You do need a license of some sort. BSD, MIT, and similar are about as minimal as is advisable. You need a disclaimer of warranty so that you're not liable if

You do need a license of some sort. BSD, MIT, and similar are about as minimal as is advisable. You need a disclaimer of warranty so that you're not liable if your software breaks someone's system, and the user's right to use your software needs to be conditional upon accepting the disclaimer.