How to use
- Solid colorsArrow keys to switch
Show solid colors full screen
- A white-screen dotPress M to note it
Find a dot and mark its spot
- Color and position notesin px and %
Copy the color and position notes
Dim the room, wipe the screen and press “Start full-screen test”. If real full screen is unavailable, the test covers the whole page instead.
Cycle through solid black, white, red, green and blue while slowly scanning the whole screen. Use the arrow keys, Space, click or tap, or a sideways swipe; set an automatic interval if you like.
When you see a small dot, put the cursor on it and press M (or “Mark spot” in the control bar) to note the color and position.
Under “Patterns”, check gradients, gray steps, a 1 px checkerboard and lines, small text and a grid for banding, blur and distortion.
Below, review resolution, devicePixelRatio, color gamut, HDR and the estimated refresh rate. Press Esc to leave full screen.
What it does
Eleven solid screens
Black, white, red, green, blue, cyan, magenta, yellow, 50% gray, dark gray and light gray in full screen. The control bar tells you what to look for on each.
Easy to step through
Left/Right arrows, Space, click or tap, and sideways swipe move forward; the Left arrow or a swipe to the right goes back; an automatic interval is available. The cursor and control bar hide when idle.
Gradient, line and text patterns
Smooth gradients, 32 gray steps, a 1 px checkerboard and lines, small text and a grid. 1 px patterns are not exactly one pixel when page zoom or display scaling is not 100%.
Notes on where you looked
Mark a suspicious dot with its color and an on-screen position (px and %). Notes live only while the page is open and can be copied to send to the seller.
Screen info and refresh rate
Shows screen size, devicePixelRatio, estimated physical resolution, color depth, color-gamut and dynamic-range (HDR), and estimates the refresh rate from paint timing.
Flashing pattern with a notice
A white/black flashing pattern is available only after you confirm a photosensitivity notice, and never when the system asks to reduce motion.
Use cases
- Check a new or used monitor or laptop for dead or stuck-on pixels
- Tell a pixel fault apart from dust or a smudge on the screen
- Keep a record of the screen’s condition before contacting the seller or maker within the warranty
- Look for image retention after the same image was shown for a long time
- See whether the refresh rate you set is roughly what the browser reports
Capability matrix
| Feature | Support | Notes |
|---|---|---|
| Visual check for dead or stuck pixels with full-screen solid colors | Supported | — |
| Automatic detection of bad pixels | Not supported | Browsers cannot read what the screen shows, so you look by eye |
| Deciding whether the panel is physically faulty | Not supported | Telling dust, smudges and display settings apart from a fault is up to your eyes and the seller or maker |
| Repairing or “fixing” stuck pixels | Not supported | This tool is for checking only |
| Refresh rate | Partial | An estimate from paint timing; browser limits and power saving can make it read lower than the real rate |
| Color gamut and HDR | Partial | What the browser and OS report, which may differ from the monitor’s specification |
| Color accuracy measurement (calibration, ΔE) | Not supported | Needs a colorimeter |
| True full screen | Partial | Where the browser lacks it (such as Safari on iPhone) the test covers the page and browser bars may remain |
Limits & notes
- Judging bad pixels is a visual call. How many are covered by a warranty differs by product and maker.
- Unless page zoom and OS display scaling are 100%, 1 px patterns do not map one-to-one to pixels.
- The refresh rate is estimated from about 1.2 seconds of frame timing and changes with load from other tabs and power-saving settings.
- Resolution, gamut and HDR values are what the browser and OS report. With several monitors, they belong to the one holding this window.
- It opens on phones and tablets, but the small screen and limited full-screen support make a PC (including an external monitor) the better choice for checking dots.
Privacy & safety
Screen information is read and shown inside your browser only — nothing is stored or sent, and notes vanish when you close the page.
FAQ
What is a dead pixel, and how is it different from a stuck pixel?
Can this fix a dead or stuck pixel?
Is the dot dirt or a bad pixel?
The refresh rate reads lower than my setting
It does not go full screen, or Esc does not exit
Is the screen info or are my notes sent anywhere?
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