<p>A unique, client-generated idempotency token that, when provided in a request, ensures the request cannot be repeated with a changed parameter. If a request is received with the same parameters and a token is included, the request returns information about the initial request that used that token.</p> <note> <p>The AWS SDKs prepopulate client request tokens. If you are using an AWS SDK, an idempotency token is created for you.</p> </note>