Fiddler is a web debugging proxy tool. Being a proxy, it redirects all traffic going from your computer to the Internet. This way, we can inspect the contents of the packages being sent over the wire. Fiddler also works for inspecting traffic to the local web server (ASP.NET Development Server or local IIS).

While developing with Silverlight in combination with services, Fiddler is a valuable tool. Without a debugging proxy, it's not possible to see what data Silverlight is sending to the service or to see the response coming back from the service. In this book, we show the usage of Fiddler several times. In your daily development life, Fiddler can help you track bugs when building Silverlight applications that work with services.