Mock design round with a checklist
45 min · Advanced
A design round is a 45-minute interview where you design a system aloud while the interviewer asks questions. The candidates who do well are rarely the ones who know the most tools; they follow a clear order, say their numbers and trade-offs, and stay on time.
Topics in this lesson
- The full checklist: eight steps
- Worked mock round: an online ticket waiting queue
- Handling hints and changing requirements
- A self-scoring rubric for a design answer
- Time checkpoints across a 45-minute round
Key points
- Use the same 8 steps every time: requirements, estimates, API, data, architecture, deep dive, bottlenecks, wrap-up.
- Let the numbers drive the design, and say each step aloud as you start it.
- Welcome hints; for a changed requirement, restate it, change one part, name the trade-off.
- Score yourself with a rubric and keep to time checkpoints: data model by 17, deep dive by 35.
Interview questions this lesson answers
- How do you approach a system design question?
- Why do you spend time on estimates?
- How do you handle a hint from the interviewer?
- The interviewer changes a requirement halfway. What do you do?
- How do you make sure you finish on time?
- How do you practise system design on your own?
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