This is an simple RestAPI application that can be used to generate schema for connecting an Externla Service in Salesforce
I am using OpenAPI 3 to generate docs for API. The application is deployed to Heorku and can be accessed and used with the following link
OpenAPI 3 is supported by Salesfroce prior enabling it through Salesfroce Support. The easiet way is to use api-spec-converter to generate swagger 2.0 format
$ api-spec-converter --from=openapi_3 --to=swagger_2 --syntax=json 'URL' > swagger.json
Open API schema is by default stored as .json file. If you want to convert it to .yaml please use swagger editor. The same editor is a prefred way to validate the schema.
You can navigate through app with HAL browser or swagger-ui. Standard CRUD operations are avaliable to play with an app.