MonitorTester
MonitorTester is a free online screen test that runs entirely in your browser — no download, no account, no uploads. It renders the full set of display diagnostic patterns: solid white/black, pure RGB fills, multi-step grayscale ramps, gradients, color bars and motion sequences. In a couple of minutes you can check for dead or stuck pixels, backlight bleed, corner vignetting, Dirty Screen Effect, banding, colour tint and OLED burn-in, and read out your panel resolution, pixel density and refresh rate. Dedicated pages cover screen test, colour calibration, burn-in, resolution, refresh rate and HDR, with a built-in colour picker. TV users can navigate with remote arrow keys; it works on desktop monitors, laptops, phones and tablets. Useful when checking a new monitor inside the return window, inspecting a used display before buying, or verifying a multi-monitor setup.