Teams App Developer

bolt-assistant-ts

purpose

Slack Assistant container patterns for Bolt.js — Assistant class configuration, thread lifecycle handlers (threadStarted, userMessage, threadContextChanged), utility functions (say, setStatus, setSuggestedPrompts, setTitle), and thread context storage.

rules

1. Provide threadStarted and userMessage handlers (required). These are the minimum callbacks for an Assistant. threadContextChanged is optional and defaults to saving context via the thread context store. slack.dev/bolt-js/concepts/assistant

2. Call setStatus() to show typing indicators. Use await setStatus("Thinking...") at the start of userMessage to show the user that processing is happening. The status clears automatically when the bot sends a reply via say(), or pass an empty string to clear manually. api.slack.com/docs/assistants

3. Use setSuggestedPrompts() in threadStarted. Provide up to 4 preset prompts with title and message properties. This helps users discover what the assistant can do. An optional top-level title parameter labels the prompt group (defaults to "Try these prompts:"). api.slack.com/docs/assistants

4. Use setTitle() to label conversation threads. Call setTitle(summary) after processing the first userMessage to give the thread a meaningful name in the sidebar. api.slack.com/docs/assistants

5. Thread context is NOT included in userMessage events. The message event payload does not carry thread context. Call await getThreadContext() in userMessage handlers to retrieve the current context (channel_id, team_id, enterprise_id). slack.dev/bolt-js/concepts/assistant

6. Use saveThreadContext() in threadStarted. The initial thread context (which channel the user was viewing) arrives in the threadStarted event. Save it immediately so userMessage handlers can retrieve it later. slack.dev/bolt-js/concepts/assistant

7. The default AssistantThreadContextStore uses message metadata. Context is persisted by updating the bot's first message in the thread with metadata. This survives app restarts without external storage. For production, implement a custom store backed by a database. slack.dev/bolt-js/concepts/assistant

8. Register the assistant with app.assistant(assistant). This adds middleware that intercepts assistant_thread_started, assistant_thread_context_changed, and thread messages. The middleware stops propagation — registered app.message() handlers will NOT fire for assistant threads. slack.dev/bolt-js/concepts/assistant

9. threadContextChanged fires when the user switches channels. The updated context is in event.assistant_thread.context. The default behavior (when handler is omitted) automatically calls saveThreadContext() to persist the new context.

10. All handlers receive the same utility set. Every handler gets: say, getThreadContext, saveThreadContext, setStatus, setSuggestedPrompts, setTitle, plus the standard client, context, and logger.

patterns

Basic assistant with suggested prompts and status

import { App, Assistant } from "@slack/bolt";

const app = new App({
  token: process.env.SLACK_BOT_TOKEN!,
  appToken: process.env.SLACK_APP_TOKEN!,
  socketMode: true,
});

const assistant = new Assistant({
  threadStarted: async ({ say, setSuggestedPrompts, saveThreadContext }) => {
    await saveThreadContext();
    await say("Hi! How can I help?");
    await setSuggestedPrompts({
      title: "Try one of these:",
      prompts: [
        { title: "Summarize", message: "Summarize this channel's recent messages" },
        { title: "Draft", message: "Help me draft a message" },
        { title: "Search", message: "Search our docs for..." },
      ],
    });
  },

  userMessage: async ({ message, say, setStatus, setTitle, getThreadContext }) => {
    await setStatus("Thinking...");

    const context = await getThreadContext();
    const channelId = context?.channel_id;
    const userText = message.text ?? "";

    // Set thread title from first message
    await setTitle(userText.slice(0, 50));

    // Business logic / AI call here...
    const answer = await generateAnswer(userText, channelId);
    await say(answer);
  },
});

app.assistant(assistant);

async function generateAnswer(text: string, channelId?: string): Promise<string> {
  return `You asked: "${text}" (from channel ${channelId ?? "unknown"})`;
}

(async () => {
  await app.start();
  console.log("Assistant is running");
})();

Custom thread context store backed by a database

import { type AssistantThreadContextStore, type AllAssistantMiddlewareArgs, type AssistantThreadContext } from "@slack/bolt";

const contextStore: AssistantThreadContextStore = {
  async get({ payload }: AllAssistantMiddlewareArgs): Promise<AssistantThreadContext> {
    const threadTs = "assistant_thread" in payload
      ? payload.assistant_thread.thread_ts
      : payload.thread_ts;
    const row = await db.query("SELECT context FROM assistant_threads WHERE thread_ts = $1", [threadTs]);
    return row?.context ?? {};
  },

  async save({ payload }: AllAssistantMiddlewareArgs): Promise<void> {
    const threadTs = "assistant_thread" in payload
      ? payload.assistant_thread.thread_ts
      : payload.thread_ts;
    const context = "assistant_thread" in payload
      ? payload.assistant_thread.context
      : {};
    await db.query(
      "INSERT INTO assistant_threads (thread_ts, context) VALUES ($1, $2) ON CONFLICT (thread_ts) DO UPDATE SET context = $2",
      [threadTs, context]
    );
  },
};

const assistant = new Assistant({
  threadContextStore: contextStore,
  threadStarted: async ({ saveThreadContext, say }) => {
    await saveThreadContext(); // uses custom store
    await say("Hello! I'm ready to help.");
  },
  userMessage: async ({ getThreadContext, say, setStatus }) => {
    await setStatus("Processing...");
    const ctx = await getThreadContext(); // reads from custom store
    await say(`Context channel: ${ctx?.channel_id}`);
  },
});

Handling context changes with custom logic

const assistant = new Assistant({
  threadStarted: async ({ saveThreadContext, say, setSuggestedPrompts }) => {
    await saveThreadContext();
    await say("I'll adapt to whatever channel you're viewing.");
    await setSuggestedPrompts({
      prompts: [
        { title: "What's happening?", message: "What's the latest in this channel?" },
      ],
    });
  },

  userMessage: async ({ getThreadContext, say, setStatus }) => {
    await setStatus("Looking up context...");
    const ctx = await getThreadContext();
    await say(`You're currently viewing <#${ctx?.channel_id ?? "unknown"}>.`);
  },

  threadContextChanged: async ({ event, saveThreadContext, logger }) => {
    const newChannel = event.assistant_thread.context?.channel_id;
    logger.info(`User switched to channel: ${newChannel}`);
    await saveThreadContext(); // persist the new context
  },
});

pitfalls

• Forgetting saveThreadContext() in threadStarted: Without saving, getThreadContext() in userMessage returns empty/stale data. The initial context is only available in the threadStarted event.

• Assistant middleware blocks app.message() handlers: Once app.assistant() is registered, messages in assistant threads are consumed by the Assistant middleware and do NOT propagate to app.message() listeners. Don't register duplicate handlers.

• setSuggestedPrompts limit of 4: Passing more than 4 prompts causes the API to reject the call. Keep it to 4 or fewer.

• Default context store requires bot to post first: The DefaultThreadContextStore saves context as metadata on the bot's first message. If threadStarted doesn't call say(), there's no message to attach metadata to, and context storage fails silently.

• No ack() in assistant handlers: Unlike actions/commands, assistant handlers don't have an ack() function. Events are fire-and-forget from Slack's perspective.

• message.text can be undefined: Always handle the case where message.text is undefined (e.g., when the user sends only an attachment).

references

• https://api.slack.com/docs/assistants

• https://slack.dev/bolt-js/concepts/assistant

• https://github.com/slackapi/bolt-js/blob/main/src/Assistant.ts

• https://github.com/slackapi/bolt-js/blob/main/src/AssistantThreadContextStore.ts

instructions

This expert covers the Slack Assistant container for Bolt.js in TypeScript. Use it when you need to: create an AI assistant that lives in Slack's assistant panel; handle thread lifecycle events (threadStarted, userMessage, threadContextChanged); use utility functions for status indicators, suggested prompts, and thread titles; implement custom thread context stores for production persistence; and understand the middleware behavior that separates assistant threads from regular message handlers. Pair with runtime.bolt-foundations-ts.md for general Bolt app setup and ui.block-kit-ts.md for rich message formatting within assistant responses.

research

Deep Research prompt:

"Write a micro expert on the Slack Assistant container in Bolt.js TypeScript. Cover: Assistant class constructor (threadStarted, userMessage, threadContextChanged, threadContextStore), utility functions (say, setStatus, setSuggestedPrompts, setTitle, getThreadContext, saveThreadContext), AssistantThreadContextStore interface (get, save), DefaultThreadContextStore message metadata pattern, app.assistant() registration and middleware behavior, thread lifecycle event payloads, and common patterns for AI-powered assistants. Provide 2-3 canonical TypeScript examples."