Fiddler is a program that allows to visualize and to analyze the requests http and https initiated from the navigator, to control the traffic; And for web developers it is a useful tool for testing scripts, Ajax calls, and so on.
The application contains two windows: one in which you can see all the requests; And another window to the right where you can see the details, such as the header and other information of each request and its corresponding response from the server.
In DownloadSoft we had presented a similar application called Firebug that is integrated with Firefox, whereas Fiddler can be used with any browser, like Internet Explorer, Opera, et.
Fiddler 188.8.131.52 is the latest version available, updated in May 2012. It works for Windows and can be downloaded for free. Requires .NET Framework 2.0.