An API can have great value, but it won't gain traction unless developers know how to use it. Developers want to integrate an API as quickly as they can. Good API documentation helps a developer understand the API's capabilities and how it should be used, making integration more efficient.
OpenAPI is a specification used for describing REST APIs. It is language agnostic, and allows you to describe your entire API including:
Available endpoints Operation parameters Authentication methods Contact and other information You can write API specifications in YAML or JSON. With the OpenAPI specification, humans and computers can understand the capabilities of your API without having access to its source code.