Lorna Jane gives a good overview of the tools available when working on an API.

As Web Developers, we need to know how to work with HTTP from every angle. I gave a 2-hour tutorial at PHP UK that included some of my most trusted tools - but it was sold out and a bunch of people asked me if there was video (there wasn't, tutorials make little sense when videoed). Instead, I thought I'd try to set out a self-study version of the workshop (I rarely teach these days so I'm unlikely to deliver it anywhere else).