This is a completely amazing tool that does everything but capture the communications between the source and the target for analysis. (if it could do that like Cellist...)
I have been using this tool for months and the feature set, capability and utility are superb. I have downloaded all other similar 'free' and "In app purchase" style competitors and none come close to comparing against Paw.
Paw builds the HTTP (REST or really SOAP too) requests, allows you to execute them, even in some instances lets you chain response data from one response as input to another request.
If you don't know how HTTP URL parameters, body parameters, forms, Oauth work (or even think you do) Paw is an excellent playground to experiment and learn. It is as much as of an interactive learning tool as it is a development tool (sign of good software, is how PageMaker launched the era of Desktop Publishing)
Now if that was not enough, Paw can then teach you how Cocoa in Objective C or Swift works with NSURLConnection or NSURLSession classes by using the real-time code generation plugins to see the code generate as you change the URL parameters.
Paw is like having a second team-mate, or a kindly mentor there working with you.
Paw is not cheap at $50... but it is only expensive if you time is worth nothing with cheaper tools.
And don't forget to check out Paw Prints, the interactive web tool account that comes with Paw.
Best software purchase I made in 2016 at any price. And if it could capture HTTP traffic with a MTM function and generate the REST calls... that would be amazing.