System Design: Online Chess Game

System DesignOpenAILast reported August 2026High Frequency
Reported
19× across candidate reports
First seen
January 2026
Last reported
August 2026
Reported outcome
mixed

Problem Overview

Design a real-time online chess platform similar to chess.com. The system must support: (1) player matchmaking based on skill level (ELO rating); (2) real-time gameplay with bidirectional move synchronization between two players; (3) per-player countdown timer — each player has a limited pool of thinking time, requiring a server-authoritative countdown;…

  • 11 candidate-reported follow-ups — the exact probes interviewers asked, with the trigger for each
  • The rest of the problem statement — full requirements, constraints, and edge cases
  • Approach and trade-offs — what passing candidates did, and the mistakes that sink people
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Verified Source
Every question is reconstructed from multiple independent candidate reports. Verbatim follow-ups, not invented ones.
Codex Fact-Checked
Technical claims, formulas, and scale numbers are reviewed against primary sources.
Interviewer Follow-ups
The exact follow-ups reported by candidates, with the trigger that prompts each one — plus the mistakes that sink people.
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