How it works
The test fills the whole screen through the WHATWG Fullscreen API with solid colours, gradients and a fine checkerboard. On solid colours a dead pixel stays black, a stuck pixel stays one bright colour, and on black you can spot backlight bleed or glow at the edges. Gradients reveal banding and uneven colour; the checkerboard shows flicker or blur.
The information panel uses the CSSOM View standard: screen.width and screen.height in CSS pixels, window.devicePixelRatio (how many device pixels make one CSS pixel), the size of the browser window, colour depth and the colour-gamut and dynamic-range media queries. The refresh rate is estimated from the timing of animation frames.
What to look for
- Dead pixel: a dot that stays black on every colour, best seen on white.
- Stuck pixel: a dot that stays red, green or blue, best seen on black or the opposite colour.
- Backlight bleed or glow: lighter patches at the edges or corners on the black screen (look in a dim room).
- Banding or tint: visible steps or colour shifts in the grey gradient.
Pixels, CSS pixels and DPR
Web pages are laid out in CSS pixels. On high-density screens one CSS pixel covers several device pixels; the ratio is the device pixel ratio. Display scaling in the operating system (for example 125 % or 150 %) changes the DPR, so the screen size in CSS pixels shrinks while the physical resolution stays the same.
pixels = CSS px × DPR · e.g. 1536 × 864 at 125 % = 1920 × 1080
Tips
- Check a new monitor or laptop as soon as it arrives: many shops only accept pixel-fault returns within a short period, and the rules differ by brand.
- Look from straight in front and from about 30–50 cm away; then step back to judge whether a fault is visible in normal use.
- If the measured refresh rate is lower than your monitor supports, check the refresh rate setting in your operating system and the cable you use.
Standards and sources
- CSSOM View Module (screen, devicePixelRatio) · W3C
- Fullscreen API Standard · WHATWG
- Window.devicePixelRatio · MDN Web Docs
Last reviewed October 18, 2026
Frequently asked questions
How do I find a dead or stuck pixel?
Start the full-screen test and look closely at each colour. A dead pixel is dark on every screen; a stuck pixel shows the same bright colour on black. Note its position, then check it on the other colours.
Why is the resolution shown different from my monitor’s?
The browser reports the screen in CSS pixels and a device pixel ratio. With display scaling the product can be off by a pixel or two, and some systems report the scaled desktop size rather than the panel’s native resolution.
Can a stuck pixel be fixed?
Sometimes a stuck pixel recovers on its own or with gentle pressure, but no web page can repair one reliably, and rapidly flashing “fixer” patterns can trigger seizures in sensitive people, so this tool does not include them. Contact the seller if it is under warranty.