Developers use .NET Reflector VSPro to:

Debug assemblies without source code using the Visual Studio debugger
Decompile and explore .NET assemblies inside Visual Studio
Serve as a powerful object browser
Decompile .NET code to understand how it works
Learn or teach the complexities of a .NET language
Provide a better alternative to library documentation
Recover lost or unavailable source code
Locate performance issues
Analyze dependencies
Check obfuscation

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Home Page: http://www.reflector.net/