Black
Stuck pixels — a dot frozen on red, green or blue glows against the dark. Also the field where backlight bleed at the corners becomes obvious.
Monitor and dead pixel test
Six solid fields, full screen. Your eye finds what code cannot.
- No permission needed
- Escape leaves at any point
- Nothing sent anywhere
Six fields, one at a time: black, white, red, green, blue, grey. Click or press any key to advance, Escape to leave. Look closely at each field — a faulty pixel is a dot that refuses to match its neighbours.
What did you see?
What the browser knows about this screen
Which field shows what
White
Dead pixels — a dot that receives no power stays black. Also the field where dust and marks on the surface show up, so wipe before judging.
Red, green, blue
One subpixel at a time. A pixel can lose a single colour element while the other two work, and only a pure field reveals it.
Grey
Uneven backlight and clouding on LCD panels, and early burn-in on OLED screens. Small variations are normal on almost every panel.
What the check shows
6 — black, white, red, green, blue, grey
Colour fields
requested, and it still works if the browser refuses
Full screen
Escape
Leave at any time
you — a page cannot see your screen
Who finds the fault
size, pixel ratio and colour depth, from the browser
Screen data read
nothing
Anything transmitted
Other ways to check a screen
| Approach | Best for | Trade-off |
|---|---|---|
| A solid-colour image opened full screen | Anyone who already has such a file | Image compression can produce faint blotches that look exactly like screen faults |
| The monitor’s own test pattern | Standalone monitors whose menu offers one, because it bypasses the computer entirely | Not available on laptops, and it proves nothing about the cable and graphics card |
| A pixel-fixing utility | A stuck pixel that might still recover | Needs installing, and it does nothing at all for a genuinely dead pixel |
| This page | A quick check before a warranty claim or before buying a used monitor | Colours are what the browser and the operating system deliver, so a colour profile can shift them slightly |
When this page will not help
Where this stops being the right tool — and what to use instead.
-
You want to calibrate colours
Calibration needs a measuring device held against the screen. Anything a page can show you is judged by an eye that adapts within seconds.
Next step: Use a hardware colorimeter, or the calibration wizard built into your operating system.
-
You are checking a phone screen for burn-in
Burn-in appears as a faint ghost of a previous image and is easiest to see on grey, but browser interface elements sit on top and get in the way.
Next step: The grey field here is a reasonable start. For a proper look, use a full-screen grey image in a gallery app with the interface hidden.
-
The screen flickers
Flicker is usually the cable, the refresh setting or the backlight driver, and none of them changes with the colour on screen.
Next step: Reseat the cable, try another one, and check the refresh rate in display settings.
-
You want to prove a warranty claim
A photograph of a screen is poor evidence, and manufacturers apply their own thresholds for how many faulty pixels justify replacement.
Next step: Find your manufacturer’s pixel policy first, then count against that. It decides the outcome more than any test does.
Words you will meet on this page
- Dead pixel
- A pixel that stays dark on every colour, because it receives no power. It shows as a black dot on the white field and never recovers.
- Stuck pixel
- A pixel frozen on one colour, usually red, green or blue. Visible on the black field. Unlike a dead pixel it sometimes recovers by itself or with gentle pressure.
- Subpixel
- Each pixel is built from a red, a green and a blue element. Showing pure colours in turn is what reveals a fault in one element rather than the whole pixel.
- Backlight bleed
- Light leaking around the edges, seen on the black field as pale corners. Common on LCD panels and normal in small amounts.
- Clouding
- Uneven brightness across a dark screen, looking like patchy fog. Best seen on the grey field, and largely a property of the panel rather than a defect.
- Pixel ratio
- How many physical pixels the screen packs into one CSS pixel. A ratio of 2 means a fault occupies a quarter of the area you might expect.
- Burn-in
- A permanent ghost of an image left on OLED screens after long static display. Visible on grey, and not repairable.
Screen questions people actually ask
Dead or stuck — how do I tell?
Look at the black field and the white field. A dot that is black on white is dead: it gets no power. A dot that glows on black is stuck: it is frozen on. Stuck pixels sometimes recover; dead ones do not.
Can a stuck pixel be fixed?
Sometimes. Rapidly cycling colours over the area, or very gentle pressure with a soft cloth on a switched-on screen, occasionally frees one. Press hard and you will make more faults than you fix.
How many faulty pixels justify a replacement?
It depends entirely on the manufacturer, and the thresholds are often surprisingly high — several pixels on a large panel can be within specification. Find your manufacturer’s pixel policy before contacting support.
The corners glow on the black field.
That is backlight bleed, and a small amount is normal on almost every LCD. It is a fault only when it is severe enough to be visible in ordinary use rather than in a dark room on a black screen.
Does this send anything about my screen?
No. It reads the size, the pixel ratio and the colour depth that the browser already exposes to every page you visit, and shows them to you. Nothing is transmitted and nothing is stored beyond a one-line verdict in your own browser.
Why does it ask me for the verdict?
Because a web page cannot see your screen. Any automatic result would be invented. Here the page provides the fields and you provide the observation — that division is the honest one.
Full screen did not happen.
Some browsers and some policies refuse the full-screen request. The colour fields still fill the window, which is enough for the check; you simply have a browser frame around the edge.
How do I get out?
Press Escape at any point. Clicking advances to the next colour, and after the last one the check ends by itself.
Should I check a monitor before buying it used?
Yes, and this is the fastest way. Six solid fields take under a minute and reveal dead pixels, stuck pixels and heavy backlight bleed — the three things a seller’s photographs will never show.
The colours look wrong.
Colour profiles applied by the operating system can shift them. That matters for calibration and not at all for finding faulty pixels, which are about a dot being the wrong colour from its neighbours.
Does it work on a phone?
Yes, though the browser interface takes up part of the screen. On an OLED phone the grey field is also the best way to spot early burn-in.
The screen has a permanent faint shape on grey.
On an OLED screen that is burn-in from something displayed for a very long time. It is permanent and not repairable, though it usually only matters if it is visible during normal use.