Dead Pixel Test (ドット抜けチェック) — Free Fullscreen Screen Check

Free dead pixel test to check your monitor for stuck, dead, or discolored pixels. Displays solid black, white, red, green, and blue fullscreen panels so you can spot any dot that looks different from its surroundings. No install required — perfect for checking a used display before buying or a new monitor out of the box.

What is a dead pixel test?

A dead pixel test displays a solid-color image across your entire screen so you can visually check for pixels that are stuck permanently on or off. If a dot appears lit against an all-black background, that's a "stuck pixel." If a dot stays dark against an all-white background, that's a "dead pixel." And if a dot looks like a different color against a solid red, green, or blue background, one of its sub-pixels has likely failed.

Pixel defects happen at a certain rate during manufacturing, and most manufacturers consider a small number of defects per screen to be within spec. Still, if you catch one right after purchase, you may be eligible for a free replacement. Use this tool to check a used display before buying, or a brand-new monitor right out of the box.

How to run a dead pixel test

Dim the room if possible Bright ambient light makes stuck pixels and discoloration harder to spot, so lower the lights if you can before testing.
Check for stuck pixels on black The screen turns solid black. Slowly scan the whole screen for any white or colored dot.
Check for dead pixels on white The screen turns solid white. Look for any dark or black dot.
Check red, green, and blue in turn On each solid color, look for a dot that shows a different color mixed in (a discolored sub-pixel).
Note the location of any defect If you find one, jot down roughly where it is on the screen — this helps when contacting support or requesting a return.

Tips for getting more out of it

Defects are easiest to see when you look straight at the screen. Viewing at an angle can hide them due to reflections and viewing-angle color shift.
Stuck (bright) pixels show up best against black, while dead (dark) pixels show up best against white — always check both, not just one.
Discolored sub-pixels often only become obvious once you compare multiple solid colors side by side, so it's worth cycling through all five test colors.
Check as soon as possible after purchase, since most manufacturers only offer free replacement for defects found within a limited return window (often one week to a month).
Zooming in on a photo of the screen taken with your phone's camera can sometimes reveal a defect more clearly than the naked eye.

When to use this tool

Checking a brand-new monitor or laptop

Run the full test right after unboxing to catch any manufacturing defect early, while you're still within the return window.

Inspecting a used display before buying

Test the actual unit in person before completing a secondhand purchase, so you can decide with your own eyes whether the defects are acceptable.

Deciding whether to request a replacement

Compare what you find against the manufacturer's stated defect policy to judge whether the unit qualifies for an exchange.

Checking a used phone or tablet screen

The same steps work on any device with a browser, including smartphones and tablets.

Periodic health checks on a long-owned display

Re-run the test occasionally on a monitor you've had for years to catch any new defects that develop over time.

Dead pixel terminology

Dead pixel: A general term for a single pixel (or sub-pixel) on a display that fails to change color or brightness normally and stays fixed.
Stuck pixel: A pixel that stays lit even when it should be off (for example, against a black background). Usually caused by one of its red, green, or blue sub-pixels being permanently powered on.
Dead pixel (dark): A pixel that stays dark even when it should be lit (for example, against a white background), typically because power isn't reaching one of its sub-pixels.
Sub-pixel: The red, green, and blue light-emitting elements that make up a single pixel. Every visible color is produced by mixing the brightness of these three; if only one fails, the result is a discolored dot.
Discolored pixel: A pixel that appears the wrong color because one (but not all) of its red, green, or blue sub-pixels has stopped working correctly.
Dead pixel policy: A manufacturer's or retailer's own policy for offering a free replacement or refund once a display has more than a certain number of defective pixels, often stricter than general industry guidelines.
ISO 13406-2: A former international standard that defined four classes of acceptable pixel-defect counts for displays, based on screen size. It has since been superseded, but is still referenced informally in the industry.

Frequently asked questions

It depends on the manufacturer and retailer. Most consider a small number of defects (scaled to screen size) to be within spec, but many offer a stricter "zero dead pixel" guarantee if you report it shortly after purchase. Check the return policy of the store or manufacturer you bought from.

Dead (dark) pixels are generally considered somewhat more common than stuck (bright) ones, though this varies by panel type and manufacturing process. Either way, it's worth checking both black and white right after purchase.

No, this isn't a malfunction. Some browser settings or OS policies block the Fullscreen API from activating. Even when that happens, the solid-color panel still covers your screen normally — you'll just also see your browser's address bar and toolbar.

For stuck pixels, some people try gently massaging the area, which can occasionally help temporarily — but it risks damaging the panel and isn't guaranteed to work. If the display is still under warranty, contacting the manufacturer is the safer option.

Yes. Any smartphone or tablet with a web browser can run the same test. Because the screen is smaller, using a magnifying glass or another camera to zoom in can make defects easier to spot.

Side Note — Why a single failed pixel is still considered "normal"

A Full HD display packs roughly 2 million sub-pixels onto a single sheet of glass, and a 4K display packs in over 8 million. Manufacturing every one of those microscopic circuits flawlessly is extraordinarily difficult, so a certain number of defects are statistically inevitable. To deal with this reality, the display industry long ago settled on standards that treat a small number of dead pixels as within spec rather than a defect.

The most well-known of these was ISO 13406-2, a former international standard that classified pixel defects by type — bright, dark, and so on — and defined how many were acceptable at each of four "classes," scaled to screen size. Many manufacturers built their products to Class II tolerances, and used the standard as justification for denying warranty claims over a handful of dead pixels.

That standard, however, never sat entirely comfortably with consumers. It felt unsatisfying to be told a defect present from day one on an expensive purchase was technically "within spec." In response, some retailers and manufacturers began offering their own stricter guarantees — replacing a unit for even a single dead pixel — as a way to differentiate themselves from the pack.

ISO 13406-2 itself has since been replaced by newer standards, but the underlying manufacturing constraint — that zero pixel defects simply isn't realistic at scale — hasn't gone away. Even with today's high-resolution OLED and LCD panels, running a dead pixel test right after purchase remains a practical way to check, with your own eyes, whether that gap between manufacturing tolerance and consumer expectation actually affects the unit in front of you.

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