You summon a devil from the Nine Hells. You choose the devil's type, which must be one of challenge rating 6 or lower. The devil appears in an unoccupied space that you can see within range. The devil disappears when it drops to 0 HP or when the spell ends. Roll initiative for the devil, which has its own turns. It is under the DM's control and acts according to its nature, which might result in its attacking you, or trying to tempt you to undertake an evil act in exchange for limited service. The DM has the creature's stats. On each turn, you can try to issue a command (no action required). You must make a Cha (Deception, Intimidation, Persuasion) check versus its Wis (Insight) check. If failed, it's immune to your commands. If successful, the devil carries out your command. If your concentration ends before the spell reaches full duration and it is immune to your commands, it disappears. Instead, it acts in whatever manner it chooses for 3d6 minutes, then it disappears. See PHB for expanded details.
When you cast this spell using a spell slot of 6th level or higher, the challenge rating increases by 1 for each slot level above 5th.
a ruby worth at least 999gp