How to display localhost traffic in Fiddler while debugging an ASP.NET application?

try using this:

http://ipv4.fiddler/folder

instead of

http://localhost/folder

this also works with ports

http://ipv4.fiddler:12345/folder

Here is link to fiddler documentation

http://docs.telerik.com/fiddler/Configure-Fiddler/Tasks/MonitorLocalTraffic

For an ASP.NET web site project:

1) Right-click the project and select Property Pages
2) Select Start Options
3) Under the Server section, click the "Use custom server" and edit the Base URL by replacing localhost with your computer's name.

Probably the easiest way to monitor traffic to localhost is to replace "localhost" with "localhost." in the browser's URL bar. E.g.

http://localhost./MyApp/default.aspx

Check out this link...the 'workaround' is hacky, but it does work:

Tip for using Fiddler on localhost

You may use PC hostname instead of 127.0.0.1 or localhost

Ensure that in your Fiddler Connections that localhost isn't in the "IE should bypass Fiddler for URLs that start with:" box.

You should uncheck the checkbox:

Bypass proxy server for local addresses

Located at proxy configuration of Internet Explorer.