If you have been tried using Fiddler in localhost of Visual Studio inbuilt Web Server called Cassini, you mite have noticed that you will receive a HTTP 502 error. Saying [Fiddler] Connection to localhost failed.

To solve this you might try adding period (.) after localhost as shown below.

For some machines it seems to work but some it doesn’t. In case in yours it doesn’t work try changing localhost to 127.0.0.1 and then adding period (.) after it.