Setup tips & tricks — Slack × CMA webhook bridge

Slack mentions trigger a Claude Managed Agent session by configuring a webhook bridge that captures Slack @mention events and routes the final CMA reply back into the originating Slack thread using stateless routing metadata.

Duplicate replies in a Slack to Managed Agent webhook bridge happen when event handling lacks idempotency. Deduplicate incoming triggers using Slack event_id and Anthropic event.id keys to prevent processing the same request multiple times.

The Anthropic CMA webhook acts as a doorbell signal rather than delivering the payload directly. Upon receiving the session-idle signal, make follow-up API calls to retrieve metadata and fetch final outcomes to post back to Slack.

Debugging Slack event subscription and CMA webhook verification failures involves checking for token mix-ups, verifying correct webhook workspace scoping, and validating webhook signature verification for both Slack events and Anthropic session-idle signals.

You do not need a stateful server to route Anthropic Managed Agent replies to Slack threads. The bridge uses stateless routing metadata extracted from the initial mention to map the CMA session back to the correct Slack thread.