Conjure Greater Dragon

You summon a dragon of CR ≤ 6, which appears in an empty space you see in range. The dragon disappears when it drops to 0 or when the spell ends. The dragon is friendly to you and your allies for the duration. Roll for its own initiative, and it acts on its own turn. It obeys your verbal commands (free action) if they don't violate its alignment. The DM uses his discretion to decide what's allowed. If you don't issue any commands, it acts according to its own values and alignment (DM's discretion).

If your concentration breaks, the dragon won't disappear. Instead, you lose control over it, and it no longer sees you as an ally but won't necessarily target you but instead acts of its own volition. An uncontrolled dragon can only be dismissed by Dispel Magic or Wish cast at a high enough level and disappears after the duration ends. If you're kind, you'll have the dragon's stats, but your DM can use them too.

At Higher Levels. When cast using a slot of 6th or higher, the CR increases by 1 for each slot above 5th.