diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0d526e1cf..1b1b4c7dd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -47,6 +47,7 @@
 - Discord: stop provider when gateway reconnects are exhausted and surface errors. (#514) — thanks @joshp123
 - Agents: strip empty assistant text blocks from session history to avoid Claude API 400s. (#210)
 - Agents: scrub unsupported JSON Schema keywords from tool schemas for Cloud Code Assist API compatibility. (#567) — thanks @erikpr1994
+- Agents: simplify session tool schemas for Gemini compatibility. (#599) — thanks @mcinteerj
 - Auto-reply: preserve block reply ordering with timeout fallback for streaming. (#503) — thanks @joshp123
 - Auto-reply: block reply ordering fix (duplicate PR superseded by #503). (#483) — thanks @AbhisekBasu1
 - Auto-reply: avoid splitting outbound chunks inside parentheses. (#499) — thanks @philipp-spiess
diff --git a/src/agents/clawdbot-tools.sessions.test.ts b/src/agents/clawdbot-tools.sessions.test.ts
index c7df1cf79..1f34ff957 100644
--- a/src/agents/clawdbot-tools.sessions.test.ts
+++ b/src/agents/clawdbot-tools.sessions.test.ts
@@ -23,6 +23,43 @@ vi.mock("../config/config.js", async (importOriginal) => {
 import { createClawdbotTools } from "./clawdbot-tools.js";
 
 describe("sessions tools", () => {
+  it("uses number (not integer) in tool schemas for Gemini compatibility", () => {
+    const tools = createClawdbotTools();
+    const byName = (name: string) => {
+      const tool = tools.find((candidate) => candidate.name === name);
+      expect(tool).toBeDefined();
+      if (!tool) throw new Error(`missing ${name} tool`);
+      return tool;
+    };
+
+    const schemaProp = (toolName: string, prop: string) => {
+      const tool = byName(toolName);
+      const schema = tool.parameters as {
+        anyOf?: unknown;
+        oneOf?: unknown;
+        properties?: Record<string, unknown>;
+      };
+      expect(schema.anyOf).toBeUndefined();
+      expect(schema.oneOf).toBeUndefined();
+
+      const properties = schema.properties ?? {};
+      const value = properties[prop] as { type?: unknown } | undefined;
+      expect(value).toBeDefined();
+      if (!value) throw new Error(`missing ${toolName} schema prop: ${prop}`);
+      return value;
+    };
+
+    expect(schemaProp("sessions_history", "limit").type).toBe("number");
+    expect(schemaProp("sessions_list", "limit").type).toBe("number");
+    expect(schemaProp("sessions_list", "activeMinutes").type).toBe("number");
+    expect(schemaProp("sessions_list", "messageLimit").type).toBe("number");
+    expect(schemaProp("sessions_send", "timeoutSeconds").type).toBe("number");
+    expect(schemaProp("sessions_spawn", "runTimeoutSeconds").type).toBe(
+      "number",
+    );
+    expect(schemaProp("sessions_spawn", "timeoutSeconds").type).toBe("number");
+  });
+
   it("sessions_list filters kinds and includes messages", async () => {
     callGatewayMock.mockReset();
     callGatewayMock.mockImplementation(async (opts: unknown) => {
diff --git a/src/agents/tools/sessions-send-tool.ts b/src/agents/tools/sessions-send-tool.ts
index 7640d314b..cce894d44 100644
--- a/src/agents/tools/sessions-send-tool.ts
+++ b/src/agents/tools/sessions-send-tool.ts
@@ -32,8 +32,10 @@ import {
 
 const SessionsSendToolSchema = Type.Object({
   sessionKey: Type.Optional(Type.String()),
-  label: Type.Optional(Type.String()),
-  agentId: Type.Optional(Type.String()),
+  label: Type.Optional(
+    Type.String({ minLength: 1, maxLength: SESSION_LABEL_MAX_LENGTH }),
+  ),
+  agentId: Type.Optional(Type.String({ minLength: 1, maxLength: 64 })),
   message: Type.String(),
   timeoutSeconds: Type.Optional(Type.Number({ minimum: 0 })),
 });