Collaborative whiteboard

Multiple people draw on a shared canvas in real time, with undo and offline tolerance.

Why build it

Conflict resolution is the hard part. Building it on a CRDT or operational model teaches distributed-state ideas you can discuss in interviews.

Features

• Shared canvas with shapes and freehand
• Live cursors
• Per-user undo
• Reconnect without losing edits
• Board persistence

Roadmap

1. p1

   Single-user canvas

   • Canvas rendering loop with hit testing
   • Shape model and selection
   • Local undo stack
2. p2

   Sync model

   • Choose CRDT (Yjs or Automerge) or build last-writer-wins and compare
   • Server relay over WebSockets
   • Cursor presence
3. p3

   Resilience

   • Offline edits merge on reconnect
   • Snapshot and compaction
   • Fuzz test with random concurrent edits
4. p4

   Scale and ship

   • Load test 50 users per board
   • Persist to object storage or Postgres
   • Write an architecture doc

Common pitfalls

• Syncing whole-document state on every change
• Sharing one undo stack across users

Skills you will practise

• CRDTs
• WebSockets
• Canvas
• Fuzz testing