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An event-triggered HTTP request sent by one system to a registered endpoint in another system to notify it that something has happened.

Webhooks reduce latency and unnecessary API requests in connected workflows. They are commonly used to trigger fulfillment, synchronize records, start automation, and notify downstream services.

A payment platform sends a signed webhook after a successful payment. The receiving service verifies the signature, checks the event ID for duplicates, updates the order, and queues fulfillment.

Webhook delivery is generally not equivalent to exactly-once processing. Requests can be duplicated, delayed, reordered, or lost after retry limits. Public endpoints also create an attack surface and must not trust payloads without verification.

The producer sends a payload—commonly JSON—to a subscriber endpoint when a defined event occurs. Production implementations require event identifiers, authentication or signatures, timeouts, retries, idempotent processing, ordering assumptions, observability, and a strategy for dead-letter or failed deliveries. Webhooks enable push-based integration rather than repeated polling.