Screen Tester

This free screen tester fills your display with a full suite of diagnostic patterns so you can check a monitor, phone or laptop end to end. It matches or beats the popular monitor test sites, in one place: solid colors for dead and stuck pixels, gradients for banding, grayscale and contrast wedges plus PLUGE black-level and white-clipping bars, a 1 pixel checkerboard for sharpness and moiré, uniformity zones for backlight bleed, a geometry grid with circles for convergence, and a text-rendering page. Every test tile names what it checks, and the fullscreen overlay tells you exactly what to look for while it runs.

For motion and panel behaviour there's a response-time block, a ghosting sweep, a PWM backlight-flicker line, a pixel-inversion pattern, chasing squares for motion clarity, and a frame-skipping test for display overclocking. A live display-info readout reports the measured refresh rate, resolution, pixel scaling and HDR / wide-gamut support, and a stuck-pixel fixer flashes rapid colors to jog stuck subpixels back to life. A handful of pro tests that need external hardware — high-speed-camera scan-out, oscilloscope flicker capture, true variable-refresh simulation — are left out because a web browser can't drive them meaningfully.

Dead pixels stay black on every color; stuck pixels stay lit on one channel. Use ←/→ to move between tests,↑/↓ or click to cycle variants,+/− to adjust the active option, andEsc to leave.