Building web applications is hard work and most people remain unaware of how their web application is interacting with the web browsers that their clients have installed. Fiddler, a free web debugging proxy created by Eric Lawrence, helps to simplify the analysis process substantially by logging all HTTP(S) traffic between your computer and the Internet. Fiddler is a transparent proxy that automatically adds itself to the WININET chain so that it can see every request being made. It logs those requests and the responses to allow you to see what is working and what isn’t working.
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.
The developper, Eric Lawrence, is Security Program Manager at Microsoft for Internet Explorer.
A quick summary of getting started with Fiddler has been published at Developer.com. A detailed documentation is available at the Fiddler website. A discussion forum and a developer section are available at the same site. Various addons and third-party extensions have been developped.
Fiddler can be configured to analyse the http traffic of iPad’s, iPhone’s and other web devices.
A simular tool called Charles is available for Mac Computers.
Some related tutorials about HTTP debugging are listed hereafter :