Source: Legends of Runeterra - Dark Tides of Bilgewater

Wondrous item, uncommon (requires attunement by a spellcaster)

This amulet is shaped like a sword with a small ruby set in the crossguard. Once per day when you are the target of a spell you can use a reaction to cast Counterspell (using your spellcasting ability). Casting Counterspell in this way does not expend a spell slot.