Using Fiddler in a Windows 8 Metro Style App

Fiddler is one of the tool that every software developer needs when developing for the web or more particularly for an API. In Stacks I have use it heavily when debugging the OAuth process and signature of the Instapaper API.

In Windows 8 your app is running in a sandbox environment. Even your unit test project has a runner which mimics the Windows 8 Metro style app environment.  This isolation prevent Fiddler to receive data since the app is forbidden to access the loopback on the local computer.

Since the .NET runtime 2.0 is not installed, you will need a beta version with support .NET 4.0 support. After the installation you can use this add-in which will add a menu (Win8 Config) in the toolbar.

You will need to launch it after running your app, check it and save the configuration. After restarting Fiddler you should be able to see the network traffic: