How to test your keyboard for stuck keys

Typing in a document shows the final result, not the key state. A stuck modifier might change a shortcut without producing a visible character. A key that repeats quickly can look like a software bug. A tester shows which keys the browser is receiving and when they are released, which makes those problems easier to see.

The type-type keyboard tester highlights every key you press. It covers letters, numbers, punctuation, modifiers, function keys, arrows and the optional numpad and navigation sections. It needs a physical keyboard and a screen at least 768px wide, so use a desktop or laptop rather than a phone.

Close any app that captures keyboard shortcuts, such as a game, a remote desktop client or a macro tool. Make sure the browser window has focus. If you are testing a wireless keyboard, check the battery first; a low battery can cause missed or repeated keys that look like a hardware fault.

Decide what you are testing. If you suspect one key, test that key first and then its neighbours. If the whole keyboard is unreliable, work through the rows in order. Keep a note of every key that fails so you can describe the pattern later.

Do not press several keys at once during the first pass. Press one key, release it, and watch the result. Combination tests come later, after you know which individual keys work.

Open the tester and press each key once. The matching key on the board should light up while it is held and return to its normal state when you release it. The tested counter should increase for each new key. If a key stays lit, note it as stuck. If it never lights, note it as missing.

Test the modifiers separately. Hold Shift and press a letter, then release both. Do the same for Ctrl, Alt and Meta. A modifier that stays active can make the next key behave incorrectly even though the modifier itself looked fine at first.

Use the reset button between passes if you want a clean count. Test the function row, arrows and numpad only if your keyboard has them; compact keyboards may not. Enable the optional sections in the tester before pressing those keys.

A key that lights up and clears normally is working. A key that stays active after release is stuck or the browser missed the keyup. A key that never appears may be handled by the operating system, or it may be dead. Test it in a plain text field and, if possible, on another computer.

If several keys fail together, look for a pattern. Keys in the same row may share a connection. Keys that fail only when pressed together may be hitting a rollover limit. A keyboard that reports every key individually is said to have n-key rollover; a cheaper keyboard may stop registering some combinations.

A key that types two characters from one press is usually bouncing or repeating. Try another USB port and check the operating system's key-repeat settings. If the behaviour continues, the switch may be worn.

Test the keyboard on another computer if you can. If it fails there too, the keyboard is the likely cause. If it works elsewhere, check the original computer's USB port, cable, driver and accessibility settings. For a wireless keyboard, replace the battery and re-pair it before assuming the keys are broken.

Try a different app and a different browser. A page that captures keys, such as a game or a remote desktop session, can make a working keyboard appear broken. Close those apps and test again in a simple text field.

Turn off and unplug the keyboard before cleaning. Use compressed air and a soft brush to remove dust. For a mechanical keyboard, remove the keycap over a suspect key and check for debris. Do not spray liquid cleaner into the keyboard.

Retest the same keys after cleaning. If the problem is gone, keep a note of what caused it and clean the keyboard regularly. If the key still sticks, inspect the switch or membrane. A mechanical switch may be replaceable; a membrane keyboard usually is not.

If the keyboard is under warranty, contact the seller before opening the case. If it is not, compare the cost of repair with the cost of a replacement. Keep the old keyboard until the new one works in the same ports and apps.