What to work through
Work through a collaborative document editor as a spoken system design interview. Start by clarifying the scope, sketch a working design and explain the trade-offs behind your choices.
- Open a document and edit its text with several other people at the same time
- See other people's edits appear as they type
- See where each other person's cursor and selection are, with their name
- Keep typing through a dropped connection and have the work saved when it returns
- Undo and redo your own edits
Constraints to discuss
- Your own keystroke shows within 200 milliseconds, whatever the connection
- Everyone ends with the same document once edits stop
- No edit is lost, whether made at the same moment as another or during a dropped connection
- Up to 100 people can have a document open at once
Need a starting point?
Watch for these common gaps as you prepare:
- Forgetting that a selection must survive edits made by others
- Saving presence with the document
- Treating it as a backend question and leaving the editor out
- Undo that reverses another person's edit
- Blocking typing while the connection is down
Why this question is in the collection
These sources connect the problem to company interview reports or preparation guides. They do not guarantee what a company will ask you.
- Meta: A full-stack software engineer's own post about an onsite, November 2025: one question was to build a collaborative document editor, discussed as its architecture, how edits are transformed, and conflict resolution.
- Adobe: A senior computer scientist candidate in Bengaluru, May 2026: the second round, meant to cover frontend, became a design of a real-time collaborative text editor, then shifted toward a collaborative drawing tool.
- Accolite: A senior frontend engineer (SDE 2) reports a system design round in October 2025: a collaborative note-taking web app like Notion, with syncing between clients, offline editing and conflict resolution. The post is titled for Accolite but also tagged LinkedIn, and its one reply, unanswered, asks which company asked it.
- Tencent: A frontend new graduate reports a technical phone screen from late 2025 on designing a docs system with real-time collaboration, concurrent edits and its architecture; the details sit behind a login.