+        if (payload.event !== "posted") return;
+        const postData = payload.data?.post;
+        if (!postData) return;
+        let post: MattermostPost | null = null;
+        if (typeof postData === "string") {
+          try {
+            post = JSON.parse(postData) as MattermostPost;
+          } catch {
+            return;
+          }
+        } else if (typeof postData === "object") {
+          post = postData as MattermostPost;
+        }
+        if (!post) return;
+        try {
+          await debouncer.enqueue({ post, payload });
+        } catch (err) {
+          runtime.error?.(danger(`mattermost handler failed: ${String(err)}`));
+        }
+      });
+
+      ws.on("close", (code, reason) => {
+        const message = reason.length > 0 ? reason.toString("utf8") : "";
+        opts.statusSink?.({
+          connected: false,
+          lastDisconnect: {
+            at: Date.now(),
+            status: code,
+            error: message || undefined,
+          },
+        });
+        opts.abortSignal?.removeEventListener("abort", onAbort);
+        resolve();
+      });
+
+      ws.on("error", (err) => {
+        runtime.error?.(danger(`mattermost websocket error: ${String(err)}`));
+        opts.statusSink?.({
+          lastError: String(err),
+        });
+      });
+    });
+  };
+
+  while (!opts.abortSignal?.aborted) {
+    await connectOnce();
+    if (opts.abortSignal?.aborted) return;
+    await new Promise((resolve) => setTimeout(resolve, 2000));
+  }
+}
diff --git a/src/mattermost/probe.ts b/src/mattermost/probe.ts
new file mode 100644
index 000000000..c0fa8ae63
--- /dev/null
+++ b/src/mattermost/probe.ts
@@ -0,0 +1,70 @@
+import { normalizeMattermostBaseUrl, type MattermostUser } from "./client.js";
+
+export type MattermostProbe = {
+  ok: boolean;
+  status?: number | null;
+  error?: string | null;
+  elapsedMs?: number | null;
+  bot?: MattermostUser;
+};
+
+async function readMattermostError(res: Response): Promise<string> {
+  const contentType = res.headers.get("content-type") ?? "";
+  if (contentType.includes("application/json")) {
+    const data = (await res.json()) as { message?: string } | undefined;
+    if (data?.message) return data.message;
+    return JSON.stringify(data);
+  }
+  return await res.text();
+}
+
+export async function probeMattermost(
+  baseUrl: string,
+  botToken: string,
+  timeoutMs = 2500,
+): Promise<MattermostProbe> {
+  const normalized = normalizeMattermostBaseUrl(baseUrl);
+  if (!normalized) {
+    return { ok: false, error: "baseUrl missing" };
+  }
+  const url = `${normalized}/api/v4/users/me`;
+  const start = Date.now();
+  const controller = timeoutMs > 0 ? new AbortController() : undefined;
+  let timer: NodeJS.Timeout | null = null;
+  if (controller) {
+    timer = setTimeout(() => controller.abort(), timeoutMs);
+  }
+  try {
+    const res = await fetch(url, {
+      headers: { Authorization: `Bearer ${botToken}` },
+      signal: controller?.signal,
+    });
+    const elapsedMs = Date.now() - start;
+    if (!res.ok) {
+      const detail = await readMattermostError(res);
+      return {
+        ok: false,
+        status: res.status,
+        error: detail || res.statusText,
+        elapsedMs,
+      };
+    }
+    const bot = (await res.json()) as MattermostUser;
+    return {
+      ok: true,
+      status: res.status,
+      elapsedMs,
+      bot,
+    };
+  } catch (err) {
+    const message = err instanceof Error ? err.message : String(err);
+    return {
+      ok: false,
+      status: null,
+      error: message,
+      elapsedMs: Date.now() - start,
+    };
+  } finally {
+    if (timer) clearTimeout(timer);
+  }
+}
diff --git a/src/mattermost/send.ts b/src/mattermost/send.ts
new file mode 100644
index 000000000..40f038cc0
--- /dev/null
+++ b/src/mattermost/send.ts
@@ -0,0 +1,207 @@
+import { loadConfig } from "../config/config.js";
+import { logVerbose, shouldLogVerbose } from "../globals.js";
+import { recordChannelActivity } from "../infra/channel-activity.js";
+import { loadWebMedia } from "../web/media.js";
+import { resolveMattermostAccount } from "./accounts.js";
+import {
+  createMattermostClient,
+  createMattermostDirectChannel,
+  createMattermostPost,
+  fetchMattermostMe,
+  fetchMattermostUserByUsername,
+  normalizeMattermostBaseUrl,
+  uploadMattermostFile,
+  type MattermostUser,
+} from "./client.js";
+
+export type MattermostSendOpts = {
+  botToken?: string;
+  baseUrl?: string;
+  accountId?: string;
+  mediaUrl?: string;
+  replyToId?: string;
+};
+
+export type MattermostSendResult = {
+  messageId: string;
+  channelId: string;
+};
+
+type MattermostTarget =
+  | { kind: "channel"; id: string }
+  | { kind: "user"; id?: string; username?: string };
+
+const botUserCache = new Map<string, MattermostUser>();
+const userByNameCache = new Map<string, MattermostUser>();
+
+function cacheKey(baseUrl: string, token: string): string {
+  return `${baseUrl}::${token}`;
+}
+
+function normalizeMessage(text: string, mediaUrl?: string): string {
+  const trimmed = text.trim();
+  const media = mediaUrl?.trim();
+  return [trimmed, media].filter(Boolean).join("\n");
+}
+
+function isHttpUrl(value: string): boolean {
+  return /^https?:\/\//i.test(value);
+}
+
+function parseMattermostTarget(raw: string): MattermostTarget {
+  const trimmed = raw.trim();
+  if (!trimmed) throw new Error("Recipient is required for Mattermost sends");
+  const lower = trimmed.toLowerCase();
+  if (lower.startsWith("channel:")) {
+    const id = trimmed.slice("channel:".length).trim();
+    if (!id) throw new Error("Channel id is required for Mattermost sends");
+    return { kind: "channel", id };
+  }
+  if (lower.startsWith("user:")) {
+    const id = trimmed.slice("user:".length).trim();
+    if (!id) throw new Error("User id is required for Mattermost sends");
+    return { kind: "user", id };
+  }
+  if (lower.startsWith("mattermost:")) {
+    const id = trimmed.slice("mattermost:".length).trim();
+    if (!id) throw new Error("User id is required for Mattermost sends");
+    return { kind: "user", id };
+  }
+  if (trimmed.startsWith("@")) {
+    const username = trimmed.slice(1).trim();
+    if (!username) {
+      throw new Error("Username is required for Mattermost sends");
+    }
+    return { kind: "user", username };
+  }
+  return { kind: "channel", id: trimmed };
+}
+
+async function resolveBotUser(baseUrl: string, token: string): Promise<MattermostUser> {
+  const key = cacheKey(baseUrl, token);
+  const cached = botUserCache.get(key);
+  if (cached) return cached;
+  const client = createMattermostClient({ baseUrl, botToken: token });
+  const user = await fetchMattermostMe(client);
+  botUserCache.set(key, user);
+  return user;
+}
+
+async function resolveUserIdByUsername(params: {
+  baseUrl: string;
+  token: string;
+  username: string;
+}): Promise<string> {
+  const { baseUrl, token, username } = params;
+  const key = `${cacheKey(baseUrl, token)}::${username.toLowerCase()}`;
+  const cached = userByNameCache.get(key);
+  if (cached?.id) return cached.id;
+  const client = createMattermostClient({ baseUrl, botToken: token });
+  const user = await fetchMattermostUserByUsername(client, username);
+  userByNameCache.set(key, user);
+  return user.id;
+}
+
+async function resolveTargetChannelId(params: {
+  target: MattermostTarget;
+  baseUrl: string;
+  token: string;
+}): Promise<string> {
+  if (params.target.kind === "channel") return params.target.id;
+  const userId = params.target.id
+    ? params.target.id
+    : await resolveUserIdByUsername({
+        baseUrl: params.baseUrl,
+        token: params.token,
+        username: params.target.username ?? "",
+      });
+  const botUser = await resolveBotUser(params.baseUrl, params.token);
+  const client = createMattermostClient({
+    baseUrl: params.baseUrl,
+    botToken: params.token,
+  });
+  const channel = await createMattermostDirectChannel(client, [botUser.id, userId]);
+  return channel.id;
+}
+
+export async function sendMessageMattermost(
+  to: string,
+  text: string,
+  opts: MattermostSendOpts = {},
+): Promise<MattermostSendResult> {
+  const cfg = loadConfig();
+  const account = resolveMattermostAccount({
+    cfg,
+    accountId: opts.accountId,
+  });
+  const token = opts.botToken?.trim() || account.botToken?.trim();
+  if (!token) {
+    throw new Error(
+      `Mattermost bot token missing for account "${account.accountId}" (set channels.mattermost.accounts.${account.accountId}.botToken or MATTERMOST_BOT_TOKEN for default).`,
+    );
+  }
+  const baseUrl = normalizeMattermostBaseUrl(opts.baseUrl ?? account.baseUrl);
+  if (!baseUrl) {
+    throw new Error(
+      `Mattermost baseUrl missing for account "${account.accountId}" (set channels.mattermost.accounts.${account.accountId}.baseUrl or MATTERMOST_URL for default).`,
+    );
+  }
+
+  const target = parseMattermostTarget(to);
+  const channelId = await resolveTargetChannelId({
+    target,
+    baseUrl,
+    token,
+  });
+
+  const client = createMattermostClient({ baseUrl, botToken: token });
+  let message = text?.trim() ?? "";
+  let fileIds: string[] | undefined;
+  let uploadError: Error | undefined;
+  const mediaUrl = opts.mediaUrl?.trim();
+  if (mediaUrl) {
+    try {
+      const media = await loadWebMedia(mediaUrl);
+      const fileInfo = await uploadMattermostFile(client, {
+        channelId,
+        buffer: media.buffer,
+        fileName: media.fileName ?? "upload",
+        contentType: media.contentType ?? undefined,
+      });
+      fileIds = [fileInfo.id];
+    } catch (err) {
+      uploadError = err instanceof Error ? err : new Error(String(err));
+      if (shouldLogVerbose()) {
+        logVerbose(
+          `mattermost send: media upload failed, falling back to URL text: ${String(err)}`,
+        );
+      }
+      message = normalizeMessage(message, isHttpUrl(mediaUrl) ? mediaUrl : "");
+    }
+  }
+
+  if (!message && (!fileIds || fileIds.length === 0)) {
+    if (uploadError) {
+      throw new Error(`Mattermost media upload failed: ${uploadError.message}`);
+    }
+    throw new Error("Mattermost message is empty");
+  }
+
+  const post = await createMattermostPost(client, {
+    channelId,
+    message,
+    rootId: opts.replyToId,
+    fileIds,
+  });
+
+  recordChannelActivity({
+    channel: "mattermost",
+    accountId: account.accountId,
+    direction: "outbound",
+  });
+
+  return {
+    messageId: post.id ?? "unknown",
+    channelId,
+  };
+}
diff --git a/src/plugin-sdk/index.ts b/src/plugin-sdk/index.ts
index 8bef1da37..62979bdd1 100644
--- a/src/plugin-sdk/index.ts
+++ b/src/plugin-sdk/index.ts
@@ -81,6 +81,7 @@ export type {
 export {
   DiscordConfigSchema,
   IMessageConfigSchema,
+  MattermostConfigSchema,
   MSTeamsConfigSchema,
   SignalConfigSchema,
   SlackConfigSchema,
@@ -120,6 +121,7 @@ export {
   resolveBlueBubblesGroupRequireMention,
   resolveDiscordGroupRequireMention,
   resolveIMessageGroupRequireMention,
+  resolveMattermostGroupRequireMention,
   resolveSlackGroupRequireMention,
   resolveTelegramGroupRequireMention,
   resolveWhatsAppGroupRequireMention,
@@ -236,6 +238,21 @@ export {
   normalizeSlackMessagingTarget,
 } from "../channels/plugins/normalize/slack.js";
 
+// Channel: Mattermost
+export {
+  listEnabledMattermostAccounts,
+  listMattermostAccountIds,
+  resolveDefaultMattermostAccountId,
+  resolveMattermostAccount,
+  type ResolvedMattermostAccount,
+} from "../mattermost/accounts.js";
+export { normalizeMattermostBaseUrl } from "../mattermost/client.js";
+export { mattermostOnboardingAdapter } from "../channels/plugins/onboarding/mattermost.js";
+export {
+  looksLikeMattermostTargetId,
+  normalizeMattermostMessagingTarget,
+} from "../channels/plugins/normalize/mattermost.js";
+
 // Channel: Telegram
 export {
   listTelegramAccountIds,
diff --git a/src/plugins/runtime/index.ts b/src/plugins/runtime/index.ts
index 4765c71c7..e564ad2f8 100644
--- a/src/plugins/runtime/index.ts
+++ b/src/plugins/runtime/index.ts
@@ -57,6 +57,9 @@ import { enqueueSystemEvent } from "../../infra/system-events.js";
 import { monitorIMessageProvider } from "../../imessage/monitor.js";
 import { probeIMessage } from "../../imessage/probe.js";
 import { sendMessageIMessage } from "../../imessage/send.js";
+import { monitorMattermostProvider } from "../../mattermost/monitor.js";
+import { probeMattermost } from "../../mattermost/probe.js";
+import { sendMessageMattermost } from "../../mattermost/send.js";
 import { shouldLogVerbose } from "../../globals.js";
 import { getChildLogger } from "../../logging.js";
 import { normalizeLogLevel } from "../../logging/levels.js";
@@ -230,6 +233,11 @@ export function createPluginRuntime(): PluginRuntime {
         monitorSlackProvider,
         handleSlackAction,
       },
+      mattermost: {
+        probeMattermost,
+        sendMessageMattermost,
+        monitorMattermostProvider,
+      },
       telegram: {
         auditGroupMembership: auditTelegramGroupMembership,
         collectUnmentionedGroupIds: collectTelegramUnmentionedGroupIds,
diff --git a/src/plugins/runtime/types.ts b/src/plugins/runtime/types.ts
index 089e20c37..31350693c 100644
--- a/src/plugins/runtime/types.ts
+++ b/src/plugins/runtime/types.ts
@@ -98,6 +98,10 @@ type ResolveSlackUserAllowlist =
 type SendMessageSlack = typeof import("../../slack/send.js").sendMessageSlack;
 type MonitorSlackProvider = typeof import("../../slack/index.js").monitorSlackProvider;
 type HandleSlackAction = typeof import("../../agents/tools/slack-actions.js").handleSlackAction;
+type ProbeMattermost = typeof import("../../mattermost/probe.js").probeMattermost;
+type SendMessageMattermost = typeof import("../../mattermost/send.js").sendMessageMattermost;
+type MonitorMattermostProvider =
+  typeof import("../../mattermost/monitor.js").monitorMattermostProvider;
 type AuditTelegramGroupMembership =
   typeof import("../../telegram/audit.js").auditTelegramGroupMembership;
 type CollectTelegramUnmentionedGroupIds =
@@ -242,6 +246,11 @@ export type PluginRuntime = {
       monitorSlackProvider: MonitorSlackProvider;
       handleSlackAction: HandleSlackAction;
     };
+    mattermost: {
+      probeMattermost: ProbeMattermost;
+      sendMessageMattermost: SendMessageMattermost;
+      monitorMattermostProvider: MonitorMattermostProvider;
+    };
     telegram: {
       auditGroupMembership: AuditTelegramGroupMembership;
       collectUnmentionedGroupIds: CollectTelegramUnmentionedGroupIds;
diff --git a/src/utils/message-channel.ts b/src/utils/message-channel.ts
index ecd1f713b..c09436ac8 100644
--- a/src/utils/message-channel.ts
+++ b/src/utils/message-channel.ts
@@ -22,6 +22,7 @@ const MARKDOWN_CAPABLE_CHANNELS = new Set<string>([
   "telegram",
   "signal",
   "discord",
+  "mattermost",
   "tui",
   INTERNAL_MESSAGE_CHANNEL,
 ]);
diff --git a/ui/src/ui/types.ts b/ui/src/ui/types.ts
index 6cdbfb029..aaf89b9e9 100644
--- a/ui/src/ui/types.ts
+++ b/ui/src/ui/types.ts
@@ -164,6 +164,39 @@ export type SlackStatus = {
   lastProbeAt?: number | null;
 };
 
+export type MattermostBot = {
+  id?: string | null;
+  username?: string | null;
+};
+
+export type MattermostProbe = {
+  ok: boolean;
+  status?: number | null;
+  error?: string | null;
+  elapsedMs?: number | null;
+  bot?: MattermostBot | null;
+};
+
+export type MattermostStatus = {
+  configured: boolean;
+  botTokenSource?: string | null;
+  running: boolean;
+  connected?: boolean | null;
+  lastConnectedAt?: number | null;
+  lastDisconnect?: {
+    at: number;
+    status?: number | null;
+    error?: string | null;
+    loggedOut?: boolean | null;
+  } | null;
+  lastStartAt?: number | null;
+  lastStopAt?: number | null;
+  lastError?: string | null;
+  baseUrl?: string | null;
+  probe?: MattermostProbe | null;
+  lastProbeAt?: number | null;
+};
+
 export type SignalProbe = {
   ok: boolean;
   status?: number | null;
@@ -363,6 +396,7 @@ export type CronPayload =
         | "telegram"
         | "discord"
         | "slack"
+        | "mattermost"
         | "signal"
         | "imessage"
         | "msteams";
diff --git a/ui/src/ui/views/channels.mattermost.ts b/ui/src/ui/views/channels.mattermost.ts
new file mode 100644
index 000000000..c2513ed44
--- /dev/null
+++ b/ui/src/ui/views/channels.mattermost.ts
@@ -0,0 +1,70 @@
+import { html, nothing } from "lit";
+
+import { formatAgo } from "../format";
+import type { MattermostStatus } from "../types";
+import type { ChannelsProps } from "./channels.types";
+import { renderChannelConfigSection } from "./channels.config";
+
+export function renderMattermostCard(params: {
+  props: ChannelsProps;
+  mattermost?: MattermostStatus | null;
+  accountCountLabel: unknown;
+}) {
+  const { props, mattermost, accountCountLabel } = params;
+
+  return html`
+    <div class="card">
+      <div class="card-title">Mattermost</div>
+      <div class="card-sub">Bot token + WebSocket status and configuration.</div>
+      ${accountCountLabel}
+
+      <div class="status-list" style="margin-top: 16px;">
+        <div>
+          <span class="label">Configured</span>
+          <span>${mattermost?.configured ? "Yes" : "No"}</span>
+        </div>
+        <div>
+          <span class="label">Running</span>
+          <span>${mattermost?.running ? "Yes" : "No"}</span>
+        </div>
+        <div>
+          <span class="label">Connected</span>
+          <span>${mattermost?.connected ? "Yes" : "No"}</span>
+        </div>
+        <div>
+          <span class="label">Base URL</span>
+          <span>${mattermost?.baseUrl || "n/a"}</span>
+        </div>
+        <div>
+          <span class="label">Last start</span>
+          <span>${mattermost?.lastStartAt ? formatAgo(mattermost.lastStartAt) : "n/a"}</span>
+        </div>
+        <div>
+          <span class="label">Last probe</span>
+          <span>${mattermost?.lastProbeAt ? formatAgo(mattermost.lastProbeAt) : "n/a"}</span>
+        </div>
+      </div>
+
+      ${mattermost?.lastError
+        ? html`<div class="callout danger" style="margin-top: 12px;">
+            ${mattermost.lastError}
+          </div>`
+        : nothing}
+
+      ${mattermost?.probe
+        ? html`<div class="callout" style="margin-top: 12px;">
+            Probe ${mattermost.probe.ok ? "ok" : "failed"} -
+            ${mattermost.probe.status ?? ""} ${mattermost.probe.error ?? ""}
+          </div>`
+        : nothing}
+
+      ${renderChannelConfigSection({ channelId: "mattermost", props })}
+
+      <div class="row" style="margin-top: 12px;">
+        <button class="btn" @click=${() => props.onRefresh(true)}>
+          Probe
+        </button>
+      </div>
+    </div>
+  `;
+}
diff --git a/ui/src/ui/views/channels.ts b/ui/src/ui/views/channels.ts
index 232cf2c85..96a6b8556 100644
--- a/ui/src/ui/views/channels.ts
+++ b/ui/src/ui/views/channels.ts
@@ -7,6 +7,7 @@ import type {
   ChannelsStatusSnapshot,
   DiscordStatus,
   IMessageStatus,
+  MattermostStatus,
   NostrProfile,
   NostrStatus,
   SignalStatus,
@@ -23,6 +24,7 @@ import { channelEnabled, renderChannelAccountCount } from "./channels.shared";
 import { renderChannelConfigSection } from "./channels.config";
 import { renderDiscordCard } from "./channels.discord";
 import { renderIMessageCard } from "./channels.imessage";
+import { renderMattermostCard } from "./channels.mattermost";
 import { renderNostrCard } from "./channels.nostr";
 import { renderSignalCard } from "./channels.signal";
 import { renderSlackCard } from "./channels.slack";
@@ -39,6 +41,7 @@ export function renderChannels(props: ChannelsProps) {
     | undefined;
   const discord = (channels?.discord ?? null) as DiscordStatus | null;
   const slack = (channels?.slack ?? null) as SlackStatus | null;
+  const mattermost = (channels?.mattermost ?? null) as MattermostStatus | null;
   const signal = (channels?.signal ?? null) as SignalStatus | null;
   const imessage = (channels?.imessage ?? null) as IMessageStatus | null;
   const nostr = (channels?.nostr ?? null) as NostrStatus | null;
@@ -62,6 +65,7 @@ export function renderChannels(props: ChannelsProps) {
           telegram,
           discord,
           slack,
+          mattermost,
           signal,
           imessage,
           nostr,
@@ -97,7 +101,7 @@ function resolveChannelOrder(snapshot: ChannelsStatusSnapshot | null): ChannelKe
   if (snapshot?.channelOrder?.length) {
     return snapshot.channelOrder;
   }
-  return ["whatsapp", "telegram", "discord", "slack", "signal", "imessage", "nostr"];
+  return ["whatsapp", "telegram", "discord", "slack", "mattermost", "signal", "imessage", "nostr"];
 }
 
 function renderChannel(
@@ -135,6 +139,12 @@ function renderChannel(
         slack: data.slack,
         accountCountLabel,
       });
+    case "mattermost":
+      return renderMattermostCard({
+        props,
+        mattermost: data.mattermost,
+        accountCountLabel,
+      });
     case "signal":
       return renderSignalCard({
         props,
diff --git a/ui/src/ui/views/channels.types.ts b/ui/src/ui/views/channels.types.ts
index 43576d54a..d3a98d44e 100644
--- a/ui/src/ui/views/channels.types.ts
+++ b/ui/src/ui/views/channels.types.ts
@@ -4,6 +4,7 @@ import type {
   ConfigUiHints,
   DiscordStatus,
   IMessageStatus,
+  MattermostStatus,
   NostrProfile,
   NostrStatus,
   SignalStatus,
@@ -53,6 +54,7 @@ export type ChannelsChannelData = {
   telegram?: TelegramStatus;
   discord?: DiscordStatus | null;
   slack?: SlackStatus | null;
+  mattermost?: MattermostStatus | null;
   signal?: SignalStatus | null;
   imessage?: IMessageStatus | null;
   nostr?: NostrStatus | null;