I have environment with VS 2013 and VS2015 installed and we are working on huge projects. Currently I can observe very wired behavior when building over VS2013 development command line lead to situation when FxCop violations are not reported. Building same project in VS2015 development command line will fail build with 3 FxCop violations (correctly). WE have custom rule set defined with inheritance hierarchy as well as custom FxCop rules binaries. We can se same behavior in VS itself. While building over VS2013 FxCop violations are not reported. While building over VS2015 build will fail because of FxCop violations. WE are using 2013 FxCop engine and task definitions while using VS2015 and corresponding msbuild. This was done to avoid situation where custom FxCop binaries need to be re-build for usage with VS2015 (previously build with VS2013). This was achieving by copying content of c:\ProgramFiles\MSBuild\Microsoft\VisualStudio\v12.0\CodeAnalyses to v14.0 location.