What is idempotency in API?

Idempotency in an API is a property of an operation whereby multiple executions of the same request lead to the same result and do not change the system's state after the first successful call.

For example, the HTTP PUT method is usually idempotent: if you send a request to update a resource multiple times with the same data, the resource's state will remain unchanged after the first update.

This is important for the reliability and predictability of an API, especially in conditions of network failures, where a client may repeat requests.