Slack webhook source guide

Set up the webhook in Slack

1. In the Slack app, open Event Subscriptions and set the Request URL to the endpoint's ingestion URL.
2. Slack verifies the URL immediately; Hooks answers the challenge, so the app shows Verified.
3. Subscribe to bot events: app_mention, and message.channels only if you want every channel message.
4. Copy the app's Signing Secret into the Hooks endpoint secret.

Signature verification

• url_verification is answered with {"challenge": "..."} after verification, before storage.
• event_time becomes occurredAt; the channel id becomes project.
• Bot messages (bot_id or subtype = bot_message) are stored but never delivered, which stops loops.

Events Hooks normalizes

Normalized payload

Every adapter produces this shape before filters or templates run. The raw payload and sanitized headers stay attached for audit, but filters and templates read the normalized fields.

{
  "id": "evt_01j9m7c4d5",
  "source": "slack",
  "type": "app_mention.received",
  "action": "received",
  "deliveryId": "Ev01ABCDEF",
  "occurredAt": "2026-11-01T09:14:03.000Z",
  "actor": { "login": "U024BE7LH", "id": "U024BE7LH", "type": "user" },
  "project": "C0123456789",
  "subject": {
    "kind": "message",
    "id": "1719919443.123456",
    "title": "@agent triage the failing deploy",
    "body": "<@U0LAN0Z89> triage the failing deploy",
    "url": "https://acme.slack.com/archives/C0123456789/p1719919443123456"
  }
}

Filter and template examples

{
  "allow": [{ "field": "event.type", "op": "equals", "value": "app_mention.received" }],
  "ignoreBots": true
}

{
  "routineUrl": "https://grok.example.com/routines/abc123",
  "key": "{{secret.GROKBOT_KEY}}",
  "task": "Slack mention from {{event.actor.login}}:\n{{event.subject.body | truncate:2000}}"
}

Retries and the delivery log

408, 425, 429, and 5xx responses retry with backoff and honor Retry-After; other 4xx responses fail permanently with a named code. Every attempt keeps the rendered request and the target response, so a failure points at one field or one status instead of a guess.

Common errors

Pair with a target

Reference

• Receiving eventshttps://hooks.events/docs/receive-events.md
• Verify signatureshttps://hooks.events/docs/signatures.md
• Payload templateshttps://hooks.events/docs/templates.md

Other sources