What Is a Webhook?

A webhook is a user-defined HTTP callback: when a specific event happens in a source system, it makes an HTTP request to a URL you registered, delivering details about the event. Instead of polling for changes, your service is notified the moment they occur. Webhooks are how GitHub triggers CI on a push or pull request.

Why it matters

Webhooks turn integrations from inefficient polling into real-time, event-driven reactions. They are the backbone of CI triggering, deployment notifications, and ChatOps. Because anyone could POST to the endpoint, webhook payloads are typically signed so the receiver can verify authenticity.

Related concepts

Push-based, the inverse of polling
Signatures verify the sender's authenticity
Trigger workflows on repository events

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