LEARN · WEBHOOKS
Your webhook worked. Then it worked again.
A practical guide to signature verification, idempotency, duplicate events, retries, and building webhook handlers that behave safely in the real world.
Webhook systems are easy to demo and surprisingly easy to get wrong in production. The dangerous case is not always a failed webhook. Sometimes the dangerous case is a successful webhook that runs twice.
Why duplicate delivery matters
Providers retry events for good reasons: timeouts, transient failures, uncertain acknowledgements, and network problems. Your application has to assume that the same event may arrive more than once.
1. Verify the sender
Before processing the event, validate the request signature using the provider's signing secret. Signature verification helps you reject forged requests and confirms the payload has not been altered in transit.
2. Make processing idempotent
Give each event a durable identity and record whether it has already been handled. If the same event arrives again, return a successful response without repeating side effects such as charging a customer, creating an order, or sending a notification twice.
3. Separate acknowledgement from side effects
Keep the webhook path predictable. Validate quickly, decide whether the event is new, and make side effects resilient. The goal is to avoid turning a temporary provider retry into a duplicate business action.
4. Test the unhappy path on purpose
Send the same payload twice. Break the signature. Simulate a timeout. Replay an event. Good webhook testing should prove that your handler remains safe when delivery is messy.
SUGAR BYTE
Reliable integrations assume duplication, delay, and failure.
If your webhook design only works when every request arrives exactly once and in perfect order, it is not production-safe yet.
What this demonstrates
This pattern combines API security, reliability, testing, and developer experience. It is also the foundation for the Show-Ready Checkout project, where HMAC verification, idempotency, and automated tests are used to make duplicate delivery observable and safe.