How to Handle Duplicate Webhook Events with Idempotency

Duplicate webhook events are a common and costly problem — for example, a payment handler that lacks idempotency checks can charge a customer multiple times if a provider retries delivery after a network timeout. The root cause lies in the fact that network failures, provider retries, and server restarts can all trigger the same event more than once. The solution is to build idempotent webhook handlers that produce the same outcome regardless of how many times an event is processed. This is achieved through three core principles: extracting a unique event ID from each payload, storing processed event IDs in a database or cache like PostgreSQL or Redis, and structuring business logic so repeated execution causes no side effects. Providers such as Stripe, GitHub, and Shopify each include a stable unique identifier in their webhook payloads, which serves as the deduplication key.