Keyboard Tester

Three things it checks

1. Dead keys. Type across the whole board. A key that never turns green is either broken or sending a code the browser doesn't expose. The line under the diagram shows the raw key and code for the last press, so a key that is missing from the picture still shows up there.
2. Ghosting. Hold down as many keys as you can with both hands. "Max at once" is the largest number the keyboard reported pressed simultaneously. Cheap membrane boards stall at 2 to 6 depending on the combination; boards advertised as N-key rollover should take everything you can reach.
3. Chatter. A worn switch releases and re-presses itself within a few milliseconds, so one keystroke types two letters. If a key registers again less than 30 ms after it was released, it counts as chatter and the key is outlined in red. Type normally for a minute; a healthy keyboard shows zero.

Keys that behave differently

• Browser shortcuts are blocked while this page has focus, so Ctrl+W, F5 and friends just light up. The Windows or Cmd key still opens its menu on some systems; that's the operating system, not the page.
• Print Screen, media keys and Fn are handled below the browser and usually never arrive.
• Laptop keyboards without a number pad and ISO layouts with the tall Enter are drawn as the common US layout; a key that isn't on the drawing still registers and is reported under it.
• On a phone the on-screen keyboard sends a generic code for most keys, so the diagram is of little use there.

Other tests