How to use it
- Wipe the screen with a soft dry cloth first. Dust and smudges sit on top of the glass and look a lot like bad pixels; a real pixel fault stays in exactly the same spot when you wipe or tilt the screen.
- Turn the brightness up and, for the black and gray screens, dim the room.
- Press Start the test. The page goes full screen; tap or press → for the next colour, tap the left edge or press ← to go back, press a number key to jump to a colour, H to hide or show the instructions, and Esc to leave. The pointer disappears after two seconds so it cannot hide a pixel.
- Look over each colour slowly, edge to edge, from a normal viewing distance and then close up. If you find something, note the colour it shows on and where it is.
- Auto mode (press A) moves to the next colour every 2 to 10 seconds, which is handy when you are checking a TV from the sofa.
What each kind of fault looks like
| Fault | What you see | Best colour to spot it |
|---|---|---|
| Dead pixel | A black dot that never lights | White, then red, green and blue |
| Hot (stuck-on) pixel | A white or bright dot that is always lit | Black |
| Stuck subpixel | A red, green or blue dot that stays on, or a dot missing one colour | Black for a lit dot; cyan, magenta or yellow show a stuck subpixel as a white dot, and the pure colours show a missing one |
| Backlight bleed, clouding | Brighter patches, usually near the edges or corners, on an LCD | Black or gray, in a dark room |
| Pressure marks, uneven areas | Blotches or tinted zones that stay in place | Gray and white |
A colour on screen is made by tiny red, green and blue parts of each pixel. On a white screen all three are lit, so a pixel with a dead part shows as a coloured or dark dot; on black, all three should be off, so anything lit is a fault. Some phone OLED screens arrange their subpixels differently, so a fault there can look slightly different, but the same colours show it.
If you find a fault on something you have just bought, check the manufacturer’s pixel policy and the store’s return window. Policies differ by brand and model, often by how many faults there are and whether they are bright or dark.
Why this test never flashes
Some “stuck pixel fixer” pages flash colours many times a second over the whole screen. We left that out. Flashing that fast and that large is exactly what the Web Content Accessibility Guidelines rule out in success criterion 2.3.1, because flashes at certain rates can trigger seizures in people with photosensitive epilepsy; the rule is no more than three flashes in any one second. Here the colour only changes when you ask, or at most once every two seconds in auto mode.
What we tested
On October 15, 2026, in Chromium 141.0.7390.37, on a 1280 × 720 window at three pixel densities:
| Pixel ratio | Device pixels checked per colour | Pixels not exactly the colour |
|---|---|---|
| 1 | 921,600 (1280 × 720) | 0 of 9 colours had any |
| 1.5 | 2,073,600 (1920 × 1080) | 0 of 9 colours had any |
| 2 | 3,686,400 (2560 × 1440) | 0 of 9 colours had any |
Our first run found the instruction box reappearing after every key press even when you had hidden it, covering about 5% of the screen; H now hides it until you press H again. We also checked arrow keys, number keys, tapping either side, auto mode timing, the hidden pointer, full-screen mode, Esc, and a tap on a 390 px phone screen: all behaved as described, with no page errors.
Tips
- Test a new monitor, laptop or phone as soon as it arrives, while it can still be returned.
- Check a used device before you pay; the full test takes about a minute.
- On a TV, open this page in the TV’s own browser so the picture is not scaled or processed by another device.
- A dot that changes position or vanishes after cleaning was dirt, not a pixel.
Sources
Checked on .
Frequently Asked Questions
Built by Derek Giordano · Part of Ultimate Design Tools