Click or press Space / → to cycle colours · Esc to exit

Home Categories Device Testers Screen Test

Screen Test

Find dead pixels, stuck pixels, backlight bleed, and colour issues. Launch a full-screen test and cycle through diagnostic colour fills — no software needed.

Click Enter Full Screen, then scan your display carefully for any pixel that does not match the solid fill colour. Click anywhere or press Space to cycle through all test colours.

Select Starting Colour

⚠ Fullscreen not available in this browser. Use the maximised browser window and scroll away the UI for best results.

Press Esc to exit at any time.

⚫

Black screen

Reveals dead pixels (dark on black), backlight bleed, and IPS glow.

⚪

White screen

Reveals dead pixels (dark on white) and hot/bright spots.

🎨

Primary colours

Red, green, blue — reveals stuck sub-pixels and tint issues.

Screen Resolution

Physical screen pixels

Device Pixel Ratio

Logical Resolution (CSS)

Pixels reported to CSS / JavaScript

Colour Depth

Full Display Report

I see a dark spot that does not move

A stationary dark spot on any colour fill is a dead pixel. Confirm it is on the screen (not dust) by cleaning with a soft cloth. Dead pixels typically cannot be repaired. Check your display manufacturer's warranty policy — many offer a free replacement if dead pixel count exceeds their threshold.

I see a bright coloured pixel on the black screen

A pixel that stays lit in red, green, or blue on a black background is a stuck pixel. Stuck pixels can sometimes be fixed using pixel-cycling software or gentle pressure with a damp cloth (power off first). If it persists for more than a day, it may be permanent.

The full-screen button does not work

Some browsers block fullscreen in certain contexts (e.g. inside an iframe). Try opening the page directly in a new tab. Safari on iOS also restricts fullscreen on some pages. As an alternative, maximise the browser window and use F11 (Windows) or Ctrl+⌘+F (Mac) for a native full-screen browser view.

I see glow in the corners on the black test

Faint milky glow visible at steep viewing angles from the corners is "IPS glow" — a normal optical property of IPS LCD panels. True backlight bleed (visible straight-on) appears as brighter patches near edges. Both may qualify for a warranty return depending on severity.

The screen looks uneven on the grey fill

Variations in brightness across a solid mid-grey indicate backlight non-uniformity. Some variation is normal; a pronounced hot-spot or dark region visible at normal seating distance may indicate a defect. Compare to manufacturer specifications.

The gradient shows visible steps (banding)

Visible banding on the gradient test can indicate limited panel bit-depth (6-bit vs 8-bit), low colour depth in the GPU settings, or an incorrectly configured ICC profile. Check that colour depth is set to 24-bit (True Colour) or higher in your display settings.

💡 How to Use This Tool

Run a complete screen diagnostic in under two minutes:

Choose a starting colour

Select a test colour from the palette — start with Black to reveal dead pixels and backlight bleed.

Enter full screen

Click "Enter Full Screen" to fill your entire display with the solid colour test pattern.

Scan the display

Look carefully across every area of the screen. Any pixel not matching the fill colour is defective. Press Space or click to advance to the next colour.

Check Display Info

Switch to the Display Info tab to view your screen resolution, pixel ratio, colour depth, and orientation data.

📖 About Screen Test

What is the Screen Test?

The Screen Test is a fully client-side browser tool that lets you check your monitor, laptop display, or TV screen for common hardware defects — without installing any software. It uses the browser's Fullscreen API combined with solid-colour canvas rendering and CSS to fill your entire display with diagnostic test patterns, making even a single defective pixel easy to spot against a uniform background.

Common Use Cases

Dead pixel check: Before returning a new monitor or laptop within its warranty window, confirm no pixel is permanently dark.
Stuck pixel detection: Identify pixels that are frozen on one colour even when the screen should display another.
Pre-purchase inspection: Quickly test a second-hand monitor or laptop screen before committing to the purchase.
Backlight bleed check: The black test screen reveals uneven backlight bleed around the edges of IPS and VA panels in a dark environment.
Color accuracy verification: Confirm that your panel renders pure red, green, blue, white, and black without tinting.
Display uniformity: Spot gradients or hot-spots in the backlight across a solid mid-grey fill.

Key Features

Full-Screen Dead Pixel Test

Fills your entire display — including taskbar areas — with a single solid colour. Any dead (dark) or stuck (wrong colour) pixel immediately stands out against the uniform background. Tap or click to cycle through the standard test colours: black, white, red, green, and blue.

8 Test Colour Patterns

Run eight diagnostic patterns: Black (dead pixel), White (hot pixel / bright spots), Red, Green, Blue (primary colour accuracy), Grey (uniformity and gradients), and Colour Gradient sweeps to stress backlight uniformity across the full range.

Display Information Panel

Instantly read your screen resolution, device pixel ratio (DPR), colour depth, available screen area, and orientation — all from the browser's window.screen API without any permissions.

Backlight Bleed Check

A pure-black fullscreen mode in a dark room makes backlight bleed or IPS glow immediately visible around the edges and corners of the panel.

Gradient Stress Test

A smooth gradient from black to white reveals banding — a common defect where a display cannot produce smooth tonal transitions between adjacent brightness levels.

Privacy & Security

This tool is entirely private by design. All test patterns are generated locally using the browser's Canvas API and CSS. No images are downloaded, no data is sent to a server, and no permissions are requested. The tool works offline once the page has loaded.

Technical Details

The tool uses the W3C Fullscreen API (Element.requestFullscreen()), supported in all modern browsers:

Chrome/Edge 15+ — Full support
Firefox 64+ — Full support (as requestFullscreen)
Safari 16.4+ — Full support

Display information is read from window.screen (width, height, colorDepth, pixelDepth) and window.devicePixelRatio.

❓ Frequently Asked Questions

A dead pixel is a display pixel that never illuminates — it always appears black regardless of the image being shown. Dead pixels occur when the transistor that controls the pixel's backlight fails permanently. They are most visible against bright white or solid colour backgrounds.

A dead pixel is always black (the sub-pixel transistor has failed). A stuck pixel is always lit in one colour — red, green, or blue — because one of its three sub-pixels is permanently on. Stuck pixels are easier to spot on a black or opposite-colour background. Some stuck pixels can be fixed with pixel-cycling software; dead pixels typically cannot.

Click "Enter Full Screen" and then use the colour buttons or press the spacebar / arrow keys to cycle through test colours. Look across the entire display for any pixel that does not match the solid fill colour — any dark spot on white, or bright spot on black, indicates a defective pixel.

Stuck pixels can sometimes be fixed by rapidly cycling the pixel between colours (this is what a pixel exerciser does) or by applying gentle pressure with a soft cloth on the affected area while the screen cycles. Success varies by panel type and the specific failure mode. Dead pixels (always black) generally cannot be repaired.

Backlight bleed is light leaking through the edges or corners of an LCD panel when it cannot completely block the backlight. It is most visible on a pure black screen in a dark room. IPS panels typically show more bleed than VA panels. A small amount is considered normal; significant bleed that affects content viewing may be grounds for a warranty return.

Some degree of IPS glow — a milky sheen near corners at extreme viewing angles — is normal on IPS LCD monitors. True backlight bleed (visible straight-on from a normal seating position) may indicate a manufacturing defect. Compare your monitor to your manufacturer's dead pixel and backlight bleed policy before raising a warranty claim.

Version History

1.0.0

Initial release with full-screen dead pixel test, 8 colour patterns, display info panel, gradient test, and backlight bleed mode.

May 30, 2026

Raakkan (Sankar)

AI-driven Full Stack Developer

Indie developer from Tamil Nadu building fast, privacy-first web tools. Creator of Lovable Tools — a growing collection of free utilities and AI-powered tools.

GitHub Profile About Me