Swagger is a very popular specification format for web-based APIs which can be used with a growing list of both open source and commercial tools - for example to auto generate client program code to access the API (in almost any programming language).
We have just released Simple DNS Plus v. 6.0 build 106 (available at https://simpledns.com/download) which includes an API specification file in Swagger format for the Simple DNS Plus HTTP API along with a copy of Swagger UI - both available via the HTTP API (see links on HTTP API root default page - typically at http://127.0.0.1:8053).
Swagger UI is a dynamic web-page that makes it easy to explore and play with any API that has a Swagger specification file.
Screen shot of Swagger UI with the Simple DNS Plus HTTP API specification file loaded:
You try this with the Simple DNS Plus specification at https://simpledns.com/swagger-ui but you need to load it from your own instance of the Simple DNS Plus HTTP API in order to use the "Try it out!" buttons (sending requests to the API).
One way to generate client program code for the Simple DNS Plus HTTP API (or any other API with a Swagger specification file) is to open the specification file in the Swagger Editor at http://editor.swagger.io and then select your preferred programming language in the "Generate Client" menu...