# Idempotency and the X-Event-ID Header

# Idempotency and the X-Event-ID Header

`X-Event-ID` is added as a header to the request. It is a unique identifier assigned to each event.

* **Uniqueness**: Each `X-Event-ID` value will be globally unique for each event that occurs.
* **Re-Delivery**: Events are delivered **at least once**. We will redeliver events on failure due to network issues, timeouts and listener errors. The `X-Event-ID` will remain the same across retries.
* **Idempotent Processing**: We recommend that you use the `X-Event-ID` to handle events in an idempotent way. If you encounter the same `X-Event-ID` again, simply skip and acknowledge the duplicate event rather than processing it a second time.