Keyboard tester

The test reports event.code, which is the physical key position, rather than event.key, which is the character it produces. That distinction matters: on an AZERTY or Dvorak layout the key where QWERTY has Q still reports KeyQ, because the code describes where your finger is and the key describes what the operating system decided that means. If a key produces the wrong character, the keyboard is fine and the layout is wrong — a software fix, not a hardware one.

A few keys will never light up and that is not a fault. Fn is handled by the keyboard controller and usually never reaches the operating system at all. Media and brightness keys are often intercepted the same way. Certain combinations are claimed by the operating system before any browser sees them — Cmd+Tab, Alt+Tab, Ctrl+Alt+Delete — so those cannot be tested from a web page by anyone.

While the test runs it swallows key presses so the page does not scroll, tab away or open a find bar mid-test. Stop the test to get normal shortcuts back. One thing worth trying deliberately: hold three or four keys at once. Cheap membrane keyboards drop the third or fourth simultaneous key — ghosting — and the held-down count is how you see it.