What these tests are for
Most tests on this site check a device: a screen, a speaker, a mouse. The tests in this section check the person in front of it, using the device as the measuring instrument. They run in the browser with no install and no account, and nothing you do is uploaded.
The reaction time test is the first of them. The screen stays dark for a random moment and then lights up; you tap, click or press Space as fast as you can. After 3, 5 or 10 attempts you get your average in milliseconds, your fastest and slowest attempt and the number of false starts. Presses before the light, or impossibly fast ones, do not count, so guessing does not help.
How to get a result you can trust
A human test is only as good as the conditions it runs in. Sit comfortably with the whole screen in view, keep a finger ready on the button or the screen and look at the centre. Avoid a Bluetooth mouse or keyboard if you can, and close heavy tabs and video calls that make the browser late to draw frames. Warm up with a round or two: the first attempts are nearly always the slowest.
Your own state matters as much as the setup. Tiredness, a late evening, caffeine, alcohol and simple boredom all move reaction time by tens of milliseconds. One result is a snapshot. Several results at the same time of day, on the same device, show a trend.
How to read the numbers
Reaction time in a simple visual test is usually between 200 and 300 ms for adults. It gets a little slower with age, and it improves with practice only up to a point: the first days of training bring the biggest gain, after that the numbers flatten. A result far outside the usual range is more often about the device than about you. Before drawing conclusions, check the screen with the refresh rate test in the Display section and the mouse with the mouse test in the Keyboard & mouse section.
Frequently asked questions
Do these tests measure me or my device?
Both, and it is worth knowing where the line is. The reaction time test measures the whole chain from the light on the screen to the press arriving in the browser. Your eyes, brain and hand are the biggest part of that time, but the screen, the input device and the browser add a few to a few dozen milliseconds on top. Compare your results on the same device to see changes in yourself.
Can I compare my result with a friend's?
Roughly, if you both use similar devices. A friend on a 144 Hz monitor with a wired mouse starts with an advantage of a few dozen milliseconds over someone on a phone. For a fair duel, take turns on the same computer or phone.
Why is there no online leaderboard?
Everything runs on your device and nothing is sent to a server, so there is nothing to rank. Your best result is kept only in this browser. A leaderboard would need your results on a server and a way to catch cheating, and neither fits a site that promises not to upload anything today.