About Keyboard Tester
Check that every key on your keyboard works. Click Start test, then press each key: a pressed key lights up while you hold it and turns green once it has been registered, so at a glance you can see which keys you have tested and which ones are still missing. A counter shows how many keys you have tested, and a list names the keys you have not pressed yet.
The tester also helps you spot ghosting. It shows how many keys you are holding right now and the highest number you have held at once, so you can press several keys together and see whether all of them register. Note that many keyboards limit simultaneous keys by design, and cheap membrane boards often drop keys when three or more are pressed in certain combinations.
For each key press you can read its name, its code (the physical key position, such as KeyA or Numpad5), its legacy keyCode and its location (left, right or numpad). That is useful for developers and for anyone choosing keyboard shortcuts for games or software. Pick the full layout with a numpad or the compact layout without one.
Everything runs in your browser and no keystrokes are sent anywhere. While the test is running, the page stops the browser from reacting to keys such as Tab, F5 or Alt so they can be tested, which is why you finish with the Stop test button.
Limits to know: this checks the standard US (ANSI) layout shown on screen, so keys on other layouts may appear as extra keys. Some keys cannot be seen by any web page: the Fn key, most media and brightness keys, and on some systems the Windows key or PrintScreen. A key that does not light up here but works elsewhere is usually one of those.