I use CGI::Application::Dispatch quite heavily, and my workflow generally includes fleshing out the request handling and responses using something like the Chrome's REST Console.

Once I have that fleshed out, I like to us YUI 3 (specifically Y.IO) to build out one of many possible client interfaces.

The important message here is the workflow. The tools mentioned are what I use, but you can use anything. It's best to work out the REST API first, without the UI being built up along side. Once you get the API and build up your first (of many) REST consuming clients, then you might have to slightly adjust your API if done right, but you don't want to be molding your hopefully long lived REST API with what will be a relatively much shorter lived client.