Why Webhook Idempotency Matters and How to Implement It Safely

Webhook providers typically use at-least-once delivery, meaning the same event can be sent multiple times due to network failures, timeouts, or unconfirmed responses. Without safeguards, duplicate deliveries can trigger repeated business actions such as double charges, duplicate orders, or redundant emails. Comparing payloads or hashes is an unreliable fix, as two distinct events can carry identical data. The standard solution is an idempotency key — a unique identifier sent with each request that the receiving system stores and checks before processing. By rejecting any request carrying a previously seen key, applications ensure a retry never repeats the underlying business action.