Shield

From Player's Handbook, page 275.

Description
1st-level abjuration


 * Casting Time: 1 reaction, which you take when you are hit by an attack or targeted by the Magic Missile spell
 * Range: Self
 * Components: V, S
 * Duration: 1 round

An invisible barrier of magical force appears and protects you. Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack, and you take no damage from magic missile.

Learned By

 * Classes: Sorcerer, Wizard
 * Subclasses: Artificer (Artillerist), Artificer (Battle Smith), Fighter (Eldritch Knight), Rogue (Arcane Trickster), Warlock (The Hexblade)
 * Races: Githzerai