My cat ate a cooked chicken bone. I don't know if this is dangerous. Is it OK or should I make sure this never happens ever again.

Which bone? Leg or wing or what? Is the cat acting okay?

NO, cats should not eat chicken bones.

Cooked bones can splinter and obstruct the intestines or rip the stomach.

This sounds like an accident, but please ensure that your animals cannot consume cooked bones.

Keep a close eye on your animal. Any type of strange behavior such as excessive sleeping, open-mouth panting, pain in the abdomen, and unproductive vomiting. If any of that occurs, you need to contact your vet immediately.