diff --git a/packages/slack/src/message.test.ts b/packages/slack/src/message.test.ts
index 04ad6f6..ab43dfd 100644
--- a/packages/slack/src/message.test.ts
+++ b/packages/slack/src/message.test.ts
@@ -4,101 +4,110 @@ import { formatMessage } from "./message";
 describe("formatMessage", () => {
   describe("markdown to Slack formatting", () => {
     test("converts markdown links to Slack format", () => {
-      expect(formatMessage("[click here](https://example.com)")).toBe(
+      expect(formatMessage("[click here](https://example.com)").text).toBe(
         "<https://example.com|click here>"
       );
     });
 
     test("converts double-star bold to single-star bold", () => {
-      expect(formatMessage("**hello**")).toBe("*hello*");
+      expect(formatMessage("**hello**").text).toBe("*hello*");
     });
   });
 
   describe("user ID mention wrapping", () => {
     test("wraps @-prefixed Slack user IDs", () => {
-      expect(formatMessage("@U02UD2WE3HA")).toBe("<@U02UD2WE3HA>");
+      expect(formatMessage("@U02UD2WE3HA").text).toBe("<@U02UD2WE3HA>");
     });
 
     test("wraps bare Slack user IDs", () => {
-      expect(formatMessage("user U02UD2WE3HA said")).toBe(
+      expect(formatMessage("user U02UD2WE3HA said").text).toBe(
         "user <@U02UD2WE3HA> said"
       );
     });
 
     test("wraps workspace IDs starting with W", () => {
-      expect(formatMessage("@W01AB2CD3EF")).toBe("<@W01AB2CD3EF>");
+      expect(formatMessage("@W01AB2CD3EF").text).toBe("<@W01AB2CD3EF>");
     });
 
     test("does not double-wrap already bracketed IDs", () => {
-      expect(formatMessage("<@U02UD2WE3HA>")).toBe("<@U02UD2WE3HA>");
+      expect(formatMessage("<@U02UD2WE3HA>").text).toBe("<@U02UD2WE3HA>");
     });
 
     test("removes brackets from non-ID @handles", () => {
-      expect(formatMessage("<@john.doe>")).toBe("@john.doe");
+      expect(formatMessage("<@john.doe>").text).toBe("@john.doe");
     });
   });
 
   describe("false-positive prevention", () => {
     test("does not match pure-alpha words like WORKSPACE", () => {
       const input = "CODER_WORKSPACE_IS_PREBUILD_CLAIM=true";
-      expect(formatMessage(input)).toBe(input);
+      expect(formatMessage(input).text).toBe(input);
     });
 
     test("does not match UPPERCASE without digits", () => {
-      expect(formatMessage("UNDEFINED")).toBe("UNDEFINED");
-      expect(formatMessage("WORKSPACEID")).toBe("WORKSPACEID");
+      expect(formatMessage("UNDEFINED").text).toBe("UNDEFINED");
+      expect(formatMessage("WORKSPACEID").text).toBe("WORKSPACEID");
     });
 
     test("does not match short IDs", () => {
-      expect(formatMessage("U1234")).toBe("U1234");
+      expect(formatMessage("U1234").text).toBe("U1234");
     });
   });
 
   describe("code block preservation", () => {
     test("does not format IDs inside inline code", () => {
       const input = "`U02UD2WE3HA`";
-      expect(formatMessage(input)).toBe(input);
+      expect(formatMessage(input).text).toBe(input);
     });
 
     test("does not format IDs inside code blocks", () => {
       const input = "```\nU02UD2WE3HA\n```";
-      expect(formatMessage(input)).toBe(input);
+      expect(formatMessage(input).text).toBe(input);
     });
 
     test("formats IDs outside code but preserves code content", () => {
       const input = "user U02UD2WE3HA said `U02UD2WE3HA`";
-      expect(formatMessage(input)).toBe(
+      expect(formatMessage(input).text).toBe(
         "user <@U02UD2WE3HA> said `U02UD2WE3HA`"
       );
     });
 
     test("preserves markdown links inside code blocks", () => {
       const input = "```\n[text](url)\n```";
-      expect(formatMessage(input)).toBe(input);
+      expect(formatMessage(input).text).toBe(input);
     });
 
     test("preserves bold syntax inside inline code", () => {
       const input = "`**not bold**`";
-      expect(formatMessage(input)).toBe(input);
+      expect(formatMessage(input).text).toBe(input);
     });
 
     test("handles multiple code blocks", () => {
       const input = "`U02UD2WE3HA` and U02UD2WE3HA and ```U02UD2WE3HA```";
-      expect(formatMessage(input)).toBe(
+      expect(formatMessage(input).text).toBe(
         "`U02UD2WE3HA` and <@U02UD2WE3HA> and ```U02UD2WE3HA```"
       );
     });
 
     test("does not format IDs inside code blocks with more than 3 backticks", () => {
       const input = "````\nU02UD2WE3HA\n````";
-      expect(formatMessage(input)).toBe(input);
+      expect(formatMessage(input).text).toBe(input);
     });
   });
 
   describe("truncation", () => {
     test("truncates text longer than 3000 characters", () => {
       const input = "a".repeat(4000);
-      expect(formatMessage(input).length).toBe(3000);
+      const result = formatMessage(input);
+      expect(result.text.length).toBe(3000);
+      expect(result.truncated).toBe(true);
+      expect(result.originalLength).toBe(4000);
+    });
+
+    test("does not mark short messages as truncated", () => {
+      const result = formatMessage("hello");
+      expect(result.truncated).toBe(false);
+      expect(result.originalLength).toBe(5);
     });
   });
 });
diff --git a/packages/slack/src/message.ts b/packages/slack/src/message.ts
index cce864f..ad4fa26 100644
--- a/packages/slack/src/message.ts
+++ b/packages/slack/src/message.ts
@@ -24,9 +24,15 @@ import type { KnownEventFromType } from "@slack/bolt";
  * @param text - The text to format.
  * @returns The formatted text.
  */
-export function formatMessage(text: string): string {
+export function formatMessage(text: string): {
+  text: string;
+  truncated: boolean;
+  originalLength: number;
+} {
   const maxLength = 3000;
-  if (text.length > maxLength) {
+  const originalLength = text.length;
+  const truncated = text.length > maxLength;
+  if (truncated) {
     text = text.slice(0, maxLength);
   }
 
@@ -71,7 +77,7 @@ export function formatMessage(text: string): string {
     text = text.replace(placeholder(i), preserved[i] ?? "");
   }
 
-  return text;
+  return { text, truncated, originalLength };
 }
 
 /**
@@ -86,6 +92,7 @@ export const formattingRules = `FORMATTING RULES:
 - <http://example.com|link text> = links
 - tables must be in a code block
 - user mentions must be in the format <@user_id> (e.g. <@U01UBAM2C4D>)
+- messages are limited to 3000 characters; if your response is longer, it will be truncated and you'll need to send follow-up messages
 
 NEVER USE:
 - Headings (#, ##, ###, etc.)
diff --git a/packages/slack/src/tools.ts b/packages/slack/src/tools.ts
index 28f6e43..e50b1a2 100644
--- a/packages/slack/src/tools.ts
+++ b/packages/slack/src/tools.ts
@@ -113,7 +113,7 @@ ${formattingRules}`
           throw new Error("ts is required! Messaging in channels is disabled.");
         }
 
-        const text = formatMessage(args.message);
+        const { text, truncated, originalLength } = formatMessage(args.message);
         const blocks: AnyBlock[] = [
           {
             type: "section",
@@ -158,6 +158,13 @@ ${formattingRules}`
         if (!res.ok) {
           throw new Error(`Failed to send message: ${res.error}`);
         }
+        if (truncated) {
+          return {
+            success: true,
+            truncated: true,
+            message: `Your message was truncated from ${originalLength} to 3000 characters due to Slack's message limit. The last 100 characters sent were: "${text.slice(-100)}". Send a follow-up message to continue where you left off.`,
+          };
+        }
         return {
           success: true,
         };