AI Agents · Lesson

Listening to Events and Slash Commands

app_mention, slash commands, and action handlers in Slack Bolt.

Slack Event Subscriptions Overview

Slack sends your app events when things happen — a message posted, someone mentioning your bot, a user joining a channel. You subscribe to specific event types in the Slack App dashboard, then register handlers in Bolt using the @app.event() decorator.

from slack_bolt import App
import os

app = App(
    token=os.environ['SLACK_BOT_TOKEN'],
    signing_secret=os.environ['SLACK_SIGNING_SECRET']
)

# Register event handlers with @app.event()
# The string argument must match the Slack event type exactly

@app.event('app_mention')
def handle_mention(event, say, logger):
    logger.info(f'Mention event: {event}')
    say(f'Hello <@{event["user"]}>!')

@app.event('message')
def handle_message(event, say):
    # Fires for every message in subscribed channels
    if event.get('subtype') is None:  # ignore bot messages
        print(f'Message: {event["text"]}')

Handling app_mention Events

The app_mention event fires when someone types @YourBot in a channel. The event['text'] contains the full message including the mention. Strip the mention prefix to get the user's actual query.

import re

@app.event('app_mention')
def handle_mention(event, say, client):
    # event['text'] example: '<@U0123BOT> summarize this'
    text = event.get('text', '')
    user_id = event['user']
    channel = event['channel']

    # Remove the @mention to get the clean query
    clean_text = re.sub(r'<@[A-Z0-9]+>', '', text).strip()
    print(f'User {user_id} asked: {clean_text}')

    if not clean_text:
        say(f'Hi <@{user_id}>! How can I help you today?')
        return

    # Process the query
    response = process_user_query(clean_text, user_id)
    say(response)

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