Todo List / Collaborative To-Do System Design

Also reported as Shared To-Do List System Design · Collaborative To-Do List · Design a Shareable Concurrent Todo List

System DesignRobloxLast reported April 2026Medium Frequency

Reported: 6× across candidate reports
First seen: February 2025
Last reported: April 2026
Reported outcome: mixed

Problem Overview

Design a collaborative to-do list application. Users should be able to create to-do lists and individual tasks, share lists with other users, and concurrently edit the same list in real time. The system must handle multi-user synchronization, real-time update notifications, and read/write conflict resolution…

5 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.