Monitor Test — Check Your Screen Online
This monitor test fills your screen with the patterns that make display faults visible — solid colors, gray patches, gradients and moving objects — so you can see within a couple of minutes whether your panel has a defect worth returning it for.
Everything runs in the browser. There is nothing to install and no calibration hardware needed, because every one of these checks is judged with your own eyes against a pattern the page draws at full screen.
How to test your monitor online
Clean the screen first with a dry microfibre cloth. A speck of dust reads exactly like a stuck pixel and most "dead pixel" panics end at this step. Then turn the room lights down, set your browser to 100% zoom, and put the page into full screen so no toolbar or wallpaper is left in view.
Work through the five patterns in order, one at a time, and look at the whole panel rather than the centre — edges and corners are where uniformity and backlight problems show up. Do the whole pass again with your head straight on, roughly an arm's length away, because several display faults change or vanish with viewing angle and that is itself a diagnostic clue. If the monitor is new, do this on day one — return windows are short.
What this monitor test checks
The tool is split into five patterns, each aimed at a different class of defect. Run all five: a panel can be flawless on solid colors and still band badly on a gradient, or look perfect standing still and smear the moment anything moves.
Dead and stuck pixels
Eight full-screen colors — black, white, red, green, blue, magenta, cyan and yellow — cycle with a click or the space bar. A dead pixel stays black on every one of them; a stuck pixel stays lit in one color while the screen around it is black. The dedicated dead pixel test goes further into sub-pixel faults, phone and tablet screens, and what your warranty is likely to cover.
Panel uniformity and backlight bleed
Four flat patches — 100% white, 75% light gray, 50% mid gray and 15% charcoal — reveal whether brightness and tint are even across the panel. Clouding, corner glow and a warm patch in the middle all show here and nowhere else. The screen uniformity test covers how to separate backlight bleed from IPS glow before you start a return.
Color gradients and banding
Grayscale, red, green and blue ramps run from black to full intensity. A good 8-bit panel draws them as a smooth wash; visible steps mean banding, usually from a 6-bit panel faking colors with dithering, or from a GPU output set to a limited range. The monitor color test explains how to read those steps and what is fixable in software.
Gamma
A finely striped square sits inside a flat mid-gray field. Step back about a metre and squint: at gamma 2.2 the stripes blend into the surrounding gray and the square disappears. If the square looks lighter than its surround your gamma is low and the picture will look washed out; darker means gamma is high and shadow detail is being crushed. The gamma test walks through correcting it in the monitor menu and the OS color profile.
Motion, ghosting and response time
A block moves across the screen at a speed you control with a slider. Trails behind it are ghosting — pixels that are too slow to finish a transition. A bright or inverted halo in front of it is overshoot from overdrive set too aggressively. The monitor ghosting test covers finding the overdrive setting that removes trails without introducing halos.
Testing a laptop, phone or TV screen
The same patterns work on any screen with a browser, and a laptop panel is the most common thing people check here — it is the display you cannot swap without replacing the machine. On a laptop, make sure automatic brightness and any ambient-light adaptation are off first, or the uniformity patches will shift while you are looking at them.
On a phone or tablet, disable auto-brightness, true tone and night mode, and hold the device still: OLED panels shift color slightly with angle by design, so a tilt reads as a defect when nothing is wrong. On a TV, turn off motion interpolation and any dynamic contrast or eco mode before the uniformity pass, because those features actively change brightness scene by scene.
What a browser can and cannot measure
This monitor test shows you defects. It does not measure them in numbers, and any site that claims otherwise from a web page is guessing.
A browser cannot read your panel's response time in milliseconds. Gray-to-gray figures in reviews come from a photodiode and an oscilloscope pointed at the screen; the moving block here tells you whether trailing is visible to you at your refresh rate, which is the thing that actually affects how a game looks. It cannot measure color accuracy either — Delta E needs a colorimeter held against the glass, so the gradient and gamma patterns tell you about banding and tone response, not about how accurate your reds are.
The page also cannot confirm your refresh rate on its own. Animation is driven by the browser's frame callback, which is capped by whatever mode the OS has actually selected, so a 144 Hz monitor stuck at 60 Hz produces smooth motion at 60 fps and nothing on the page looks wrong. Check the refresh rate in your display settings and in the monitor's own on-screen menu, which reports the signal it is really receiving. And a screenshot will never capture any of these faults: they live in the panel, not in the image, so only a photo taken with another camera shows someone else what you are seeing.
Common display faults and what they mean
A black dot on every color is a dead pixel — the transistor is off for good and no software fix exists. A colored dot on black is a stuck sub-pixel, which occasionally recovers after a pixel-cycling video or gentle pressure. Brighter patches at the edges or corners are backlight bleed if they stay put when you move your head, and IPS glow if they fade as you look straight on — glow is a property of the panel type and is not a defect any replacement will fix.
Steps in a smooth gradient point at bit depth or a limited RGB range in the GPU driver rather than a broken panel. Trails behind moving objects are slow pixel transitions; halos in front of them mean overdrive is turned up too far. A faint flicker at low brightness is usually PWM backlight dimming, which is normal behaviour for the panel and the reason some people get headaches on one monitor but not another.
Frequently asked questions
How do I test my monitor's resolution, response time and refresh rate?
Resolution and refresh rate come from your OS display settings and the monitor's on-screen menu; response time you check by eye with a moving pattern. Set the resolution to the panel's native value, confirm the refresh rate in both the OS and the monitor menu so you know the signal really arrives, then run the motion pattern and look for trails. A browser cannot put a millisecond figure on response time — that needs a photodiode rig.
What problems should I check for when a new monitor arrives?
Dead pixels, backlight bleed, uniformity, gradient banding and ghosting — in that order, on day one. Cycle the solid colors for pixel faults, view the dark gray patch in a dim room for bleed and clouding, check the gray ramp for visible steps, then run the motion pattern. Do it inside the retailer's return window, because swapping the unit at the shop is far easier than arguing a panel defect through a manufacturer warranty later.
Is it a dead pixel or a stuck pixel, and how do I tell if a sub-pixel is dead?
Look at it on white and on black. A dead pixel is black on a white screen and invisible on black. A stuck pixel glows red, green or blue on a black screen. A dead sub-pixel is the harder case: the pixel still lights, but one of its three components is missing, so on a full white screen it looks faintly tinted the opposite color. Dead sub-pixels do not respond to pixel-refresher videos or pressure.
Does my new monitor have backlight bleed or just IPS glow?
Move your head and watch what happens. IPS glow shifts and fades as you change viewing angle, and largely disappears when you sit straight on; backlight bleed stays in exactly the same place no matter where you look from. That distinction decides whether a replacement is worth requesting — glow is inherent to IPS panels and every unit will have it, while bleed is a manufacturing fault and a new panel can be better.
How do I check if my monitor is actually running at 144Hz?
Check two places that disagree only when something is wrong: your OS display settings and the monitor's own information menu. Windows and macOS frequently default a high-refresh panel to 60 Hz, and a cable that is too slow for the mode will silently cap it too. The monitor's menu reports the signal it is genuinely receiving, so if the OS says 144 Hz and the monitor says 60 Hz, the cable or port is the culprit.
How many dead pixels do I need before the manufacturer replaces the monitor?
There is no industry standard — it is set per brand, and the range is wide. Typical policies need somewhere between three and ten dead pixels before a panel qualifies, while several premium lines carry a zero-bright-dot guarantee that covers a single stuck pixel. For one or two defects your fastest route is the retailer's return window, not a warranty claim. Check the exact policy for your model before you buy.
How do I test a second-hand monitor before buying it?
Bring a laptop and run the full pattern set in front of the seller. Cycle the solid colors for dead and stuck pixels, check the dark gray patch for bleed and clouding, look at the gray ramp for banding, then run the motion pattern for trails. Also test every input port with your own cable, and check the panel at native resolution — a monitor that only syncs at a lower mode usually points at a failing port or scaler.