● Free · no signup · ~5 min

Try a system design drill

One focused, interview-style prompt. Write a short answer and an AI interviewer grades it in seconds.

The prompt

Design the data model for a chat app's message storage: 1:1 and group threads, with fast 'recent messages per conversation' reads.

50M DAUReads dominateMessages immutable

Your answerFill in each line — schema, bullets, or prose.

Store ◯·Schema / key fields ◯·Access patterns ◯

No diagram needed for a drill — that's what the full interview is for.