Dead pixel test

Dead (black) pixels — dark specks that never light. The classic first check.

• This test cannot see your screen — it shows known colors full-viewport and your eyes are the detector. No camera, no analysis, no claims about what it found.
• Fullscreen covers the whole panel including browser chrome; without it, the cycle still fills the viewport, which catches most of the screen but not all. Esc exits fullscreen at any time (the browser guarantees it); Space and the on-screen buttons step colors.
• Work through the five colors slowly. A dot that stays dark on white is a dead pixel; a dot that keeps its own color on black is stuck. One sub-pixel channel failing shows only on its color and black — that is why there are three primaries, not one.
• Dust on the panel mimics a dead pixel — clean the screen first. Very small dead pixels can hide at low brightness; the test says nothing about warranty terms, which manufacturers set by count and location.