Have you ever found yourself wondering how Internet Explorer interacts with your Web application? Have you encountered a strange performance bottleneck that you can't track down? Are Nitobi components not working, and you're wondering if the server is causing an error you can't see?
Microsoft Fiddler can help you answer these questions, and many more. Fiddler is an HTTP debugging proxy that logs all HTTP traffic between your computer and the Internet. Fiddler enables you to inspect all HTTP traffic, set breakpoints, and "fiddle" with incoming or outgoing data. Fiddler is much simpler to use than NetMon or other network debuggers because it exposes only HTTP traffic and does so in a user-friendly format.
Open up Internet Explorer, and you'll see the Fiddler icon in the toolbar. Click on it.
When the Fiddler window appears, you will see a split-view, with individual HTTP requests listed on the left side, and details of these requests shown on the right hand side.
Switch back to Internet Explorer and begin playing with your Ajax application. Try to trigger some data requests.
Switch back to the Fiddler window now, and you will see your data requests listed down the left side. Click on one of them, and then click "Session Inspector" on the right-side.
In Session Inspector you will see a view similar to this:
Click on "Raw" or if thats not available, "Textview" in both the top and bottom panes.
You should now be able to see the exactly text that was transmitted to the server in the form of Form posts or Querystring requests, and the response that was sent back from the server. In this way you can detect if the server is outputting errors, or proper data. This is also helpful for troubleshooting all manner of 404 and 500 errors.
