Bring a large pot of lightly salted water to a boil. Cook macaroni in the boiling water, stirring occasionally until cooked through but firm to the bite, about 8 minutes. Drain.
Rinse macaroni in cold water until cool; drain.
Stir mayonnaise, onion, parsley, mustard, rice vinegar, sugar, celery seed, and salt together in a bowl. Add macaroni and eggs and stir to coat.
Chill in the refrigerator for 30 minutes before serving.