Cat licked chocolate fudge brownie batter.

I turn my head for two seconds and the bastard sticks his tongue in there. I know chocolate is toxic to cats, and it’s fudge brownies. Would I be overreacting by taking him to the vet? It was just a few licks. He’s roughly 3 years old and about 13 lbs, he’s fat. He’s a former feral and probably ate much worse on the streets but I don’t want him getting sick. He’s also kinda dumb, and way too curious for his own good. I have no idea how he survived in the wilderness for that long.