You touch a willing creature who isn't wearing armor, and a protective magical force surrounds it until the spell ends. The target is granted +3 to AC for the duration. The spell ends if the target dons armor or if you dismiss the spell as an action.

At higher levels. When you cast Archmage's Armor using a spell slot of 3rd level or higher, the target gains +1 to AC for each level above 2nd.