Test webhooks
Verify what Stripe, GitHub, Slack and other providers actually send before you write the handler.
Spin up a unique URL, point any client at it, and watch every request stream in: headers, body, query string, timing.
Verify what Stripe, GitHub, Slack and other providers actually send before you write the handler.
Point your HTML form's action
at a unique URL and see exactly what the browser submits.
Inspect outbound calls from third-party services or your own client libraries while you wire them up.
Point a device or microcontroller at the URL to see exactly what it puts on the wire: headers, body, every byte.
Catch your scheduled tasks in the act and confirm they fire on time with the headers and payload you expect.
Anyone with the URL can read the same stream. Handy for "is the payload from your side malformed, or mine?" conversations.