A cognitive-ability and reaction-time testing app that doubles as a playground for real-time collaboration. The interesting engineering isn't the tests — it's the self-hosted collaborative document layer underneath them.
The problem
Reaction-time measurement is unforgiving about latency and jitter: a few dropped frames and the numbers are meaningless. Layering collaborative editing on top, where multiple people touch the same document, multiplies the correctness surface.
What I built
- A Tiptap editor wired to a self-hosted HocusPocus backend for conflict-free collaborative editing.
- A reaction-time harness that measures input latency against a high-resolution clock rather than frame ticks.
- A Next.js front end with careful attention to perceived performance.
Outcome
A single codebase that exercised both ends of my range — the product sense to design a testing flow people actually finish, and the frontend depth to make real-time editing feel instant.