A dead pixel test is the fastest way to check a screen before you buy a used iPhone, unbox a new iPad, or trust a refurbished Mac. This tool fills your display with pure, full-screen solid colors — the exact condition under which a faulty pixel gives itself away. A pixel that stays black on white, white on black, or shows the wrong colour is easy to miss during normal use, but impossible to hide against a flat field of red, green or blue.
It runs entirely in your browser. Nothing is installed, nothing is uploaded, and it works the same on an iPhone, iPad, Mac, or any external monitor. If you do find a stuck pixel — one frozen on a single colour rather than fully dead — the built-in fixer flashes rapid colour noise over that area, which can jolt a stuck sub-pixel back to life.
How to use it
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1Start the test
Tap “Start pixel test”. Your screen fills edge to edge with the first solid colour. On a Mac, it also enters true full screen.
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2Cycle through the colours
Tap (or click) anywhere to move to the next colour: red, green, blue, white, black, then greys. Each one exposes a different kind of fault.
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3Look for anomalies
Scan slowly. A dead pixel stays black on every colour. A stuck pixel shows one wrong colour. A hot pixel stays lit on black. Bring your face close — they’re tiny.
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4Run the fixer if needed
Found a stuck pixel? Exit, tap “Run fixer”, and hold the flashing area over the stuck pixel for a few minutes. Repeat if it partially recovers.
Frequently asked questions
What is the difference between a dead pixel and a stuck pixel?
A dead pixel receives no power and stays black on every colour — it usually can’t be fixed in software. A stuck pixel is frozen on one colour (often red, green or blue) because a sub-pixel is jammed on; these can often be revived with the fixer, which rapidly cycles colours to exercise the sub-pixel.
Can this really fix a stuck pixel?
Sometimes. The fixer flashes rapid colour noise to force the sub-pixel to switch states repeatedly, which can unstick it. It works best on genuinely stuck (not dead) pixels, and may need several minutes and a few attempts. It cannot repair physical damage.
Does the dead pixel test work on iPhone and iPad?
Yes. It fills the whole screen using a full-viewport overlay, so it works in Safari on iPhone and iPad exactly as it does on a Mac or Windows monitor. Turn brightness up and disable auto-lock for the clearest result.
Will testing or fixing damage my screen?
No. Showing solid colours or flashing patterns is completely safe for any display. The fixer simply changes pixels quickly, which is well within normal operation.