For more details, instructional videos and download, visit www.fiddler.com.
In a previous blog I mentioned the free Wireshark utility, which has been my number one debugging tool for several years. Being able to see everything coming into and out of a PC, and having enough network background to glean the important details, has served well. During a recent problem I needed to debug a web application that only ran using encrypted (https/ssl) communications. Wireshark was able to show me what was happening with session setups and encryption exchanges, but all the application data was just a garble of meaningless characters. Enter Fiddler, a free tool provided by Microsoft.
Launching Fiddler can be via its shortcut or from Internet Explorer using the Tools ... Fiddler2 option. Fiddler will automatically change Internet Explorer's proxy settings, which also affects all other applications, like the Google Chrome browser, that use the same settings. Mozilla's Firefox, which does not use IE's proxy, can be controlled via an option installed in the lower right-hand corner.
Capturing and displaying encrypted data requires changing some default options, located under Tools ... Fiddler Options ... HTTPS tab. I suggest you read the information found at the "Learn more about HTTPS Traffic decryption and certificate errors" link.
Fiddler has a number of features, more for the professional developers and tester, that go way beyond simply displaying data. You can set breakpoints and even fiddle (hence the name) with the data and inject your own. But just seeing what's really going on "behind-the-scenes" can be eye-opening.
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