The four tests

reaction — wait for green, click. Five rounds, averaged. Skilled gamers land around 150–180 ms; the average adult sits near 250 ms. Your monitor and input chain add 10–50 ms on top, so compare runs on the same machine.
aim — pop 20 targets as fast as you can. Reports milliseconds per target and accuracy (stray clicks count against you).
memory — a number flashes, you type it back, it grows one digit per level. Most people hold 7±2 digits; double digits is rarefied air.
typing — 15 seconds of lowercase dev words. Space submits a word; only exact matches count toward WPM (the standard 5-characters-per-word formula).

Tips for honest numbers

Close background tabs (a busy main thread inflates reaction times), use a mouse rather than a trackpad for the aim trainer, and do a warm-up run of each test before recording your real attempt. High-refresh monitors genuinely help — a 60 Hz panel adds up to 16 ms of display lag per frame.

Privacy

No camera, no microphone, no account. Personal bests are stored in localStorage on your device and never leave it. Open DevTools → Network and watch nothing happen.