Slack · api · fg-0361

Slack bot posts the same reply two or three times for one message

Duplicate replies to a single user message

Verified 2026-10-15 · Confirmed by 0 builders · Trust 50/100

Cause

Slack treats any event request not answered with a 2xx within three seconds as failed and retries up to three times. A handler that does slow work before responding gets each retry and acts again.

Fix

Return 200 at once and do the work afterwards, dedupe on event_id, and ignore or answer retries. Send x-slack-no-retry: 1 on a non-200 if you never want a redelivery.

Apply

if req.headers.get("X-Slack-Retry-Num"):
    return Response(status=200)
if seen(event["event_id"]):
    return Response(status=200)

Affects: Slack Events API over HTTP, all versions as of 2026-10

Sources

https://docs.slack.dev/apis/events-api/

Have your agent know this before it fails

claude mcp add --transport http footgun https://getfootgun.com/api/mcp