Simply put, an API directory is essentially just a list of available APIs.
API directories help developers search for APIs or hear about new and interesting APIs.
An API directory will have a wide variety of APIs and information about each API. Usually, API directories also have categories to help aid API discovery.
An API directory might also consolidate tutorials and other resources to help a developer get started with the API.
Why Use an API Directory
Even though you can not directly consume APIs through an API directory it can still be a useful tool to find or compare APIs. A directory can also be a good place to find alternative APIs to replace a deprecated API or an API that is too expensive for your budget.
If you find an API you want to use in the directory, it will probably provide information on how to consume the API through the official provider or a third-party provider.