The screen will turn green — wait for it to switch to red, then click as fast as you can. The delay is random (5–15 seconds) so you cannot anticipate it. Your score is measured in milliseconds from red to click.
The Reaction Time Test measures simple visual reaction time — the delay between a visual stimulus (the screen turning red) and a voluntary motor response (clicking or tapping). This is one of the most studied metrics in cognitive psychology and sports science. A green waiting phase with a random 5–15 second duration prevents any form of anticipation: you cannot guess when red will appear, so you must react to the stimulus itself rather than prepare for a fixed moment.
Average human simple reaction time to a visual stimulus is approximately 200–250 milliseconds. Athletes and esports professionals often reach 150–180 ms after training. Times below 150 ms are rare in uncontrolled browser environments due to display latency, input polling rates, and JavaScript scheduling overhead — results this fast likely include some hardware measurement noise. After the test, enter a nickname of up to 8 alphanumeric characters to save your score to the global leaderboard. Lower is better.