Need "getting started" documentation for rails-api only developers

As more and more groups move away from developing traditional monolithic Rails apps and move to developing JS-frontend-rest-backend apps, there will be more new potential Rails users like me. We want to use Rails exclusively for developing REST services. I’m finding it impossible to locate good “getting started” documentation for this class of users. I think there needs to be something like http://edgeguides.rubyonrails.org/getting_started.html for users that only want to develop REST APIs. Certainly, the docs at http://edgeguides.rubyonrails.org/api_app.html are really not helpful at all if you don’t already know Rails. Even if you do know Rails, there is no step-by-step material on how to build REST APIs.

Can anyone point me to relevant documentation that I’ve missed?

Are we mistaken in our goal of using Rails for API development only?

Would we be better off using something like Sinatra, where it is much, much easier to get started developing REST APIs?

Thanks for any help!

Rails API in Rails 5 is just a small convenience, serving JSON to API clients is something people have routinely done in Rails for years.

Are we mistaken in our goal of using Rails for API development only?

Would we be better off using something like Sinatra, where it is much, much easier to get started developing REST APIs?

These questions are worded as if you were the potential customer a salesman could loose. Rails is not a comercial product, Rails owns you nothing. And if you feel docs are missing here’s your opportunity to contribute to the project.