Press any key and watch it light up. Find dead or stuck keys, check rollover, and see key codes — perfect before buying a used keyboard or diagnosing one.
⌨️ Key presses only light up the on-screen keys — nothing is logged or uploaded.
Checking a second-hand or refurbished keyboard? Run through every key in under a minute and spot the dead ones before you pay.
One key acting up? Confirm whether it's the hardware (never lights up) or software, and see if a key is stuck firing on its own.
Press W+A+Shift+Space together — if all light up, your keyboard handles game key combos. If not, it has anti-ghosting limits.
The tester reports the key events your browser receives, which makes it useful for confirming whether a key registers at all, whether it repeats when held, and whether it produces the character you expect. A key that produces nothing here is failing before the browser, which points at hardware, the connection, or the operating system's key mapping.
It also distinguishes physical position from produced character. Browsers report both a code, identifying the physical key by its position on a standard layout, and a key, giving the character that position produces under the current layout. A keyboard typing the wrong letters usually has a layout mismatch rather than a fault — the classic case being a QWERTY keyboard set to AZERTY or Dvorak in software.
Sticky or intermittent keys often show as a key that requires more force or registers inconsistently. Debris under a keycap is the usual cause on membrane and scissor-switch keyboards, and compressed air or careful keycap removal resolves most of it.
On cheaper keyboards, certain combinations of three or more simultaneous keys fail to register, and this is a design consequence rather than a defect. Keys are wired in a matrix of rows and columns to reduce the number of connections, and without isolation diodes the controller cannot distinguish some multi-key patterns — it either misses a key or reports one that was not pressed, which is the phenomenon called ghosting.
Manufacturers work around it by blocking ambiguous combinations, which is why a key sometimes simply does nothing while two others are held. Most keyboards guarantee two-key rollover plus common modifier combinations, which covers ordinary typing.
N-key rollover, where every key is independently detected, requires a diode per key and is found on better mechanical keyboards. It matters for gaming and for fast typists, whose keypresses overlap more than they realise. Testing your own combinations here shows what your keyboard actually supports, and note that some USB implementations limit simultaneous keys at the protocol level even where the hardware supports more.
Some keys will not appear no matter how well the keyboard works, because the browser never receives them. The operating system intercepts certain combinations first — Alt+Tab, the Windows or Command key alone, Ctrl+Alt+Delete on Windows — and hardware-level media, brightness and volume keys are frequently handled by firmware without generating a standard key event.
Browsers also reserve combinations for themselves, so Ctrl+W, Ctrl+T and function keys such as F5 and F12 may act on the browser rather than reaching the page. A key not appearing here is therefore not proof it is broken.
Fn key combinations are the clearest example: on most laptops the Fn key is handled entirely within the keyboard controller, producing a different key code rather than an event of its own, so the Fn key itself is invisible to software. If a key works elsewhere but not here, interception rather than failure is the likely explanation. Nothing typed here leaves your browser, which makes the test safe to use with any key.
Almost certainly, if every other key works here. Try a different USB port or cable first to rule out a loose connection, then test again.
A few keys are intercepted by the operating system or browser (like media keys, Fn, or some Windows shortcuts) and never reach the page. That's expected, not a fault.
Yes — it works with any keyboard the browser can see, including laptop and external ones.
Keyboard matrix limitations. Without a diode per key, the controller cannot resolve some three-key combinations, so it blocks them — this is ghosting. N-key rollover keyboards avoid it with a diode per key.
The browser never receives them. Fn is handled inside the keyboard controller, and the operating system intercepts keys like Alt+Tab and Ctrl+Alt+Delete before any page sees them.