For those who do not already know Lutz Roeder's .NET Reflector, it is a free and excellent .NET assembly browser and analyzer and also a disassembler and decompiler for a lot of .NET languages.

The Reflector addin for SharpDevelop provides a bridge between SharpDevelop and Reflector, so that you can directly start Reflector from the context menu of the source code editor and view the selected code element:

When you select the "Open .NET Reflector" item, the addin will start up Reflector or connect to an existing instance if it is already running. After Reflector has started up, it will be positioned on the best match for the selected code element:

The same functionality is also available from the class browser of SharpDevelop:

When you use the addin for the first time, you have to tell it where to find Reflector. For this purpose, the following dialog will pop up:

There you will also find the download link for Reflector, in case you do not have it already. Then you have to enter the full path to Reflector.exe into the text box or locate it using the browse button.

The entered location will be saved, but the dialog will appear again if the addin can no longer find Reflector at the saved location.

Note that SharpDevelop must have write access to the folder containing Reflector.exe because it has to copy and possibly modify some files there. Have a look at the internals if you are interested in the details.