Actually there are two pulleys to check... The tensioner and the Idler
Not trying to be a dick here, but I'm not sure of your technical level so... DON'T check them while the motor is running!
Loosen the tensioner and take the belt out of the way. check for looseness and overall slop. They should not make noise when turned and should spin freely without a feeling of roughness when they are turned by hand. When new, they spin freely when you turn them but do not continue to spin when you let them go.
But I really don't think this is your problem, but it never hurts to check em anyway, especially if the Jeep has any miles on it.