Fiddler is a comprehensive web debugging proxy that keeps detailed track of all HTTP connections and the data exchanged between your computer and the web server. The program allows you to inspect traffic, set breakpoints, and manipulate incoming or outgoing data. Fiddler includes a powerful event-based scripting subsystem, and can be extended using any .NET language.
The program can debug traffic from virtually any application that supports a proxy connection, including IE, Chrome, Safari, Firefox, Opera, and many others. You can also use Fiddler to debug traffic from popular devices like Windows Phone, iPod/iPad, and others.