About ScreenTest

ScreenTest is a set of free display tests that run in your browser. They exist to answer one practical question quickly: is something wrong with this screen, and if so, what?

How the tests work

Most display defects — dead pixels, backlight bleed, poor uniformity, banding, burn-in, ghosting — are easy to see once the screen shows the right pattern and almost invisible otherwise. Each test shows the pattern that makes one problem stand out, explains what “good” and “bad” look like, and tells you what to do about it.

• Patterns are drawn, not downloaded. Solid colors, gradients and test patterns are rendered live in your browser at your screen’s native resolution, so they are pixel-exact on any display, from a phone to an 8K TV.
• Pixel-level patterns are drawn in device pixels. Tests such as gamma and sharpness depend on single-pixel lines. We draw them at your display’s physical pixel grid and warn you when browser zoom or display scaling makes an exact 1:1 mapping impossible.
• Motion is timed to your display. Motion tests measure your refresh rate first and move objects at a fixed speed in pixels per second, so a 60 Hz laptop and a 360 Hz monitor see the same test.
• Refresh rate is measured precisely. Instead of counting frames per second, the refresh rate test fits a line through every frame timestamp, which gives an accurate reading in a couple of seconds and stays accurate even when the odd frame is dropped.

What a browser can and can’t measure

We are careful not to claim more than a web page can do. A browser has no access to a light sensor, so no web page can measure brightness in nits, color error (ΔE), contrast ratio, PWM frequency or the input lag of the panel on its own. Where that matters, our guides explain the reliable alternatives — a colorimeter for calibration, the camera methods for flicker and input lag — and what you can still judge by eye.

Privacy

Every test runs entirely on your device. We don’t upload anything, there are no accounts, and the site sets no tracking cookies. A few tests remember your last setting (for example a gray shade) in your browser’s local storage, which never leaves your device. See the privacy page for details.

Feedback

If a test doesn’t work on your device or something in a guide is wrong, we want to know — accuracy matters more to us than anything else on this site.