How to run a design interview

System Design · lesson 1 of 32 · 3 min read

Know the order to attack a design question in, and what the interviewer is actually grading.

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Key points

  • Do not start drawing. Spend the first five minutes on what the system must do, who uses it, and how many of them there are.
  • A workable 45-minute budget: 5 min requirements, 5 min estimates, 10 min high-level boxes, 20 min deep dive, 5 min bottlenecks.
  • Order of attack: features → scale numbers → API → data model → boxes → deep dive on the one hard part.
  • Say the trade-off out loud: I pick X because Y, and the cost is Z. Reasoning is graded, not the “right” answer.
  • Ask before assuming. Whether counts must be exact or can be approximate changes the whole design.
  • There is no perfect design. There is a design whose weaknesses you can name before the interviewer does.

Drive the conversation: clarify, estimate, then design - in that order.

Requirements and napkin math

This is a reading copy. The full lesson — with the visual explainer, the interactive lab and a Run button for the code — lives in the System Design course, and every lesson in it is listed on the System Design contents page.