Update: You may also be interested in Testing Express.JS REST APIs with Mocha.
Tools used to test HTTP-based REST APIs include command-line utilities like curl and wget, as well as full-featured test frameworks like Mocha. Another interesting option is RESTClient, a plugin for Firefox that provides a user-friendly interface for testing REST APIs right from your browser.
Selenium IDE is used to run tests on regular web pages, but I've never seen it used to control another Firefox plugin before. I gave it a try and discovered that it does this beautifully. Here's a picture of Selenium IDE driving RESTClient.
It's pretty cool to see Selenium IDE driving the RESTClient …