DeviceChecker
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Screen & Dead Pixel Test

Inspect your monitor, laptop screen, or mobile display for dead pixels, stuck subpixels, backlight bleed, and real-time hardware refresh rate.

1920 × 10801x DPR

Hardware Screen Resolution • 24-bit Color • SDR

Refresh Rate: Measuring...
Tested: 1 of 9 patterns

How screen and dead pixel verification works

Web browsers cannot physically count defective pixels through code. Instead, this tool displays pure, uncompressed solid color fields across 100% of your display. Inspect the screen closely: any pixel that remains permanently black on white/color screens is a dead pixel, while any pixel that stays stuck on a specific color on black is a stuck subpixel.

Pure Black (#000000)

Highlights stuck subpixels (white, red, green, blue) and reveals backlight bleed or IPS glow.

Click “Start Fullscreen Test” for an unobstructed inspection across all edges of your monitor.

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Direct Color PaletteClick any swatch to inspect that color field immediately

Three Steps for an Accurate Screen Inspection

  1. Clean Your Screen First: Gently wipe away surface dust, smudges, and fingerprints with a dry microfiber cloth before testing — surface specks are frequently mistaken for dead pixels.
  2. Dim Ambient Room Lights: Turn off overhead office fluorescents or close blinds to minimize external reflections on glossy panels and reveal subtle backlight bleeding along the bezels.
  3. Cycle Every Primary & Secondary Color: A pixel might appear functional on white or blue, but have a defective green subpixel that only shows up as a dark void on green or magenta.

Understanding Screen & Pixel Defects

How modern LCD, LED, and OLED display panels work and how to diagnose hardware defects

Dead vs. Stuck Pixels

Every screen pixel consists of red, green, and blue (RGB) subpixels controlled by microscopic thin-film transistors. A dead pixel has lost power entirely and cannot pass light, appearing black across light backgrounds. A stuck pixel has one subpixel locked in the “on” state, appearing as a persistent red, green, or blue dot on dark backgrounds.

Backlight Bleed & IPS Glow

Backlight bleeding happens on LCD panels when light from the backlight LEDs escapes around the edges or corners due to uneven pressure in the bezel frame. To test for it, enter fullscreen mode on the Pure Black pattern in a dark room. Unlike IPS glow (which changes with your viewing angle), real backlight bleed remains fixed in place.

Display Refresh Rate (Hz)

Refresh rate measures how many times per second your monitor redraws the image. Our test times consecutive browser animation frames against high-precision hardware clocks to measure your live display frequency. If a 144Hz monitor measures 60Hz, your operating system display settings need to be updated.

Troubleshooting Common Issues

Quick fixes if your hardware is not responding as expected.

Display refresh rate is capped at 60Hz on a high-refresh monitor
Open your OS display settings (Windows: Settings > System > Display > Advanced display; Mac: System Settings > Displays) and verify your monitor is set to 120Hz, 144Hz, or higher. Also ensure hardware acceleration is enabled in Chrome/Edge under Settings > System > "Use graphics acceleration when available".
Cannot enter fullscreen mode on iPhone or iPad
Mobile Safari on iOS restricts the HTML5 Element.requestFullscreen() API to prevent web pages from completely hiding system navigation chrome. On iPhone, inspect the colors directly inside the large interactive test pad. For a completely borderless experience, tap the Share button in Safari, select "Add to Home Screen," and open DeviceChecker as a standalone web app.
Unsure whether a mark is surface dust or a real dead pixel
Gently wipe the area with a dry, clean microfiber cloth. Move your head slightly from left to right: if the dot shifts position relative to the LCD grid behind the front glass, it is a surface speck. If it stays precisely fixed to the subpixel matrix, it is a panel defect.
Not sure which browser engine, GPU, or color depth you are running?
Visit our dedicated Browser & Device Info tool to inspect your active browser engine, WebGL vendor, and display color depth in detail.

Browser & OS Compatibility

All screen diagnostic patterns execute using standard HTML5 and Fullscreen Web APIs

Browser Compatibility

Confirmed hardware API support across major desktop and mobile browsers.

Browser hardware API feature support breakdown
Feature / DiagnosticChromeFirefoxSafariEdgeNotes
HTML5 Fullscreen API (Element.requestFullscreen)FullFullFullFullNative fullscreen on desktop and Android; iOS Safari uses inline maximized canvas.
High-Precision Refresh Rate Timing (requestAnimationFrame)FullFullFullFullCalculates live display refresh rate synchronized to the display vsync interrupt clock.
HDR Dynamic Range Detection (@media dynamic-range)FullFullFullFullIdentifies High Dynamic Range monitor capabilities and deep color support.
TrueColor & DeepColor Bit Depth (screen.colorDepth)FullFullFullFullReads 24-bit (8-bit per channel) or 30-bit+ (10-bit HDR) color palette depth.

Frequently Asked Questions

Everything you need to know about this hardware diagnostic.

What is the difference between a dead pixel, a stuck pixel, and a hot pixel?
A dead pixel occurs when the entire pixel transistor completely loses power and fails to transmit light, leaving a permanent black or dark defect across white and colored screens. A stuck pixel happens when one of the subpixel color channels (red, green, or blue) gets physically locked in an open state, appearing as a bright, persistent colored dot on black or dark backgrounds. A hot pixel is when all three RGB subpixels remain permanently on at full intensity, creating an unyielding white dot even on pure black.
Can a stuck or dead pixel be fixed with software?
A truly dead pixel (where the underlying transistor has burned out or severed electrical contact) cannot be repaired through software. However, stuck subpixels (where the liquid crystal molecules inside the cell are temporarily frozen or jammed) can occasionally be unstuck by rapidly alternating high-contrast primary colors at high speed to agitate the liquid crystal material, or through gentle localized massage with a damp microfiber cloth while cycling colors. Results vary depending on the panel technology (TN, IPS, VA, or OLED).
Why does my 144Hz, 165Hz, or 240Hz monitor show only 60Hz on the refresh rate meter?
If you have a high-refresh-rate gaming monitor but the meter measures ~60Hz, the monitor is almost always running at default operating system settings. By default, Windows and macOS often configure new or external displays to 60Hz for compatibility. Open Windows Settings > System > Display > Advanced display (or macOS System Settings > Displays) and manually select your monitor’s highest available refresh rate. Also ensure your HDMI or DisplayPort cable supports the required bandwidth, and verify that browser hardware acceleration is enabled in your browser settings.
What is backlight bleed versus IPS glow?
Backlight bleed is a hardware defect where the edge seals of the monitor frame are slightly loose or misaligned, allowing white light from the backlight LEDs to spill out around the bezel borders in fixed, uneven patterns regardless of your viewing angle. IPS glow, in contrast, is an inherent optical characteristic of IPS (In-Plane Switching) panel technology where diagonal viewing angles allow light to pass through the polarized liquid crystal layers, creating a mild golden or silvery sheen in the corners that shifts or disappears as you change your viewing position.
Can I test dual monitors or multiple displays with this tool?
Yes. To test a second or third monitor, simply drag your browser window onto that display and click "Start Fullscreen Test." The Fullscreen API expands specifically to the monitor that contains the active browser window. If you have different monitors with different resolutions or refresh rates (e.g. an external 144Hz monitor connected to a 60Hz laptop), each screen can be tested independently.
Are any screenshots, webcam feeds, or display recordings captured or uploaded?
Never. DeviceChecker operates under a strict zero-upload client-side architecture. This screen test generates pure solid RGB color fields entirely within your browser DOM. No display frames are captured, no screenshots are saved, and zero telemetry is transmitted to any server. Your testing session exists exclusively in your personal browser memory.

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