The problem with WTFPL is that it's not clear that it lets you do the things that copyright usually prevents you from doing. In particular: * It's not explicit

The problem with WTFPL is that it's not clear that it lets you do the things that copyright usually prevents you from doing. In particular: * It's not explicit that the user can redistribute the software freely. * It's not explicit that you're free from warranty, meaning that, unlike basically all code ever written, you're on the hook for bugs and defects, just like a physical product. Yes, it does say "do what you want," but that's not necessarily good enough for lawyers.