Check a monitor, laptop, phone or TV for dead pixels, stuck pixels and uneven backlight. Step through test colors, scan zone by zone, and tap to mark anything that looks wrong.
Your screen: measuring…
Dead pixel: a dot that stays black on every color (look on white).
Stuck pixel: a dot that stays red, green or blue (look on black).
Backlight bleed: glowing edges or patches (look on black and gray).
During the test: ←/→ change color · G grid · M mark mode · Z undo mark · H hide controls · Esc finish.
Every LCD or OLED screen is made of millions of tiny pixels, each built from red, green and blue sub-pixels. When one of them fails it usually shows up in one of three ways. A dead pixel never lights, so it appears as a black dot on every color and is easiest to spot on white. A stuck pixel has one or two sub-pixels permanently on, so it shows as a red, green, blue (or mixed) dot that is most visible on black and on the other primary colors. A hot or bright pixel is stuck fully on and looks like a white dot on black.
This test fills your screen with pure white, black, red, green, blue and two shades of gray, one at a time, using your browser's full-screen mode. The optional grid divides the screen into labeled zones (A1, B2 and so on) so you can scan methodically instead of letting your eyes wander, and so you can describe exactly where a problem is. Marks you place are saved with their zone and the color you were viewing, which is a good hint about the type of fault: something you noticed on white is likely dead, while something noticed on black is likely stuck or bright.
What a web page can and can't do. No website or app can detect bad pixels automatically; software can't see the physical screen. The test simply shows clean colors so your eyes can find problems. It also can't repair pixels. You'll find "pixel fixer" videos and pages that flash colors rapidly, but they rarely help, and rapid flashing can trigger seizures in people with photosensitive epilepsy, so this tool never flashes.
Backlight bleed and glow. On the black and dark gray screens, LCD monitors often show some light leaking at the edges or corners (backlight bleed) or a silvery glow that changes with viewing angle (common on IPS panels). A little is normal, especially at full brightness in a dark room; large bright patches visible in normal use may be worth reporting.
Warranties. Manufacturers usually publish a pixel policy that says how many and what kind of faulty pixels qualify for a replacement, often based on the pixel-fault classes in the ISO 9241-307 standard. Policies differ by brand and model, so check yours, and test new screens soon after purchase while return windows are open. Copy your summary from this page to describe what you found.
How do I know if it is a dead pixel or just dust?
Dust sits on the surface and usually looks soft or slightly blurry, and it moves or disappears when you wipe the screen. A dead or stuck pixel is sharp, perfectly square and stays exactly in place on every color.
Can this test fix a stuck pixel?
No. Nothing on a web page can reliably repair a pixel, and the rapid-flashing "fixers" you may see elsewhere can be unsafe for people with photosensitive epilepsy. If a pixel is under warranty, contact the seller or manufacturer.
Does it work on phones and TVs?
Yes. Open the page in the phone's browser, or on a smart TV or a computer connected to the TV. iPhones don't allow true full screen for web pages, so on iPhone the colors fill the browser window; scroll slightly or rotate to hide the toolbars.
How many dead pixels are acceptable?
It depends on the manufacturer's pixel policy for your model. Many brands accept a small number of faulty pixels as within tolerance, while some offer "zero dead pixel" guarantees on premium models. Check the warranty terms for your exact model.
Why should I turn off night light or blue-light filters?
Those modes tint every color, so white looks orange and pure blue looks dull. That makes it harder to spot a pixel that is the wrong color.