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Slack Trigger

The Slack Trigger node is a zero-input entry point that receives Slack Events API webhooks and starts a workflow automatically.

The Slack Trigger node is a zero-input entry point that receives Slack Events API webhooks and starts a workflow automatically. It handles Slack's URL verification challenge and verifies request signatures with a signing secret.

Overview

PropertyValue
Inputs0
Outputs1
Output$nodeLabel.event, $nodeLabel.headers, $nodeLabel.triggered_by, $nodeLabel.trigger_node_id

Parameters

ParameterTypeDescription
credentialIdUUIDslack_trigger credential containing the signing secret

Setup Guide

1. Create a slack_trigger Credential

  1. Go to Settings → Credentials → New Credential
  2. Select type Slack Trigger (Signing Secret)
  3. Paste the Signing Secret from your Slack App:
    • In Slack: App settings → Basic Information → App Credentials → Signing Secret
  4. Save the credential

2. Add the Node to Your Workflow

  1. Open the workflow canvas
  2. Drag Slack Trigger from the node panel onto the canvas
  3. Click the node to open the Properties panel
  4. Select your slack_trigger credential
  5. Copy the Webhook URL shown in the panel

3. Configure Your Slack App

  1. In your Slack App settings go to Event Subscriptions
  2. Toggle Enable Events on
  3. Paste the Webhook URL into the Request URL field
  4. Slack sends a URL verification challenge — Heym responds automatically within milliseconds
  5. The field turns green: ✓ Verified
  6. Subscribe to the Bot Events you need (e.g. message.channels, reaction_added)
  7. Save your changes and reinstall the app to your workspace if prompted

Output Fields

After the node triggers, downstream nodes can access:

ExpressionDescription
$nodeLabel.eventFull Slack event object
$nodeLabel.event.typeEvent type (e.g. "message", "reaction_added")
$nodeLabel.event.textMessage text (when applicable)
$nodeLabel.event.userSlack user ID who triggered the event
$nodeLabel.event.channelChannel ID
$nodeLabel.event.tsEvent timestamp
$nodeLabel.headersSanitized HTTP headers from Slack
$nodeLabel.triggered_byTrigger source label ("Slack")
$nodeLabel.trigger_node_idCanvas node ID that received the Slack event

Example Workflow

Slack message → LLM reply → Slack send:

slackTrigger → llm → slack
  • slackTrigger label: slackEvent
  • LLM user message: "Reply to this Slack message: $slackEvent.event.text"
  • Slack message: $llm.text

Security

  • Requests are verified using HMAC-SHA256 with your signing secret
  • Timestamps older than 5 minutes are rejected (replay attack prevention)
  • Sensitive headers (x-slack-signature, authorization, etc.) are stripped before they reach downstream nodes
  • If no credential is set the node runs without verification — only recommended for local testing

Notes

  • Heym responds with 200 OK immediately and runs the workflow in the background — this satisfies Slack's 3-second response requirement
  • The webhook URL is derived from the node ID and never changes, even after workflow renames
  • Only one slackTrigger node per workflow is needed; use Switch or Condition nodes downstream to route different event types