It draws a keyboard and lights each key as you press it, so you can walk across the board and see at a glance which keys work and which never registered. Behind the map it records what a hardware test needs: how many times each key was pressed, the most keys held at once (rollover), the auto-repeat delay and rate when you hold a key, keys that are held suspiciously long (possibly stuck) and keys that register twice for one press (chatter). Each press also shows the browser's view of it: event.key (the character), event.code (the physical key) and the location (left, right, numpad).
Nothing is recorded outside the page and nothing is sent anywhere; the test lives in memory until you press Reset or leave.
How to test a keyboard
- Press Start test. Focus moves to the map, and browser shortcuts such as Space-to-scroll are paused there so every key can be pressed safely.
- Press every key once, row by row. Each one turns from plain to outlined with a small press counter. The heading counts how many of the 104 (or 87, or 61) keys you have covered; the Keys not pressed yet list names the rest.
- For rollover, hold several keys together, for example A S D F and then J K L ;. The panel shows the highest number held at once and how many of those were ordinary keys rather than Shift, Ctrl, Alt or Meta.
- For repeat, hold one letter for two seconds. The tool measures the delay before the first repeat and the repeat rate in characters per second. These are set by your operating system, so they tell you about your settings rather than the hardware.
- Watch Held now: a key still listed after five seconds without your finger on it is physically stuck or shorted. Double presses lists keys that came back down within 30 ms of being released, the signature of a worn switch.
Tab and Escape are never blocked: Tab still moves focus out of the test, and Stop test ends it.
Rollover, ghosting and blocking
A keyboard reads its keys through a grid (matrix) of wires. With three keys pressed at the corners of a rectangle on that grid, a cheap keyboard without diodes may see the fourth corner as pressed too: that phantom press is ghosting. Most keyboards avoid it by blocking: they ignore the extra key, so it simply does not appear. In this test, ghosting shows up as a key you did not touch lighting up; blocking shows up as a key that stays dark while you hold others.
Rollover is how many keys register at once. A keyboard that speaks the USB boot protocol reports at most six ordinary keys plus the modifiers, which is why "6KRO" is common; gaming and mechanical boards often claim N-key rollover (NKRO). Office keyboards may only guarantee two or three keys in some combinations. Hold different groups: rollover is often better on WASD than elsewhere because manufacturers wire those keys with gaming in mind.
Layouts, languages and what the browser cannot see
The map is a US ANSI board and keys are matched by event.code, the physical position, not by the character. That makes the test correct whatever language you type in: with Vietnamese Telex or VNI, with AZERTY or Dvorak, the A position is still KeyA. ISO keyboards (common in Europe and the UK) have an extra key next to the left Shift, reported as IntlBackslash, and an L-shaped Enter; JIS keyboards add keys such as IntlYen, IntlRo, Lang1 and Lang2. Those extras are listed under the map when you press them. If your board is tenkeyless or compact, switch the layout so the counts match.
Some keys can never be tested in a browser: Fn is handled inside the keyboard, many media keys and the power key are taken by the operating system, and shortcuts such as Ctrl+W, Alt+F4 or the Windows key may act before the page sees them. On macOS, the browser receives no key-up for other keys while Command is held, so the tool releases them when Command is released. If you switch windows mid-test, held keys are cleared, because the browser stops reporting releases. For the raw event fields of a single key, the key code viewer shows everything the browser reports.
Reading the results
- All keys outlined, rollover of 6 or more, no chatter: the keyboard is healthy.
- A key never lights up: try it in another app; if it fails there too, it is the switch, the membrane or the matrix.
- A key lights up by itself or stays held: liquid damage, a stuck keycap or a short. Unplug the keyboard before cleaning.
- Chatter on one key: common on worn mechanical switches; compressed air, a switch swap, or a debounce setting in the keyboard's software can help.
More on interpreting rollover, ghosting and chatter, with combinations to try, is in how to test a keyboard for ghosting and rollover.
