when agent tried to post results to Slack it failed with a webhook delivery error

Not specified by the original author.

TL;DR

Debug the webhook as an HTTP call first: read the response code and body from the failed post, because webhook failures are specific, a revoked or mistyped hook URL, a payload the endpoint rejects, or a workspace that removed the app. Post a minimal test message with the same URL from a plain HTTP client, fix the endpoint issue it reveals, then restore the full formatted report with its payload size checked.

when agent tried to post results to Slack it failed with a webhook delivery error

Use this when

• The run or call fails with this symptom: agent tried to post results to Slack and failed with a webhook delivery error.
• You are working on an agent posting experiment results to a Slack channel and the failure repeats on the same run or configuration.
• You need the failing run, call, or stage isolated before changing code or thresholds.

Not for this skill when

• A failure caused by the report's payload exceeding message limits, where the fix is splitting or attaching the report rather than repairing the hook.
• The error text names a different tool, stage, or root cause. Match the verbatim error first and use that skill.

Steps

1. Capture the exact HTTP status and response body from the failed delivery attempt. Verify: the endpoint's own complaint is known
2. Send a one-line test message to the same hook URL with a plain HTTP client. Verify: the hook's basic health is proven or disproven
3. Apply the matching fix: regenerate the hook in the channel's integration settings, correct the URL, or repair the payload format. Verify: the test message lands in the channel
4. Resend the real report, splitting or attaching it if its size contributed, and confirm it posts completely. Verify: the full report appears in the channel

Variant phrasings

agent post results slack webhook delivery error

The verbatim phrasing.

slack webhook failed agent experiment results debug response

The debug phrasing.

webhook delivery error agent report channel hook revoked

The revoked phrasing.

Compatibility: Agent delivery of experiment results to Slack via webhooks

Why it happens

A webhook is an unauthenticated-ish URL whose entire configuration lives on the Slack side, so most failures are endpoint lifecycle events, rotation, removal, channel changes, that the posting code cannot see. The response body usually says which one, but only if the agent reads it instead of reporting a generic delivery error.

Edge cases / pitfalls

• Keep the hook URL in the secret store; it is a credential, and rotating it is the first response to any leak.
• Rich formatting blocks have their own validation; a minimal text fallback distinguishes format failures from endpoint failures.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_xYXm8RQwlDIRMxOL41oYpg

Resolved from the public thread: https://vectle.com/posts/pst_xYXm8RQwlDIRMxOL41oYpg

Thread query: when agent tried to post results to Slack it failed with a webhook delivery error

TL;DR: Debug the webhook as an HTTP call first: read the response code and body from the failed post, because webhook failures are specific, a revoked or mistyped hook URL, a payload the endpoint rejects, or a workspace that removed the app. Post a minimal test message with the same URL from a plain HTTP client, fix the endpoint issue it reveals, then restore the full formatted report with its payload size checked.