feat: standardize timestamps to UTC

CHANGELOG.md

@@ -4,6 +4,9 @@
 
 ## Unreleased
 
+### Breaking
+- Timestamps in agent envelopes are now UTC (compact `YYYY-MM-DDTHH:mmZ`); removed `messages.timestampPrefix`. Add `agent.userTimezone` to tell the model the user’s local time (system prompt only).
+
 ### Fixes
 - Onboarding: resolve CLI entrypoint when running via `npx` so gateway daemon install works without a build step.
 - Linux: auto-attempt lingering during onboarding (try without sudo, fallback to sudo) and prompt on install/restart to keep the gateway alive after logout/idle. Thanks @tobiasbischoff for PR #237.

docs/configuration.md

@@ -432,16 +432,26 @@ Default: `~/clawd`.
 If `agent.sandbox` is enabled, non-main sessions can override this with their
 own per-session workspaces under `agent.sandbox.workspaceRoot`.
 
+### `agent.userTimezone`
+
+Sets the user’s timezone for **system prompt context** (not for timestamps in
+message envelopes). If unset, Clawdbot uses the host timezone at runtime.
+
+```json5
+{
+  agent: { userTimezone: "America/Chicago" }
+}
+```
+
 ### `messages`
 
-Controls inbound/outbound prefixes and timestamps.
+Controls inbound/outbound prefixes.
 
 ```json5
 {
   messages: {
     messagePrefix: "[clawdbot]",
-    responsePrefix: "🦞",
-    timestampPrefix: "Europe/London"
+    responsePrefix: "🦞"
   }
 }
 ```

docs/timezone.md

@@ -0,0 +1,40 @@
+---
+summary: "Timezone handling for agents, envelopes, and prompts"
+read_when:
+  - You need to understand how timestamps are normalized for the model
+  - Configuring the user timezone for system prompts
+---
+
+# Timezones
+
+Clawdbot standardizes timestamps so the model sees a **single reference time**.
+
+## Message envelopes (UTC)
+
+Inbound messages are wrapped in an envelope like:
+
+```
+[Surface ... 2026-01-05T21:26Z] message text
+```
+
+The timestamp in the envelope is **always UTC**, with minutes precision.
+
+## Tool payloads (raw provider data)
+
+Tool calls (`discord.readMessages`, `slack.readMessages`, etc.) return **raw provider timestamps**.
+These are typically UTC ISO strings (Discord) or UTC epoch strings (Slack). We do not rewrite them.
+
+## User timezone for the system prompt
+
+Set `agent.userTimezone` to tell the model the user's local time zone. If it is
+unset, Clawdbot resolves the **host timezone at runtime** (no config write).
+
+```json5
+{
+  agent: { userTimezone: "America/Chicago" }
+}
+```
+
+The system prompt includes:
+- `User timezone: America/Chicago`
+- `Current user time: 2026-01-05 15:26`

src/agents/pi-embedded-runner.ts

@@ -116,6 +116,46 @@ function resolveGlobalLane(lane?: string) {
   return cleaned ? cleaned : "main";
 }
 
+function resolveUserTimezone(configured?: string): string {
+  const trimmed = configured?.trim();
+  if (trimmed) {
+    try {
+      new Intl.DateTimeFormat("en-US", { timeZone: trimmed }).format(
+        new Date(),
+      );
+      return trimmed;
+    } catch {
+      // ignore invalid timezone
+    }
+  }
+  const host = Intl.DateTimeFormat().resolvedOptions().timeZone;
+  return host?.trim() || "UTC";
+}
+
+function formatUserTime(date: Date, timeZone: string): string | undefined {
+  try {
+    const parts = new Intl.DateTimeFormat("en-CA", {
+      timeZone,
+      year: "numeric",
+      month: "2-digit",
+      day: "2-digit",
+      hour: "2-digit",
+      minute: "2-digit",
+      hourCycle: "h23",
+    }).formatToParts(date);
+    const map: Record<string, string> = {};
+    for (const part of parts) {
+      if (part.type !== "literal") map[part.type] = part.value;
+    }
+    if (!map.year || !map.month || !map.day || !map.hour || !map.minute) {
+      return undefined;
+    }
+    return `${map.year}-${map.month}-${map.day} ${map.hour}:${map.minute}`;
+  } catch {
+    return undefined;
+  }
+}
+
 export function buildEmbeddedSandboxInfo(
   sandbox?: Awaited<ReturnType<typeof resolveSandboxContext>>,
 ): EmbeddedSandboxInfo | undefined {
@@ -398,6 +438,10 @@ export async function runEmbeddedPiAgent(params: {
           };
           const sandboxInfo = buildEmbeddedSandboxInfo(sandbox);
           const reasoningTagHint = provider === "ollama";
+          const userTimezone = resolveUserTimezone(
+            params.config?.agent?.userTimezone,
+          );
+          const userTime = formatUserTime(new Date(), userTimezone);
           const systemPrompt = buildSystemPrompt({
             appendPrompt: buildAgentSystemPromptAppend({
               workspaceDir: resolvedWorkspace,
@@ -408,6 +452,8 @@ export async function runEmbeddedPiAgent(params: {
               runtimeInfo,
               sandboxInfo,
               toolNames: tools.map((tool) => tool.name),
+              userTimezone,
+              userTime,
             }),
             contextFiles,
             skills: promptSkills,

src/agents/system-prompt.test.ts

@@ -46,4 +46,16 @@ describe("buildAgentSystemPromptAppend", () => {
     expect(prompt).toContain("sessions_send");
     expect(prompt).toContain("Unavailable tools (do not call):");
   });
+
+  it("includes user time when provided", () => {
+    const prompt = buildAgentSystemPromptAppend({
+      workspaceDir: "/tmp/clawd",
+      userTimezone: "America/Chicago",
+      userTime: "2026-01-05 15:26",
+    });
+
+    expect(prompt).toContain("## Time");
+    expect(prompt).toContain("User timezone: America/Chicago");
+    expect(prompt).toContain("Current user time: 2026-01-05 15:26");
+  });
 });

src/agents/system-prompt.ts

@@ -7,6 +7,8 @@ export function buildAgentSystemPromptAppend(params: {
   ownerNumbers?: string[];
   reasoningTagHint?: boolean;
   toolNames?: string[];
+  userTimezone?: string;
+  userTime?: string;
   runtimeInfo?: {
     host?: string;
     os?: string;
@@ -109,6 +111,8 @@ export function buildAgentSystemPromptAppend(params: {
         "<final>Hey there! What would you like to do next?</final>",
       ].join(" ")
     : undefined;
+  const userTimezone = params.userTimezone?.trim();
+  const userTime = params.userTime?.trim();
   const runtimeInfo = params.runtimeInfo;
   const runtimeLines: string[] = [];
   if (runtimeInfo?.host) runtimeLines.push(`Host: ${runtimeInfo.host}`);
@@ -182,6 +186,10 @@ export function buildAgentSystemPromptAppend(params: {
     "Never send streaming/partial replies to external messaging surfaces; only final replies should be delivered there.",
     "Clawdbot handles message transport automatically; respond normally and your reply will be delivered to the current chat.",
     "",
+    userTimezone || userTime ? "## Time" : "",
+    userTimezone ? `User timezone: ${userTimezone}` : "",
+    userTime ? `Current user time: ${userTime}` : "",
+    userTimezone || userTime ? "" : "",
     "## Reply Tags",
     "To request a native reply/quote on supported surfaces, include one tag in your reply:",
     "- [[reply_to_current]] replies to the triggering message.",

src/auto-reply/envelope.test.ts

@@ -19,12 +19,12 @@ describe("formatAgentEnvelope", () => {
 
     process.env.TZ = originalTz;
 
-    expect(body).toMatch(
-      /^\[WebChat user1 mac-mini 10\.0\.0\.5 2025-01-02T03:04\+00:00\{.+\}\] hello$/,
+    expect(body).toBe(
+      "[WebChat user1 mac-mini 10.0.0.5 2025-01-02T03:04Z] hello",
     );
   });
 
-  it("formats timestamps in local time (not UTC)", () => {
+  it("formats timestamps in UTC regardless of local timezone", () => {
     const originalTz = process.env.TZ;
     process.env.TZ = "America/Los_Angeles";
 
@@ -37,9 +37,7 @@ describe("formatAgentEnvelope", () => {
 
     process.env.TZ = originalTz;
 
-    expect(body).toBe(
-      "[WebChat 2025-01-01T19:04-08:00{America/Los_Angeles}] hello",
-    );
+    expect(body).toBe("[WebChat 2025-01-02T03:04Z] hello");
   });
 
   it("handles missing optional fields", () => {

src/auto-reply/envelope.ts

@@ -12,25 +12,15 @@ function formatTimestamp(ts?: number | Date): string | undefined {
   const date = ts instanceof Date ? ts : new Date(ts);
   if (Number.isNaN(date.getTime())) return undefined;
 
-  const yyyy = String(date.getFullYear()).padStart(4, "0");
-  const mm = String(date.getMonth() + 1).padStart(2, "0");
-  const dd = String(date.getDate()).padStart(2, "0");
-  const hh = String(date.getHours()).padStart(2, "0");
-  const min = String(date.getMinutes()).padStart(2, "0");
+  const yyyy = String(date.getUTCFullYear()).padStart(4, "0");
+  const mm = String(date.getUTCMonth() + 1).padStart(2, "0");
+  const dd = String(date.getUTCDate()).padStart(2, "0");
+  const hh = String(date.getUTCHours()).padStart(2, "0");
+  const min = String(date.getUTCMinutes()).padStart(2, "0");
 
-  // getTimezoneOffset() is minutes *behind* UTC. Flip sign to get ISO offset.
-  const offsetMinutes = -date.getTimezoneOffset();
-  const sign = offsetMinutes >= 0 ? "+" : "-";
-  const absOffsetMinutes = Math.abs(offsetMinutes);
-  const offsetH = String(Math.floor(absOffsetMinutes / 60)).padStart(2, "0");
-  const offsetM = String(absOffsetMinutes % 60).padStart(2, "0");
-
-  const tz = Intl.DateTimeFormat().resolvedOptions().timeZone;
-  const tzSuffix = tz ? `{${tz}}` : "";
-
-  // Compact ISO-like *local* timestamp with minutes precision.
-  // Example: 2025-01-02T03:04-08:00{America/Los_Angeles}
-  return `${yyyy}-${mm}-${dd}T${hh}:${min}${sign}${offsetH}:${offsetM}${tzSuffix}`;
+  // Compact ISO-like UTC timestamp with minutes precision.
+  // Example: 2025-01-02T03:04Z
+  return `${yyyy}-${mm}-${dd}T${hh}:${min}Z`;
 }
 
 export function formatAgentEnvelope(params: AgentEnvelopeParams): string {

src/config/types.ts

@@ -445,7 +445,6 @@ export type RoutingConfig = {
 export type MessagesConfig = {
   messagePrefix?: string; // Prefix added to all inbound messages (default: "[clawdbot]" if no allowFrom, else "")
   responsePrefix?: string; // Prefix auto-added to all outbound replies (e.g., "🦞")
-  timestampPrefix?: boolean | string; // true/false or IANA timezone string (default: true with UTC)
 };
 
 export type BridgeBindMode = "auto" | "lan" | "tailnet" | "loopback";
@@ -672,6 +671,8 @@ export type ClawdbotConfig = {
     imageModel?: string;
     /** Agent working directory (preferred). Used as the default cwd for agent runs. */
     workspace?: string;
+    /** Optional IANA timezone for the user (used in system prompt; defaults to host timezone). */
+    userTimezone?: string;
     /** Optional allowlist for /model (provider/model or model-only). */
     allowedModels?: string[];
     /** Optional model aliases for /model (alias -> provider/model). */

src/config/zod-schema.ts

@@ -150,7 +150,6 @@ const MessagesSchema = z
   .object({
     messagePrefix: z.string().optional(),
     responsePrefix: z.string().optional(),
-    timestampPrefix: z.union([z.boolean(), z.string()]).optional(),
   })
   .optional();
 
@@ -376,6 +375,7 @@ export const ClawdbotSchema = z.object({
       model: z.string().optional(),
       imageModel: z.string().optional(),
       workspace: z.string().optional(),
+      userTimezone: z.string().optional(),
       allowedModels: z.array(z.string()).optional(),
       modelAliases: z.record(z.string(), z.string()).optional(),
       modelFallbacks: z.array(z.string()).optional(),

src/telegram/bot.test.ts

@@ -101,7 +101,7 @@ describe("createTelegramBot", () => {
       expect(replySpy).toHaveBeenCalledTimes(1);
       const payload = replySpy.mock.calls[0][0];
       expect(payload.Body).toMatch(
-        /^\[Telegram Ada Lovelace \(@ada_bot\) id:1234 2025-01-09T01:00\+01:00\{Europe\/Vienna\}\]/,
+        /^\[Telegram Ada Lovelace \(@ada_bot\) id:1234 2025-01-09T00:00Z\]/,
       );
       expect(payload.Body).toContain("hello world");
     } finally {

src/web/auto-reply.test.ts

@@ -465,9 +465,6 @@ describe("web auto-reply", () => {
       };
 
       setLoadConfigMock(() => ({
-        messages: {
-          timestampPrefix: "UTC",
-        },
         session: { store: store.storePath },
       }));
 
@@ -500,11 +497,11 @@ describe("web auto-reply", () => {
       const firstArgs = resolver.mock.calls[0][0];
       const secondArgs = resolver.mock.calls[1][0];
       expect(firstArgs.Body).toContain(
-        "[WhatsApp +1 2025-01-01T01:00+01:00{Europe/Vienna}] [clawdbot] first",
+        "[WhatsApp +1 2025-01-01T00:00Z] [clawdbot] first",
       );
       expect(firstArgs.Body).not.toContain("second");
       expect(secondArgs.Body).toContain(
-        "[WhatsApp +1 2025-01-01T02:00+01:00{Europe/Vienna}] [clawdbot] second",
+        "[WhatsApp +1 2025-01-01T01:00Z] [clawdbot] second",
       );
       expect(secondArgs.Body).not.toContain("first");
 
@@ -1350,7 +1347,6 @@ describe("web auto-reply", () => {
       messages: {
         messagePrefix: "[same-phone]",
         responsePrefix: undefined,
-        timestampPrefix: false,
       },
     }));
 
@@ -1475,7 +1471,6 @@ describe("web auto-reply", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: "🦞",
-        timestampPrefix: false,
       },
     }));
 
@@ -1520,7 +1515,6 @@ describe("web auto-reply", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: "🦞",
-        timestampPrefix: false,
       },
     }));
 
@@ -1565,7 +1559,6 @@ describe("web auto-reply", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: "🦞",
-        timestampPrefix: false,
       },
     }));
 
@@ -1611,7 +1604,6 @@ describe("web auto-reply", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: "🦞",
-        timestampPrefix: false,
       },
     }));
 

src/web/inbound.media.test.ts

@@ -16,7 +16,6 @@ vi.mock("../config/config.js", async (importOriginal) => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: undefined,
-        timestampPrefix: false,
       },
     }),
   };

src/web/monitor-inbox.test.ts

@@ -16,7 +16,6 @@ const mockLoadConfig = vi.fn().mockReturnValue({
   messages: {
     messagePrefix: undefined,
     responsePrefix: undefined,
-    timestampPrefix: false,
   },
 });
 
@@ -480,7 +479,6 @@ describe("web monitor inbox", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: undefined,
-        timestampPrefix: false,
       },
     });
 
@@ -536,7 +534,6 @@ describe("web monitor inbox", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: undefined,
-        timestampPrefix: false,
       },
     });
 
@@ -576,7 +573,6 @@ describe("web monitor inbox", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: undefined,
-        timestampPrefix: false,
       },
     });
 
@@ -592,7 +588,6 @@ describe("web monitor inbox", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: undefined,
-        timestampPrefix: false,
       },
     });
 
@@ -628,7 +623,6 @@ describe("web monitor inbox", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: undefined,
-        timestampPrefix: false,
       },
     });
 
@@ -643,7 +637,6 @@ describe("web monitor inbox", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: undefined,
-        timestampPrefix: false,
       },
     });
 
@@ -685,7 +678,6 @@ describe("web monitor inbox", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: undefined,
-        timestampPrefix: false,
       },
     });
 
@@ -720,7 +712,6 @@ describe("web monitor inbox", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: undefined,
-        timestampPrefix: false,
       },
     });
 
@@ -737,7 +728,6 @@ describe("web monitor inbox", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: undefined,
-        timestampPrefix: false,
       },
     });
 
@@ -773,7 +763,6 @@ describe("web monitor inbox", () => {
       messages: {
         messagePrefix: undefined,
         responsePrefix: undefined,
-        timestampPrefix: false,
       },
     });
 
@@ -840,7 +829,6 @@ it("defaults to self-only when no config is present", async () => {
     messages: {
       messagePrefix: undefined,
       responsePrefix: undefined,
-      timestampPrefix: false,
     },
   });
 

src/web/test-helpers.ts

@@ -13,7 +13,6 @@ const DEFAULT_CONFIG = {
   messages: {
     messagePrefix: undefined,
     responsePrefix: undefined,
-    timestampPrefix: false,
   },
 };