dotPeek: free .NET decompiler from JetBrains, the makers of ReSharper, dotTrace, and dotCover for .NET developers, as well as a family of IDEs for Java, Ruby, Python, PHP, and other languages, plus team development tools: TeamCity and YouTrack.

dotPeek goes public for the first time on Tuesday, May 10, as JetBrains open an Early Access Program that implies regular publishing of pre-release builds.

JetBrains are also about to include decompiling functionality into their forthcoming release of ReSharper 6. In fact, decompiling has been announced as part of ReSharper 6 back in February 2011, and available in ReSharper 6 pre-release nightly builds since then.

General features

What can be opened?

dotPeek decompiles any .NET assemblies and presents them as C# code. Both libraries (.dll) and applications (.exe) can be opened with File > Open assembly.
In addition, assemblies from GlobaL Assembly Cache can be opened via File > Open from GAC. One thing to note about the Open from GAC dialog is that you can batch-select assembly items there, and you can also filter out assemblies by entering their CamelHumps - the capitals that different parts of assembly names start with. for example,

How is decompiled code presented?

As C# code.
dotPeek provides an assembly explorer to traverse the list of opened assemblies
Look-and-feel of Visual Studio:

The idea behind dotPeek is to bring ReSharper experience to browsing external assemblies and make this available to everyone. That essentially means that the main thing that distinguishes dotPeek from other decompiler around is that the majority of navigation features from ReSharper are available in dotPeek as well. Let's take a closer look at those:

Navigation features

Other features