In ASP.NET projects you can tranform Web.config files out-of-the-box in VisualStudio.
When you want app.config files and .xml files transformed in the same manner you can use SlowCheetah.
First download and install the SlowCheetah.vsix.
Then VS – Tools – Extensions and Updates:
Now you can add files under App.config and preview transformation changes.
Next you can add this pkg to your projects:
– Rightclick refs – Manage Nuget pkg’s – search online for SlowCheetah
Now you can build your project with the transforms included.