What is an API specification?

An API specification serves as a detailed document that defines the functionalities, behaviors, and constraints of an API. It typically includes essential information such as the endpoints available, the methods (GET, POST, etc.) that can be used, the required and optional parameters, request and response formats, authentication methods, and error messages. This level of detail facilitates standardization and ensures that both developers and clients can understand how to use the API effectively.

By documenting the API's features and limitations, the specification aids developers in creating and integrating applications that interact with the API, while also allowing for easier maintenance and updates in the future. This clarity is crucial for collaboration among teams and for reducing ambiguity in the development process, ultimately leading to more robust and reliable applications.

The other options refer to components or aspects of API development that do not encapsulate the full purpose of an API specification. A code library supports development but does not define API behaviors. A testing framework evaluates the performance of an API rather than outlining its specifications. A graphical interface may help in designing APIs but does not serve the role of defining their operational parameters and characteristics.