Reaction Time Test
When the screen turns green, click as fast as you can. Five rounds, then your average in milliseconds — and how it stacks up. Spacebar works too.
What you're actually measuring
The number this test gives you is a simple visual reaction time — the gap between a stimulus appearing and your body acting on it. In those few hundred milliseconds a surprising amount happens: light hits your retina, the signal travels to the visual cortex, your brain registers the change and decides to move, a command runs down your spinal cord to the muscles of your hand, and the muscles contract to complete the click. Each stage costs time, and the total is rarely under 200 milliseconds.
For most healthy adults, simple visual reaction time sits around 200–300 ms, clustering near a quarter of a second. Reactions to sound are a little quicker than to light, and touch quicker still, because those signals take more direct neural routes. Anything below roughly 100 ms isn't a reaction at all — it's anticipation, a guess that happened to land. That's exactly why this test counts a click before the green as a false start, and why sprint officials disqualify starts faster than 100 ms.
What moves the number
Reaction time is genuinely trainable at the margins — a few rounds of practice will shave off some milliseconds as you learn the task. Beyond that, it's shaped by alertness, sleep, age, caffeine, and the device you're using. A laggy screen or a high-latency mouse adds its own delay that has nothing to do with your nervous system, so results vary between setups. Fatigue and distraction slow you down measurably; this is part of why drowsy driving is so dangerous.
A fair-comparison caveat
Treat your score as a fun, rough benchmark, not a medical or cognitive assessment. Display refresh rate, input lag, and even browser load all add noise on the order of tens of milliseconds. To compare yourself meaningfully, compare runs on the same device, well-rested versus tired, or before and after coffee — not your laptop against a friend's phone. If you're ever concerned about genuine changes in your reflexes or coordination, that's a question for a clinician, not a web toy.
Privacy
Everything runs in your browser. No scores are uploaded or stored — refresh the page and it's gone.