The clue to “all ready” is the word “all” meaning “everyone.” (Everyone is ready.)
The single word “already” refers to something accomplished in the past.
- Are they all ready?
- (Is everyone ready?)
- They left already.
- (They aren’t here anymore.)
- The turkey is cooked, the dressing is baked, the potatoes are mashed, and the salad is tossed. I think it’s all ready. Come and get it!
- (All the food is prepared.)
- Did you bake the pie already?
- (Has the pie been cooked?)