Guy kolbis

I have grown to love working with fiddler. Fiddler is a debugging proxy that allows you to monitor HTTP traffic (requests and responses).

Lately I have encountered an issue within Fiddler that prevented it from capturing HTTP requests that were addressed to the localhost.

After googling it I found Rick Strahl's post that share some light on the matter:

"If you’re using Fiddler with a localhost or 127.0.0.1 address you’ll find that Fiddler will not monitor requests. The reason for this is that local addresses typically bypass any proxies (and the network adapter in general) and so localhost or 127.0.0.1 doesn’t show up.

Luckily there’s an easy workaround for this: Instead of using a local address use the NetBios Machine name or the local IP address:

http://<machine name>/weblog/default.aspx

or

http://<ip address>/weblog/default.aspx

And voila you have access to local addresses."

In addition and for those of you who use Cassini (The Visual Studio Web Server) and want to capture HTTP requests, Rick says:

"What about the ASP.NET local Web Server (Cassini)? There’s a nasty hack for accessing Cassini requests through Fiddler:

http://127.0.0.1.:88/default.aspx

Notice the . after the 127.0.0.1 and before the port number. I’ve only have luck in using 127.0.0.1.  as the domain/address -localhost or the local machine name don’t work."

Another option of using Fiddler and Cassini is putting an extra line in the hosts file:

127.0.0.1 development

Than you can use http://development:<port>.

Additional Resources

• Using Fiddler with Firefox for local web site testing easily with FoxyProxy.
• Localhost HTTP debugging with Fiddler.

I hope this will help.