Testing a TV or a wall-mounted monitor with its clunky on-screen browser is painful. Open this page on the big screen once, scan the code with your phone, and the phone becomes the remote: solid colors for dead pixels, gradients for banding, grids for geometry, and a motion pattern for ghosting — switched from your hand.
Solid colors reveal dead pixels (dark dot on white), stuck subpixels (colored dot on black) and backlight bleed (black in a dark room). The gradient exposes color banding, the checkerboard shows contrast and pixel sharpness, the grid shows overscan and geometry — if its outer line is cut off, your TV is zooming the picture — and the moving bar makes ghosting trails visible at a glance.
On screen, keyboard also works: space next pattern, F fullscreen, I info, Esc exit.