webhook

A webhook is a technique used by an application to provide real-time information to other applications. It relies on HTTP callbacks that are triggered by qualifying events. When such an event occurs, the source system sends an HTTP POST request to a user-specified URL, with a payload describing the event, typically encoded as JSON.

Setup and operation: To use a webhook, the receiver exposes a public HTTP endpoint and provides the sender with the URL, plus optional security credentials such as a shared secret. When the event occurs, the sender delivers a single request to the URL. The receiver processes the payload and responds with a success status. If delivery fails, many providers retry according to a backoff policy.

Common uses: Webhooks are widely used to connect SaaS services, automation tools, and custom applications. Examples include source control platforms notifying continuous integration services when code is pushed, payment processors signaling completed transactions, and collaboration platforms delivering messages or triggering workflows.

Security and reliability: Important considerations include using HTTPS, validating signatures or tokens to verify a sender, and ensuring payloads are authenticated. Webhooks are usually best-effort and may be delivered out of order or multiple times; idempotent handlers and replay-safe processing are advised. Versioning and event filtering help manage changes.

Relation to APIs and polling: Webhooks differ from polling, where a receiver repeatedly queries a service for updates. Webhooks reduce latency and traffic by pushing events, but require management of endpoint availability and security. They are commonly combined with explicit test events or sandboxes to aid development.