How the interviewer opens it
“Design an online examination platform that delivers timed exams, saves answers, and grades submissions. Many candidates start together. The platform must preserve acknowledged saves and prevent duplicate submissions.”
The prompt is vague on purpose. The first minutes are for you. Reduce the prompt to the core features and agree on the numbers before you draw.
What to clarify first
- Exam format and scale
- Exam time
- Traffic and read:write mix
- Latency
- Consistency and availability
- Durability and payload size
- Submission and deadline rules
- Grade rules and results
- Retention and deployment
- External systems and exclusions
The interviewer has the answers. In a SysRound round, Alex gives these answers, as a real interviewer does.
Scope of a strong answer
Core requirements
- Deliver an exam with a common start time and deadline
- Save answers and restore accepted answers after a reconnect
- Accept one final submission per attempt without losing accepted answers
- Grade final submissions and return results
Usually out of scope
- Video supervision and cheat detection
- Question author tools
- Payments
- Essay assessment and execution of candidate code
- Service continuity after a complete region failure
What interviewers ask about
- Exam access and time
- Candidates arrive together, but slow access must not change the common deadline. The service must also prevent early question access.
- Answer saves and retries
- A timeout hides whether the service saved an answer. Delayed requests and multiple tabs can replace newer answers with older answers.
- Submission at the deadline
- Answer saves, explicit submissions, and the deadline can race. The service must freeze one answer set and return one final receipt.
- Grade completion
- Many attempts become final together. Failures can leave grades absent or repeated unless the service can recover each final submission.
Common mistakes
- The server trusts a client timer to enforce the exam deadline.
- The client treats a failed network response as proof that the service rejected the save.
- The server allows delayed saves to overwrite newer answers.
- The design treats a disabled Submit button as protection against duplicate submissions.
- The service grades answers before it freezes their final revision.
- The capacity plan covers average traffic but ignores simultaneous starts and deadline submissions.
The bar by level
- Senior (L5/E5)
- The candidate defines revision conflicts and durable receipts. The design resolves races among saves, submissions, and deadlines. The candidate sizes burst capacity and explains reliable grade recovery.
- Staff (L6+/E6+)
- The candidate defines acceptance boundaries, clock assumptions, and partition ownership. The candidate tests zone failure and deadline overload. The design supports recovery and evidence for disputed grades.
Sources · 1 reference
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SysRound · 1 record
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Design an online examination platform
Reported date not specified
Source snapshot: Nov 12, 2026
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