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Editorial Team
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Asked: 2026-05-20T06:42:48+00:00

How does MSBuild decide whether it needs to rebuild a library (that is, invoke

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How does MSBuild decide whether it needs to rebuild a library (that is, invoke csc), or not, when it is run against a C# project file?

I imagine (but want to confirm):

  • If there’s no output directory, rebuild (duh 🙂 )
  • If a C# file has changed, rebuild
  • If an included file marked copy-always has changed, rebuild
    • Or is it smart enough to not rebuild, but just copy the file to the existing output?
  • If an included file marked copy-if-newer has changed, rebuild
    • Same question as above
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1 Answer

  1. Editorial Team

    If you look in Microsoft.CSharp.targets (the MSBuild file for compiling C# projects) the CoreCompile target has a set of Inputs and Outputs defined. These are used to do the dependency checking to see if CoreCompile needs to run. The list of inputs include the C# files, resource files, application icon, strong name key file, and other custom inputs you can define.

    If you have a solution and run MSBuild on it with diagnostic logging enabled (/v:diag command line parameter), you might see this message if the outputs are up to date:

    Skipping target “CoreCompile” because
    all output files are up-to-date with
    respect to the input files.

    The targets file is located in the .NET Framework directory (C:\windows\Microsoft.NET\Framework\v3.5 or v4.0.30319).

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