Design Slack / Chat / Messaging Platform

System DesignDatabricksLast reported July 2026High Frequency
Reported
15× across candidate reports
First seen
February 2025
Last reported
July 2026
Reported outcome
mixed

Problem Overview

Design a Slack-like chat/messaging platform. The system should support: 1. One-to-one and group messaging (channels/threads) 2. Users subscribing to multiple channels; messages broadcast to all subscribers 3. Message deletion — including deletion from both online and offline users (a consistently probed deep-dive area) 4. Concurrent operations: e.g., send message while…

  • 7 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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