How to Check a Keyboard, Mouse and Monitor

Test early, while you can still return it

Shops usually accept returns only for a short period after delivery, and second-hand sellers often not at all once you have left. So the time to test is the day the device arrives or the moment you meet a seller, not when a fault finally annoys you. A browser test page is handy for this: it needs no installation, works on any computer you are handed, and shows exactly what the device sends.

One limit applies to every test below: a browser sees only what the operating system passes on. A key remapped by vendor software, a mouse button bound to a macro or a display scaled by the system will look different in a browser than on the hardware label, so when something seems wrong, check the settings before blaming the device.

Keyboard: every key, then combinations

Start by pressing every key once and watching each one register. Any key that never lights up is either dead or swallowed before it reaches the browser: Fn, some media keys and laptop brightness keys are handled by the keyboard or the system and never appear, which is normal. Then type a sentence slowly in a text box and look for doubled letters. A switch that registers one press twice, called chatter, is a common fault in worn mechanical keyboards and usually gets worse over time.

For games, test combinations. Hold the keys you would hold together, such as W, A and Shift with Space, and see whether every one still registers. If one does not, the keyboard is blocking that combination (ghosting). Budget and laptop keyboards share wiring between keys and block some three-key combinations; a keyboard on the USB boot protocol reports at most six ordinary keys at once, while n-key rollover models should register every key you can reach.

Mouse: buttons, wheel and double clicks

Press each button separately, including the middle click and the side back and forward buttons, and roll the wheel both ways. A wheel that occasionally jumps in the wrong direction has a worn or dirty encoder. The most common mouse fault, though, is a main button that sometimes registers a single press as two clicks: files open when you meant to select them, and drags drop early. Press the button slowly twenty or thirty times and check that the count goes up by exactly one each time.

A click-speed test (clicks per second) is mostly for fun or for games, where 6 to 7 is typical. It is also a quick way to feel whether a button's travel is even. If a high-end mouse feels sluggish, check its polling rate and DPI in the vendor software rather than in a browser, which cannot measure either reliably.

Monitor: pixels, backlight and refresh rate

Fill the screen with one colour at a time (black, white, red, green and blue) and scan it slowly up close. A dead pixel shows as a black dot on bright colours; a hot or stuck pixel shows as a bright or coloured dot on black. Wipe the screen first, because dust looks similar but keeps its shape across colours. On a black screen in a dark room you will also see backlight bleed or clouding at the edges; some is normal on LCD panels, while bright patches visible in ordinary films are worth returning.

Then check that the monitor is running as advertised. The resolution a browser reports is after system scaling, so a 1920×1080 panel at 125% shows as 1536×864; multiply by the device pixel ratio to get the physical pixels. A 144 Hz or 165 Hz monitor often runs at 60 Hz out of the box, because the operating system picked 60, the cable or port cannot carry more (older HDMI versions are a common limit), or the game is capped. Measure the refresh rate, and if it reads 60, look at the display settings and the cable before suspecting the panel.

• Every key registers once, and typing produces no doubled letters
• The key combinations you use in games all register together
• Each mouse button, side buttons included, counts exactly one click per press
• The wheel scrolls the right way every time, in both directions
• No dead, hot or stuck pixels on black, white, red, green and blue
• Resolution and refresh rate match the specification after checking scaling and cable