How To Customize Web.Config in a C# Project using Visual Studio 2010

VS2010 can transform your web.config file before each compilation and before launching any 'Run/Debug'.

Picture 01

Step 1: On your project, locate the visual clue that the web.config file actually ... has children.  Pay attention to the Solution Explorer window (pic. 01).  Notice that the file has a little arrow head to its left, suggesting it can be expanded.

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Step 2: Expand it now please.  You should see one child per each "Solution Configuration".  Usually, the default is "Debug" and "Release".  You should be seeing something like picture #02.