When you start, the box turns red and waits for a random delay of between one and a half and four and a half seconds. The moment it turns green, the page records a timestamp using your browser’s high-resolution timer. When you tap, click or press the space bar, it records a second timestamp, and the difference between the two is your reaction time in milliseconds. After five rounds the tool shows your average and keeps your single best time on this device (it is stored only in your browser, never sent to us).
The random delay matters. If the green appeared after a fixed pause, you would learn the rhythm and start moving before you actually saw the colour change. Tapping while the box is still red counts as a false start: that round is thrown away and you simply try it again.
For a simple “see a change, press a button” task like this, many adults land somewhere around 200–300 ms on a computer. Your number includes more than your brain, though. The screen’s refresh rate, the browser, a wireless mouse or Bluetooth keyboard, and the touch sampling of a phone can each add a few to a few dozen milliseconds. That is why it is best to compare results from the same device rather than against a friend on a different phone.
No. It is a fun browser tool. It cannot diagnose anything, and results from a web page are affected by hardware delays you cannot see.
Touch screens scan for touches a set number of times per second, and some phones also add a small delay before they report a tap. A wired mouse on a high-refresh monitor usually gives the lowest numbers.
A little. Warming up and learning to relax before the change usually shaves off some time. Beyond that, the gains are small. Fast-paced games are a fun way to keep your reflexes sharp. Try one from our quick 5-minute games.
Only your best time, and only in your own browser’s local storage. Clearing your browser data removes it.