Slack Webhook Tester — Test & Inspect Slack Webhooks Online

If you are wiring up Slack webhooks, the first question is always the same: what does Slack actually send? The docs show an idealised payload, but the real request — its headers, its X-Slack-Signature header, the exact JSON shape — is what your handler has to parse. A Slack webhook tester gives you a public URL that captures those real requests so you can read every byte before you write any code.

Get a free Slack webhook tester URL

The fastest way is our free Webhook Bin — a no-code webhook tester that gives you an instant public URL and stores every request that hits it, headers and body included. No signup, no deploy:

1. Open the Webhook Bin and copy the URL it generates for you.
2. In api.slack.com/apps → your app → Event Subscriptions, add a webhook endpoint and paste that URL.
3. Trigger an event (see below) and watch the request land in the bin in real time.

Because the bin keeps the full request, you can inspect the X-Slack-Signature header, the Content-Type, and the complete payload — the three things you need to build and verify a handler.

What a Slack webhook looks like

Slack delivers webhooks as an HTTP POST with a application/json body. Before any events arrive, Slack sends a one-time url_verification challenge that your endpoint must echo back. Capturing it in a bin lets you see the exact challenge value Slack expects — a common first-time stumbling block.

A typical app_mention payload looks like this:

{
  "type": "event_callback",
  "team_id": "T...",
  "event": {
    "type": "app_mention",
    "user": "U...",
    "text": "<@U...> hello",
    "channel": "C..."
  }
}

Common Slack events you will want to test:

• app_mention
• message.channels
• reaction_added
• url_verification

Verifying the Slack signature

Slack signs each request so you can prove it really came from Slack. The signature travels in the X-Slack-Signature header and is v0= HMAC-SHA256 over v0:timestamp:body, paired with the X-Slack-Request-Timestamp header, using your app's Signing Secret. Capture a real request first, then use our HMAC signature verifier and the verify a webhook signature guide to confirm your verification logic against a payload you can actually see.

From inspecting to receiving on localhost

A bin is perfect for seeing the payload. When you are ready to drive your local handler with real Slack events — without deploying — forward them straight to localhost with the Webhook Relay agent. The full walkthrough is here: Receive Slack webhooks on localhost.

That gives you a stable public URL that tunnels to your machine, so Slack keeps delivering to the same endpoint while you iterate on localhost, no firewall changes or public IP required.

Test Slack webhooks online in three steps

1. Capture — point Slack at a Webhook Bin URL and inspect the real request.
2. Verify — confirm the X-Slack-Signature header with the HMAC verifier.
3. Forward — when the shape is clear, receive Slack webhooks on localhost and build your handler.

New to webhooks in general? Start with what is a webhook and how to test webhooks.

Ready to inspect your first Slack event? Open a free Webhook Bin and paste the URL into Slack.