Webhook

A webhook is a way for one system to notify another the instant something happens, by sending an HTTP request, usually a POST with a JSON payload, to a URL the receiving system has registered in advance. When a payment succeeds, a form is submitted, or a deployment finishes, the source system fires the webhook automatically, with no polling required.

This push model is the opposite of a typical API integration, where the receiving system has to repeatedly call the source's API and ask whether anything new happened. Webhooks are more efficient and lower-latency for event notification, but they also require the receiver to expose a reachable, reliable endpoint that can accept requests at any time, handle retries from the sender, and avoid processing the same event twice if it's delivered more than once.

Webhooks are a common building block of event-driven architecture and a frequent source of data ingestion for pipelines that need to react to third-party events, a new subscription, a support ticket, a shipment update, in near real time. The main pitfalls are not verifying that an incoming webhook actually came from the expected sender, not handling duplicate deliveries, since most providers guarantee at-least-once delivery rather than exactly-once, and having no fallback if the receiving endpoint is briefly down and events are missed.