The Grimoire is operated by, Dice Bard has everything you need to play 5e... as long as all you need to play 5e is dice.

Armor of Agathys 1st level abjuration

Casting Time: 1 action

Range: Self

Components: V, S, M (a cup of water)

Duration: 1 hour

Tags: warlock level1 abjuration

A protective magical force surrounds you, manifesting as a spectral frost that covers you and your gear. You gain 5 temporary hit points for the duration. If a creature hits you with a melee attack while you have these hit points, the creature takes 5 cold damage.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, both the temporary hit points and the cold damage increase by 5 for each slot level above 1st.

You can find more information on this spell in: PHB.215