Today I needed to inspect the webtraffic to my WCF webservices, Fiddler was not able to see my webtraffic to localhost.
To use fiddler with localhost these steps needs to be done:
1. Disable IPv6 in Fiddler configuration.

Fiddler settings
2. Add <computername> to your hosts file and set it to 127.0.0.1.
127.0.0.1 <computername>
3. request your webserver with http://<machinename>:<portnumber>.

Fiddler Traffic