Design
Real-Time Collaborative Code Editor
Design a browser-based collaborative code editor (like this app's own canvas, but for code) supporting multi-cursor editing and live execution.
This is a Low-Level Design (LLD) problem. New to LLD vs HLD? Start here.
01 - Why interviewers ask this
It combines the Google-Docs collaborative-editing problem with sandboxed code execution — interviewers check if you isolate untrusted execution as rigorously as you handle concurrent edits.
02 - Where this system exists in the real world
You interact with this design every day.
Replit / CodeSandbox collaborative coding platforms
Technical interview live-coding platforms
Pair-programming and classroom coding tools
03 - What you'll master
Solve this once. Know it forever.
Apply CRDT/OT concepts to a code editor
Sandbox untrusted code execution safely
Stream execution output to multiple viewers live
04 - What you'll design
6 functional · 3 non-functional requirements.
Multiple users edit the same code file concurrently with live sync
5 more requirements inside
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05 - Companies that ask this
You may face this exact question in your next interview.
Ready?
Open the canvas.
Design it yourself.
See all requirements, use staged hints, run your code, and compare with community discussions - all on the same canvas.