CleanInstaller (or Custard) by Delphy@MTS is a tool that helps you analyse downloaded Sims3Packs before you install them. You can either remove stuff you don’t want in your game or decide to not install the Sims3Pack at all. Since Custard is still Alpha (and probably will be forever), you should always work on a copy of the file so if anything goes wrong, you can try again. If you only want to check without changing you can do that on the original file.
Custard can only analyze single Sims3Packs and you can’t analyze Sims3Packs that are already installed either. Custard does only show a few of the errors it can actually detect as errors so you should know what to look out for.
The tutorials in this section should help you identify the errors.