Input device tests — keyboard, mouse, controller and touch

Keyboards: dead keys, ghosting and rollover

The keyboard check lights up each key as it registers, which makes a genuinely dead key obvious in seconds. Press every one, including the modifiers and the number pad, and look for the ones that never light.

Rollover is the subtler thing to test. Hold several keys at once and watch how many the board reports simultaneously. Cheap membrane keyboards commonly stop at two or three in a given cluster and silently drop the rest — that is ghosting, and it matters if you game or type fast. Mechanical boards advertising NKRO should keep counting well past six.

One caveat worth knowing: browsers cannot intercept a few system shortcuts. Alt+Tab, Cmd+Tab and the Windows key are handled by the OS before the page ever sees them, so a blank result there is expected rather than a fault.

Mice: buttons, wheel, double-click and polling rate

Buttons and scroll direction are quick to confirm. The interesting failure is double-click chatter, where a worn switch bounces and sends two clicks when you meant one — dragging a file suddenly opens it, or a single click selects a whole word. Repeated clicks with unnaturally short gaps between them are the signature, and it is a hardware fault that cleaning rarely fixes.

Polling rate is a separate measurement, reported in Hz. It tells you how often the mouse reports its position: 125 Hz is the plain USB default, gaming mice run 500 Hz or 1000 Hz, and newer wireless models reach 8000 Hz. Browsers can only measure what the OS hands them, so treat the number as a solid sanity check rather than a lab result.

Controllers and touchscreens

For gamepads, the thing to look for is stick drift — a stick reporting movement while you are not touching it. Small values that sit still are usually harmless deadzone noise; values that wander on their own are a worn potentiometer, and that is what makes a character walk off on its own.

Touchscreen problems are usually regional. Trace slowly across the whole surface and watch for a band or corner where the line breaks up. Multi-touch is worth checking too, since a panel can register one finger perfectly and lose the second.