Depends on what you’re compiling/running in your other project, but the only other thing I can think of at the moment is that your Toolbox.uplugin lists the Toolbox module as Type “Editor” - if your other project references Toolbox code in non-editor builds (e.g. Development Game or Shipping), then the module will be missing because it’s been marked to not load except in Editor builds. If this is the problem you just need to either change the Type in Toolbox.uplugin, or you need to wrap #includes and related code with #if WITH_EDITOR