Use Fiddler to view traffic when running locally…

If you haven’t used Fiddler, you should check it out. It shows you the HTTP traffic that is flowing over the wire. This can be a huge help when diagnosing issues.

One small challenge is using Fiddler to view traffic that stays on the local machine. By default, fiddler cannot see data sent to http://localhost/ or This is because the OS doesn’t push this data through the normal networking pipeline.

One workaround is to use the name of your machine in the URL. So, if you have a machine named “Machine1”, you could use a URL of http://machine1/. The problem is that the visual studio “local web server” only accepts connections from the local machine.

What to do?

When running fiddler, you can use an alternate format for the local machine. In your config files, replace http://localhost with http://ipv4.fiddler. It looks strange, but it works.

Once you do this, you can have a web site (or unit test) call into a web service that is running locally and the request will show up in fiddler.

Here’s the help page from Fiddler’s site:

Cool! Wish I had figured that out about 6 months ago!

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