I don't think you need to add any explicit license at all. Any code you write is automatically copyrighted by you, unless it's a "work for hire" situation. And

I don't think you need to add any explicit license at all. Any code you write is automatically copyrighted by you, unless it's a "work for hire" situation. And no one else has any right to use your work unless you grant it to them explicitly (outside of "fair use" and the like). I'd just slap some "Copyright (2020) - @itqwertz - All Rights Reserved" notices in all the source files and call it done. Of course you have to ask... does it really matter? I mean, if they do use your code, would you ever know about it? And if you did know, would it be worth initiating legal proceedings over?