What is Fiddler?

For last few months I have using Fiddler for my testing. Actually I used to test some hybrid application where a desktop application interact with multiple online servers for different purposes. So Fiddler helped me to track different http calls between desktop and online servers.

Fiddler is a HTTP Debugging Proxy which logs all HTTP traffic between your computer and the Internet. Fiddler allows you to inspect all HTTP 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.

Fiddler is the electronic equivalent of an X-Ray that can get into the traffic going between your web application and the web server to make sure that everything is OK. Fiddler can tell you what was wrong in a specific interaction and can show you at a glance what problems there are with the overall conversation. It's an invaluable tool for anyone who develops web applications — no matter whether that development is in .NET, Java, Cold Fusion, or some other language.