The main goal of this class is to produce a collection of ApiDescription. It does so by statically inspecting the routes and the available actions inside your controllers. Each ApiDescription describes an API that is available on your service. As you can see from the simplified class diagram below, the ApiDescription contains basic information such as the HttpMethod, the RelativePath, the Documentation, etc. But it also points to anActionDescriptor which is part of the core Web API component that knows everything about an action. You can use it to access a lot more information such as the action name, the return type, the custom attributes, etc. Similarly, you can access the ParameterDescriptor for the expected parameters.