Recently I posted about Charles Web Debugging Proxy and quite a few people mentioned they had been using Fiddler.
Fiddler is a Web Debugging Proxy which logs all HTTP(S) traffic between your computer and the Internet. Fiddler allows you to inspect all HTTP(S) traffic, set breakpoints, and “fiddle” with incoming or outgoing data. Fiddler includes a powerful event-based scripting subsystem, and can be extended using any .NET language.
Fiddler is freeware and can debug traffic from virtually any application, including Internet Explorer, Mozilla Firefox, Opera, and thousands more.
If you want some info on how to use Fiddler for debugging you can check here:
You can download Fiddler here:
Or read more here.