API documentation is a collection of materials that provide users with the necessary information to effectively build apps using your API. It should include API reference documentation, examples of using the API, error messages and status codes, basic usage guides, tutorials for more complex scenarios, and other supporting materials. Good API documentation is essential because it enables users to discover how to use your API, understand its functionality, and handle errors effectively. It also provides a reference point for developers to build SDKs against your API. The best place to write API documentation is in the API itself, using standards like Swagger or OpenAPI, which can be generated automatically by frameworks like FastAPI. To ensure high-quality documentation, it's essential to have a dedicated technical writer or someone responsible who can maintain and update the documentation regularly. Additionally, good API documentation should be clear, concise, and accessible, with code samples, tutorials, and guides that cater to different learning styles. By following these best practices, you can create an SDK that is better than your original API.