Online Screen Test
It works out of the box on Macs, Windows computers, iPhones, iPads, and Android devices. The test pattern displays full-screen in the browser, without the need to install an app or upload an image.
Dead pixels, bright spots, or dust on the screen surface?
Dead pixels usually remain black on a bright background such as white; bright or stuck pixels are more obvious on a black background and may always appear red, green, blue or white. After discovering a suspicious location, change several colors to observe the same point.
Wipe the screen clean before checking, and also pay attention to scratches and bubbles on the protective film. Dust, scratches, and reflections change with cleaning, lighting, or viewing angles; pixel anomalies are often fixed in the same location.