Screen fills your whole display with a solid colour or pattern so you can spot dead pixels (always black), stuck pixels (always one colour), backlight bleed and uniformity issues. Pick a colour to go full-screen, then click or press → / ← to cycle, and Esc to exit. Nothing is uploaded.

For dead pixels, view the solid black and white fields closely; for stuck pixels, cycle through red, green and blue. Backlight bleed shows up as lighter patches on the black field in a dark room. This uses the browser's full-screen mode; some content around the very edges may be cropped by the browser chrome. Everything runs on your device.