I have a REST service written in C++/Qt. I'd like to create REST API documentation (using application like Postman for Open API) in order to help a front-end developer who will create rich-client app based on Vue.js. Is it possible to minimize efforts using JSON feed (output from some REST methods)?
Why don't use swagger? You can generate openapi 3 json and then use swagger tools to generate the UI or stubs.
There is also the inspector tools (but is is pro) that should be what you need.