Press every key and see it light up — find keys that don’t work, stick or register the wrong key.
Check a new keyboard or find out which key is playing up. Click the test area and press keys — each one lights up while held and turns green once it has registered, so dead keys are easy to spot.
The name and code of the last key appear above, which also helps when a key types the wrong character because the keyboard layout is set wrongly.
Usually not: the keyboard layout or language in your computer’s settings doesn’t match the keyboard. Check the input language (for example English US vs UK).
Some keys, like Fn or media keys, are handled by the keyboard itself and never reach the browser. Others, like Print Screen, may be taken by your operating system.