API description done with Swagger aka OpenAPI.
For more information about OpenAPI, see the documentation.
In order to improve the API description, you can use the online swagger editor. Just copy and paste the openapi.yaml.
Its also possible to run your own editor in docker:
docker run -d -p 80:8080 swaggerapi/swagger-editor
See: https://github.com/swagger-api/swagger-editor
Also a nice tool for expanding the api-description: https://openapi-map.apihandyman.io/