In theory, localhost connections in Metro applications are not possible unless connecting to the same app – but how about in practice?

As you might know, Windows 8's Metro applications have strict limits enforced by the operating system on what these applications can do. For instance, communication between Metro applications and regular desktop application and services is prohibited. Even if you would open a local TCP port (or HTTP endpoint) from a desktop application and try to connect to that from your Metro application running on the same computer, that would not be doable.

For testing purposes however, it is possible to temporarily lift what is called a loopback connection restriction. You won't be able to distribute software that does this through the Windows marketplace once it opens for Metro applications, but for testing, development and debugging work, it might just well be what you need.

This is the theory, but the interesting thing I noticed is that at least between two .NET applications (say, a ASP.NET application running with IIS Express and a Metro application), localhost connections work just fine without anything special. Hmm!