Receive a Slack Event in Jinba Flow

Use INPUT_SLACK_EVENT when a Slack App sends an event to a flow. Set the Slack Event Subscriptions Request URL to https://<your-flow-host>/api/v2/external/flows/<flow-id>/slack-run; get the host and flow ID from the flow’s Triggers panel. This is the Slack event endpoint, not the generic published API URL. The route answers Slack’s URL verification challenge and passes the inner event object to INPUT_SLACK_EVENT. See Slack credentials for app setup. The route verifies every event with the Slack App’s Signing Secret. Set the step’s signing_secret config to a secret of type SLACK_SIGNING_SECRET (copied from the app’s Basic Information → App Credentials) and publish the flow; the published version is what runs. A flow whose published INPUT_SLACK_EVENT step has no usable signing secret, or a request whose X-Slack-Signature / X-Slack-Request-Timestamp headers are missing, invalid, or older than 5 minutes, is refused with 401 before anything runs. A flow with no published INPUT_SLACK_EVENT step answers 404. Only the url_verification handshake and Slack retries (requests with X-Slack-Retry-Num, which are acknowledged without processing) are answered without a signature.

Accept the event as a flow input

value is an optional JSON string supplied at execution time. use_as_input defaults to true, making the event an API or MCP input. optional defaults to false; set it to true only if the flow can proceed without an event. description is optional.

- id: slack_event
  tool: INPUT_SLACK_EVENT
  config:
    - name: signing_secret
      value: "{{secrets.SLACK_SIGNING_SECRET}}"
  input:
    - name: value
      value: '{"type":"app_mention","text":"Help","channel":"C123"}'

For a local check, the example returns an object with result.type equal to app_mention. Slack sends an event envelope to the endpoint, and Jinba Flow passes the inner event object to the tool. The exact fields depend on the Slack event type, so inspect the actual result before referencing fields downstream.

Reply in the event channel

The original guide showed a Slack mention triggering a reply. After inspecting the event shape, use its channel field with SLACK_POST_MESSAGE:

- id: reply_to_mention
  tool: SLACK_POST_MESSAGE
  needs: [slack_event]
  config:
    - name: token
      value: "{{secrets.SLACK_BOT_TOKEN}}"
  input:
    - name: channel
      value: "{{steps.slack_event.result.channel}}"
    - name: text
      value: "Thanks for mentioning me."

This example expects an event with a channel field and a Slack token that can post there.

Fix a missing or invalid event

If optional is false and no value is supplied, the step fails with “Slack event value is required.” Invalid JSON returns an InputSlackEventTool error and a null result. Check the /slack-run event subscription URL and the JSON payload before changing downstream expressions.

​Accept the event as a flow input

​Reply in the event channel

​Fix a missing or invalid event

Accept the event as a flow input

Reply in the event channel

Fix a missing or invalid event