Slack Trigger

Overview

Start a workflow when something happens in Slack. The trigger has two delivery modes:

• Real-time events (recommended) — Slack pushes events to Falcon Builder via the Events API. Supports messages, mentions, reactions, file shares, new channels, and new users.
• Polling — Falcon Builder checks a channel every few minutes for new messages. No event-subscription setup, but new-messages only and slightly delayed.

Supported Events (real-time mode)

• New message in channel — message (scope channels:history)
• App / bot mentioned — app_mention (scope app_mentions:read)
• Reaction added — reaction_added (scope reactions:read)
• File shared — file_shared (scope files:read)
• New channel created — channel_created (scope channels:read)
• New user joined workspace — team_join (scope users:read)

Setup (real-time)

• Step 1: Add the Signing Secret to your Slack credential (from your Slack app's Basic Information page).
• Step 2: In your Slack app under Event Subscriptions, set the Request URL to https://www.falconbuilder.dev/api/webhooks/slack/events. Slack sends a verification challenge that we answer automatically.
• Step 3: Subscribe to the bot events you need (e.g. message.channels, app_mention, reaction_added), add the matching scopes, and reinstall the app.
• Step 4: In the trigger node, pick Real-time events, select the events, and optionally scope to one channel.

The fastest path is the ready-made app manifest on the Slack credential page — it pre-declares all scopes, event subscriptions, and the Request URL in one paste.

Trigger output ($json)

• {{$json.event}} — the event type (e.g. app_mention)
• {{$json.channel}} — the channel ID
• {{$json.user}} — the Slack user ID who triggered it
• {{$json.slackEvent.text}} — message text (for message / mention events)
• {{$json.slackEvent.ts}} — the event timestamp (use it to reply in-thread)

Common Use Cases

• Slack-native assistant — answer when the bot is @mentioned in any channel
• Reaction workflows — kick off a task when someone adds a specific emoji
• Onboarding — DM a checklist when a new user joins the workspace
• File intake — process documents shared into a channel

Notes

• Real-time events require the Signing Secret on the credential — we reject unsigned or mis-signed requests.
• For message and app_mention events, the Text Contains and Ignore Bots filters apply (same as polling). Message edits, deletes, and joins are skipped, and the app's own messages never re-trigger it.
• Polling mode is new-messages only and runs on a few-minute schedule; use real-time for anything else.

Required Credentials