Detect Aura (5e Spell)
From D&D Wiki
|Casting time:||1 action|
|Duration:||Concentration, up to 1 minute|
For the duration, you can visibly see the strength of any creature you can see within 60 feet of you. The strength of the creature's aura depends on the CR of the creature, and can be very strong (for CR 17 or above), strong (CR between 16 - 11), medium (CR 10 - 5), average (CR 4 - 1) or weak (CR 1/2 or lower). The stronger the creature, the brighter and larger the aura.
In addition, the color of the aura also can reveal another aspect of the creature's power. A creature with 20 or more hit dices have a red aura; a creature with hit dices ranging between 19 and 10 have a orange aura aura; a creature with 9 hit dices or lower have a yellow aura.