Webhook Handler
Pronunciation: WEB-hook HAND-ler
Also known as: Webhook Endpoint Handler, Callback Handler
Definition
A webhook handler is the server endpoint and processing logic that receives event notifications from a provider and converts trustworthy notifications into application updates.
Overview
What it means
A webhook handler is the server endpoint and processing logic that receives event notifications from a provider and converts trustworthy notifications into application updates. Its main job is to accept events safely, not to assume every message is a new payment.
How it works
A robust handler reads the raw request body, verifies the provider’s required signature and timestamp, validates the event schema, deduplicates the event and stores it durably. It acknowledges promptly and delegates slow work to a background queue. Business transitions are guarded by invoice state and fresh provider evidence where necessary.
Understanding the technical details
Treat receipt and processing as two separate reliability steps. Authenticate the raw request, store its unique event ID and payload digest in durable storage, acknowledge within the provider’s timeout, then dispatch internal work. For each order, use a guarded state transition that tolerates duplicate and out-of-order events. If the processing queue is unavailable, do not silently return success before securing the message. A replay tool should be able to reconstruct missed changes without shipping twice.
Additional protocol context
Handlers face duplicated, delayed, reordered, forged, malformed, and versioned events. A crash after an external side effect but before recording completion can repeat the action. Long synchronous work also increases provider retries and queue pressure.
Handlers should preserve raw bytes, verify freshness, deduplicate atomically, persist before acknowledgment, and move slow work to durable queues. Business actions need idempotency and legal transitions. Structured logs, dead-letter ownership, replay, and reconciliation complete the design. Handler versions should remain traceable.
Common failures and limitations
Network retries, out-of-order events and invalid signatures are normal design concerns. Returning HTTP 200 before a durable event is stored can lose data; performing slow fulfillment synchronously may trigger more retries. Log enough context without exposing API secrets.
Related concepts
Webhook, Webhook Verification, Merchant API Key.
Further reading
Example
A payment provider sends “invoice paid” twice because its first request timed out. The handler recognizes the event identifier, updates order 1005 only once and avoids creating two customer credits or shipments.
Comparison
A webhook is the provider’s outbound event delivery. The handler is the merchant’s receiving software. Polling is a separate method by which the merchant queries status on demand.
Key Takeaway
Network retries, out-of-order events and invalid signatures are normal design concerns.
Sources
- Webhook — OxaPay (2026-08-03)
- Receive Stripe Events in a Webhook Endpoint — Stripe (2026-08-03)
- CloudEvents Specification — Cloud Native Computing Foundation (2026-08-03)