Today when I tried to use the RestClient in my freshly installed rails project I got an err. Then I thought I had to import it so I did require 'rest-client' and also got an err. But when I installed it in my gem file and then the problem resolved.
There is no support for rest client gem in the Rails. You can check the Gemfile. I assume you are talking about the Ruby gem, if so, you can find all related information in the documentation for rest-client gem.