● 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 API for a payments 'create charge' flow that must be safe to retry on network failure.

Exactly-once chargeClient may retryReturn clear error codes

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

Endpoints ◯·Request / response shape ◯·Idempotency / pagination ◯

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