Is there a way to indicate that a homebrew monster is a swarm? Are we limited to just the swarms that already exist in the game?

First you have to designate a “swarm type” so it knows what it’s a swarm of:

So if you were to select lizard, it would be a swarm of lizards. Then you have to fill in the information and everything just like a regular monster and don’t forget to add the “Swarm” special trait to it too.

So I started with this👉lizard as the template and quickly turned it into this👇swarm:

I hope that helps.

Edit: Statblock updated

So I'm just looking for a creature in that dropdown that's the same size and type as the one that I want to create in order to get it to abstract it to "Medium swarm of <size> <type>", then? Thanks for the info! I'll try it out.

Worked like a charm. Thanks!

I forgot before with that swarm of lizards, but every swarm is supposed to have the following too: