Fiddler is a Web Debugging Proxy which logs all HTTP(S) traffic between your computer and the Internet. Fiddler allows you to inspect 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
that supports a proxy, including Internet Explorer, Google Chrome, Apple Safari, Mozilla Firefox, Opera, and thousands more. You can also debug traffic from popular devices
like Windows Phone, iPod/iPad, and others.
I like this tool very helpful because, it lets any person, needless of automation engineer, even a developer, manual test engineer to debug and trace the traffic going in and out between your browser and the webserver.
You can download fiddler from here