Idempotent

An HTTP method is idempotent if the intended effect on the server of making a single request is the same as the effect of making several identical requests.

The HTTP specification defines several HTTP methods and their semantics, which includes whether they are idempotent or not. All safe methods are idempotent, as well as PUT and DELETE. The POST and PATCH methods are not guaranteed to be idempotent.

A client can safely retry a request that uses an idempotent method, for example, in cases where there is doubt as to whether the request reached the server. If multiple identical requests happen to reach the server, as long as the method is idempotent, no harm is done.