Decribing APIs - describe RESTfullHTTP API in a machine readable way:
Produce API reference documents
Auto-generate code SDKs
Use description in other developer tooling
OpenAPI - API description language formerly known as "Swagger", an open standard, supported by industry.
Spec-First API design
That's what’s magic about it - it is open, there is so much that you can do about it.
The project you don't just ship but live and evolve.