What should API documentation include about inputs and outputs?

• A. They specify only the color of the UI.
• B. They define expected input types, output types, and behavior for public APIs.
• C. They are optional and can be omitted.
• D. They describe the build steps.

Answer: (B)

Clear API documentation centers on the contract between the caller and the API by detailing what you provide and what you receive. It should specify the expected input types and shapes, which fields are required versus optional, valid formats, and any constraints or defaults. It should also define the output types and shapes, what data is returned on success, and how errors are reported, including status codes and the structure of error messages. Including concrete examples of requests and responses helps developers implement and test against the API, and it supports client libraries and validation tooling. The options that focus on UI color or build steps miss the core purpose of API docs, and treating documentation as optional would leave developers guessing about how to use the API.