डेड पिक्सेल टेस्ट.

Visual inspection only: the browser cannot detect defective pixels automatically, and this tool does not repair stuck pixels. Full screen depends on browser support; where it is unavailable, such as on iPhone, the colors fill the page instead.

Each color fills the whole display at full intensity. Automatic mode changes color every 3 seconds; there is no rapid flashing. The cursor and instructions hide after a moment so they are not mistaken for a defect.

A dot that stays black on white and colored screens is a dead pixel; a dot that remains bright red on black is a stuck subpixel.