Screen tests

The dead pixel test fills the screen with one flat colour at a time. A pixel that stays black on every colour is dead — its subpixels receive no power. One that stays lit in a single colour is stuck, and those sometimes recover on their own. Cycling through several colours matters because a subpixel failure is invisible against a background of its own colour.

The resolution test reports what the browser sees, which is not always what the monitor can do. A 4K display running at 1080p, or a scaled desktop reporting a device pixel ratio above 1, both show up here, and both explain a picture that looks softer than it should.

Refresh rate is measured by timing how often the browser can present a frame. It is worth checking after enabling a high-refresh mode, changing cable or port, or connecting an external monitor that may have quietly fallen back to 60 Hz.