Psalm is an amazing static analysis tool made by Vimeo. It can detect type errors, dead code, usages of unknown classes and much more. In this video you'll learn how to use it within the context of a package. After you've seen the video, you should definitely do some research on the checks that Psalm provides and which ones are helpful for you.
If you use our PHP Package skeleton repo or Laravel package skeleton repo, than everything shown in this video is already set up.