How do I make an entity unspawnable?

So I know how to do this and I don't, so I was wondering if someone could make me a Descriptor and a Spawn command that won't allow users to spawn entities that have the tag, <UnSpawnable/>. If you do this and want credits say so I will credit and link your MPGH!

@ManKindGaming why would you want to keep an entity in-game that is unspawnable for anybody (i suppose except you or lol xd)

you can modify the /spawn command tho, it's easier and there are alot of threads how to do that (they're for the annoying vaultchest, but for other entities it stays the same)