MenteRush

What it is

A mental arithmetic game against the clock. Numbers appear one at a time, you add them up in your head and type the total before time runs out. Consecutive correct answers build a combo that multiplies the score, across five tiers that change colour, sound and effect intensity. Three mistakes end the run.

Why I built it

MentePro already did this on Android, but installing an app to practise for thirty seconds is too much friction. On the web you open a link and play. The real challenge was never the arithmetic — that is four lines — but making it feel right: a hit should sound, vibrate and show, and a miss should sting.

Decisions

No backend, no database. Everything lives in the browser and records go to localStorage. A game of thirty-second runs does not justify a server, and without one there is nothing to go down and nobody's data to keep.

React as the only runtime dependency. Sound is synthesised with the Web Audio API and the particles are canvas 2D, no libraries. Pulling in an audio or particle engine would have multiplied the weight to do the same thing.

The rules in pure TypeScript. Difficulty, scoring and the run's state machine live in domain/, unaware that React exists. That is why they can be tested without mounting a single component: 67 tests across domain, persistence and UI.