1 reaction, which you take when you see a creature within 60 feet of you casting a spell
You attempt to interrupt a creature in the process of casting a spell. If the creature is casting a spell of 3rd level or lower, its spell fails and has no effect. If it is casting a spell of 4th level or higher, make an ability check using your spellcasting ability. The DC equals 10+ the spell’s level. On a success, the creature’s spell fails and has no effect.