Once you've ironed out all of the bugs in an ASP.NET AJAX Application, you'll probably want to perform other types of tests to ensure that the application performs as expected. It's difficult to know how an application truly performs unless you take the time to look at some of the request and response messages being sent from the client to the server. By looking at the raw message data, you may discover ways to minimize the size of the messages and speed up the request/response mechanism. It's also important to see the actual request and response because this is a 100-percent authoritative view of what communication is actually taking place between the browser and Web server; if this appears different from what you intended, it can alert you to bugs.
Several free and easy-to-use tools exist for inspecting request and response messages. The next sections introduce several such tools, including Fiddler and the Web Development Helper.
Fiddler is an excellent tool created by Microsoft's Eric Lawrence that can be used to inspect AJAX messages exchanged between the client and server. It can be downloaded from www.fiddlertool.com and is free to use. It provides a simple and effective way to view many different details about messages, including request and response headers, raw message data, message sizes, and other useful information.
After Fiddler is installed, it can be accessed directly ...