Is this for Slack incoming webhooks?

No. Slack incoming-webhook URLs receive messages sent into Slack. This page covers HTTP requests sent from Slack to your app: Events API callbacks, slash commands, shortcuts, modal submissions, and other interactivity.

Do I need to install CatchHook's Slack App?

No. Incoming Slack request verification belongs to the endpoint and your Slack app's private signing secret. CatchHook's outgoing Slack App is a separate notification, recap, command, and unfurl integration.

Can CatchHook complete Slack Events API URL verification?

Yes. On a permanent endpoint with Slack signature verification enabled, a valid signed url_verification request receives HTTP 200 with its bounded challenge in plaintext. Unverified challenge-shaped bodies are never echoed automatically.

How does CatchHook verify Slack requests?

CatchHook computes Slack's v0 HMAC SHA-256 signature over the exact raw request body and X-Slack-Request-Timestamp using the configured app signing secret. Requests outside Slack's five-minute tolerance fail verification.

Why did Slack retry my event?

Slack retries when it does not receive a successful acknowledgment in time or encounters another delivery error. CatchHook records X-Slack-Retry-Num and X-Slack-Retry-Reason alongside the stable event ID.

Can I replay a Slack event with a valid signature?

Yes, to a controlled destination. Re-sign mode replaces the historical timestamp and signature with fresh values calculated from the exact replay body. Strip mode removes both headers. Preserve mode warns that the captured signature is normally stale.

Does CatchHook reuse trigger IDs or response URLs?

No. trigger_id values expire after three seconds and can be used only once. response_url values are sensitive and time-limited. They remain only in the captured raw request and CatchHook never invokes them automatically.

Does CatchHook expose Slack message text as provider metadata?

No. Promoted metadata is restricted to bounded request classification and stable IDs. Message text, command text, names, private metadata, state, action values, trigger IDs, response URLs, and tokens stay out of provider summaries, comparisons, Actions fields, notifications, REST metadata, and MCP metadata.

No signup required

Slack Events API and Interactivity Webhook Tester

Use CatchHook as the Request URL for a Slack app. Inspect Events API callbacks, retries, slash commands, shortcuts, modal submissions, and block actions without confusing them with Slack incoming-webhook message URLs or CatchHook's outgoing Slack App.

Create Slack Test Endpoint View Slack Request URL Setup

Your Slack Request URL Test Endpoint

Slack events detected automatically

Expires in2 days

The temporary URL can demonstrate Slack event detection. Save it and configure your Slack app signing secret before using automatic Events API URL verification.

Tunnel to localhost

npx @catchhook/tunnel ep_92XYJEnbZAqPFgq0ZVpvey86 --key tkey_0590cf3167a80b867c51cc157ca5a179 --port 3000

Test Your Endpoint

curl -X POST https://temp.catchhook.app/hooks/ep_92XYJEnbZAqPFgq0ZVpvey86 \
  -H "Content-Type: application/json" \
  -d '{
  "type": "event_callback",
  "team_id": "T_TEST_WORKSPACE",
  "api_app_id": "A_TEST_APP",
  "event_id": "Ev_TEST_EVENT",
  "event_time": 1785348000,
  "event": {
    "type": "app_home_opened",
    "user": "U_TEST_USER",
    "channel": "D_TEST_HOME",
    "event_ts": "1785348000.000100"
  }
}'

Or

to see it appear in real time below.

Live Webhook Requests

Watch requests stream in automatically with full headers, payloads, and timestamps.

Streaming Live

Updates automatically

Waiting for your first webhook...

Send a test request using the cURL command above or configure Slack to use your endpoint URL.

How to test Slack webhooks with Catchhook

Follow these steps to start receiving Slack events on your temporary endpoint.

1

Create or open your Slack development app

Use Slack's app settings for the app whose Events API, slash-command, or interactivity requests you want to inspect. CatchHook does not install or host that app.

2

Save a permanent CatchHook endpoint

Slack Request URLs must remain stable. Save the temporary endpoint before registering it with Slack.

Suggested events:

app_home_openedlink_shared

Slack webhook documentation

3

Configure the Slack app signing secret

In the endpoint signature settings, choose Slack and enter the Signing Secret from the app's Basic Information page. Do not use a bot token, client secret, verification token, response URL, or incoming-webhook URL.

4

Register the CatchHook Request URL

Paste the permanent endpoint URL into Event Subscriptions, Interactivity & Shortcuts, or the slash-command Request URL. A correctly signed Events API challenge receives an automatic plaintext challenge response.

5

Trigger and inspect a real request

CatchHook keeps the exact captured request while promoting only bounded workspace, app, event, user, channel, action, view, and retry identifiers for summaries, filters, Actions, comparisons, REST, and MCP.

Slack request families to test

Events API callbacks

Good for

event subscriptions
retry and idempotency handling
App Home and link-unfurl workflows

type: event_callback

Slash commands

Good for

command routing
fast acknowledgments
expired response-context diagnostics

command: /your-command

Block Kit interactions

Good for

button and menu actions
shortcuts
modal submissions

payload.type: block_actions

Events API URL verification

Good for

Request URL registration
signing-secret validation
response evidence

type: url_verification

Common Slack webhook problems this helps debug

Catchhook helps you diagnose these issues before they reach production.

Slack rejects the Request URL

The CatchHook endpoint is permanent and publicly reachable over HTTPS
The endpoint has the correct Slack app Signing Secret enabled
The challenge request contains both Slack signature headers
CatchHook recorded a verified provider_handshake response with HTTP 200

Signature verification fails

Slack signs v0:{timestamp}:{exact raw body}. Form decoding, JSON reformatting, character-encoding changes, a timestamp outside five minutes, or the wrong app signing secret can all make verification fail. CatchHook verifies the original bytes before provider enrichment.

Slack retries the event

Inspect Slack retry and delivery identity together:

X-Slack-Retry-Num identifies the retry attempt
X-Slack-Retry-Reason explains why Slack retried
event_id remains the logical Events API identity
Return HTTP 200 quickly and make side effects idempotent

A replay behaves differently

Captured Slack signatures expire after five minutes. Preserve mode is historical, strip mode removes both Slack signature headers, and re-sign mode generates a fresh timestamp and v0 signature. trigger_id values expire after three seconds and response_url values are sensitive historical context; CatchHook never invokes either automatically.

What you get for free

Free / no signup

temporary unsigned Events API demonstration
live request and header inspection
Slack event-family detection
bounded event and retry context
generated cURL test
localhost tunnel command
short-lived request history

Signup / free trial

permanent Slack Request URL
Slack signing-secret verification and rotation
automatic verified URL challenge responses
fresh replay signature generation
Replay Cases and semantic comparison
Endpoint Actions using privacy-safe Slack fields
alerts and production monitoring
REST and MCP diagnostics

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When to create a permanent endpoint

Save the endpoint before registering it with Slack. Permanent endpoints can verify your private app signing secret, complete URL verification, retain request history, re-sign controlled replays, and power Actions, alerts, Replay Cases, REST, and MCP.

Save This Slack Request URL

Frequently Asked Questions

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