Webhook

A webhook inverts the usual request-response flow. Instead of your application repeatedly asking an API whether something has happened (polling), you register a URL with the provider; when the relevant event occurs, the provider sends an HTTP request - typically a POST carrying a JSON payload - to that URL. Webhooks are therefore often described as event-driven, reverse, or push APIs.

Because webhooks deliver updates the moment an event fires, they are efficient for things like completed jobs, payments, or status changes, where polling would waste requests and add latency. The receiver exposes an endpoint that accepts the request, acknowledges it quickly, and processes the payload.

Securing and reliably handling webhooks requires care. Receivers should verify that an incoming request genuinely came from the provider - commonly by checking a cryptographic signature included in the request headers - and must tolerate retries, since providers re-send deliveries that are not acknowledged. That re-delivery is also why webhook handlers are typically made idempotent, so processing the same event twice has no harmful effect.