Modern software systems, often inherently distributed, face challenges like network partitions that can lead to issues such as duplicated operations when requests are retried. Idempotency, the concept where requests can be safely repeated without unintended effects, offers a solution to this problem. Knock has developed "One and Done," an Elixir library supporting idempotent requests, particularly for applications using the Plug web framework. This library, designed for ease of use and flexibility, enables applications to handle repeated requests efficiently by caching responses based on a unique Idempotency-Key. It can be integrated with any compatible cache and supports various web frameworks. The library, permissively licensed under MIT, encourages contributions and provides extensive documentation for implementation. Knock’s SDKs across multiple languages already support idempotency for workflow triggers, with plans to expand this feature to other API endpoints.