Its is a huge day for .NET! Microsoft happy to announce that .NET Core will be open source, including the runtime as well as the framework libraries.

.NET Core is a modular development stack that is the foundation of all future .NET platforms It’s already used by ASPNET Core 5 and NET Native I’ll go into more detail on what NET Core is and how it relates to the NET Framework in a following blog post.

This is a natural progression of our open source efforts, which already covers the managed compilers (C#, VB, and F#) as well as ASP.NET:
  • C# & Visual Basic ("Roslyn")
  • Visual F# Tools
  • ASP.NET 5
  • Entity Framework
This takes it to the next level by extending it to the .NET run-time and the core framework.
The new .NET Core stack will be entirely open sourced on GitHub. We already made the necessary engineering changes for some of the libraries and included them in the core framework repository. Between now and Build 2015 you can watch us as we’re making progress.

In order to play with our bits or experiment with your own modifications you need to be able to build and run your own version of the libraries. We want to make this as easy as pie, so here it is:
  • You clone our repo (git clone
  • You invoke build.cmd
The build only requires Visual Studio 2013 (i.e. it doesn’t require “Dev14”). It will build all the libraries and run the unit tests.
One of the challenges Microsoft had in the past was around strong naming which prevented you from simply dropping a binary into an existing project. Microsoft addressed this concern by providing a new way to strong name binaries, which we call open source signing.