Microsoft Partially Opens .NET

Microsoft quietly announced Wednesday that it is making the source code for its .NET Framework freely available to developers – but with limits.

Scott Guthrie, a general manager in Microsoft’s Developer Division, made the announcement on his company blog. The source code will be available later this year when Visual Studio 2008 and the .NET Framework 3.5 are released to manufacturing, according to Guthrie’s posting.

“One of the things my team has been working to enable has been the ability for .NET developers to download and browse the source code of the .NET Framework libraries, and to easily enable debugging support in them,” Guthrie said.

The code will be licensed in a manner similar to open source, which the company refers to as the Microsoft Reference License — part of the company’s Shared Source Initiative. A reference license enables developers to look through the source code and use it for debugging purposes but not to change the framework code, recompile it, or redistribute it.

“The intention by releasing these libraries is to provide transparency and allow developers to more deeply understand the inner workings of the source code. Developers who better understand the source code will be more effective in writing software,” Microsoft evangelist Neil Hutson said in his own blog post on the Microsoft Developer Network.

But the move goes beyond simply letting developers browse through the framework’s source code.

“Microsoft will introduce a capability in Visual Studio 2008 to allow .NET Framework developers who are debugging applications, to debug not only into their own source code, but also into .NET Framework source code using Visual Studio,” a Microsoft spokesperson said in an e-mail to

The source code releases will start with the .NET Base Class Libraries, ASP.NET, Windows Forms, ADO.NET, XML, and the Windows Presentation Foundation. Later, the company will add code for the Windows Communication Foundation, the Windows Workflow Foundation, and Language Independent Query, according to Guthrie’s post.

Releasing the source code is overall a good thing, according to one long-time observer, but why now?

“Seven years ago when they introduced .NET, this would have been exciting but now it’s a partial move seven years too late,” Greg DiMichillie, lead analyst for application platforms at researcher Directions on Microsoft told

He pointed to the Flex rich Internet application development platform, parts of which Adobe made available under a true open source license last spring. He also cited Sun Microsystems’ open source release of Java in May.

Both are under much less restrictive licenses than the Microsoft Reference License, allowing free modification and redistribution of source code.

“I give Microsoft a little credit [because] it has some utility, but it’s not a game changer,” DiMichillie said. “It’s read-only and that’s a far cry from what Adobe and Sun are doing.”

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