Reaction Duel – Beat the Green Flash
Reaction Duel is a two-player reflex showdown on one keyboard. The screen stays dark while you wait, then snaps bright green—Player 1 hits F, Player 2 hits J. Whoever reacts first takes the round; press before the flash and you foul, giving the point to your rival. First to three wins the best-of-five.
Updated 2026-08-03 · two-player
About this game
Each wait uses a random delay so you cannot count beats. After a tap you see either FOUL or your reaction time in milliseconds, then the next wait arms. Share one laptop, keep a finger on F or J, and stay still until the whole canvas turns green.
Controls
| Player | Keys |
|---|---|
| Player 1 | F (react) |
| Player 2 | J (react) |
| Both | R = restart · Best of 5 · Early press = foul |
Common use cases
- Settle who has the quicker trigger finger in a short best-of-five.
- Practice holding still through a fake-out wait before the real flash.
- Run a fair F-versus-J duel with no networking or accounts.
Tips
- Rest on your key during the wait, but do not press until the screen goes green.
- Watch the full canvas—the flash fills both halves, not only the GO! text.
FAQ
What happens if I press before the green flash in Reaction Duel?
That is a foul. The other player wins the round even if they have not pressed yet.
How do you win a Reaction Duel match?
It is best of five—first player to three round wins takes the match.
Is Reaction Duel online multiplayer?
No. Both players share one keyboard on the same device.
Can I play Reaction Duel on a phone?
This build expects a desktop or laptop keyboard with F and J.