01
White Screen
Fills your entire screen with solid white. Cleaning the screen, spotting dust and dark…
Blue Screen
Fills your entire screen with solid blue. Checking blue sub-pixels and spotting the colour blotching that some panels show in dark blues.
Screen Tests
Nothing uploaded
No sign-up
Free, unlimited
Press Fullscreen, then look closely at the whole panel.
In short
A full blue screen isolates the blue sub-pixel, and it is the field where a particular class of panel problem shows up most clearly: colour blotching, the uneven mottled appearance that some VA and IPS panels show in dark saturated blues. If the field looks patchy rather than flat, that is what you are seeing, and it is a panel characteristic rather than dirt. Blue is also the hardest field for the eye to judge, because human vision has the fewest blue-sensitive cones — which is why blue text on black is uncomfortable to read and why a dead blue sub-pixel is the least noticeable of the three in ordinary use. That works both ways: a fault here matters less in practice, but it is also easier to miss. One practical note: many devices ship with a blue-light filter or night mode that shifts the whole display warm, and that will make this field look wrong in a way that has nothing to do with the panel. Switch it off before judging anything.
How to use the Blue Screen
- The test starts on its own — no button to press and nothing to install.
- Follow the prompt in the test panel and watch the readings update live.
- Press Reset to start over with a clean slate.
About the Blue Screen
The Blue Screen fills your entire screen with solid blue. Checking blue sub-pixels and spotting the colour blotching that some panels show in dark blues. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.
What people use it for
- Checking blue sub-pixels and spotting the colour blotching that some panels show in dark blues.
- Checking a monitor or phone screen before a return window closes.
- Using as a plain backdrop for photography or for cleaning the screen.
Press Fullscreen above before judging anything. A colour patch surrounded by page furniture tells you very little — the panel needs to be filling the whole screen, ideally in a dark room, with any night-light or blue-light filter switched off.
Frequently asked questions
What is the difference between a dead and a stuck pixel?
A dead pixel receives no power and stays black on every colour. A stuck pixel is latched on and shows the same bright red, green or blue dot against every background. Stuck pixels sometimes recover; dead ones never do.
How do I tell a dead pixel from dust?
Dust sits on the outside of the glass and moves or disappears when you wipe the screen with a microfibre cloth. A dead pixel does not move and stays in exactly the same position on every colour.
How many dead pixels before I can return a monitor?
That depends on the manufacturer's policy, which is usually written against the ISO 9241-307 pixel fault classes. Most consumer panels are sold to a standard that tolerates several sub-pixel faults, so check the specific warranty terms — and photograph what you find while the panel is still within the return window.
Is the Blue Screen free, or is there a paid tier?
Free, unlimited, and no email address required. You can use it a hundred times a day and nothing changes.
Is my data uploaded anywhere?
No. The Blue Screen runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
When would I actually need the Blue Screen?
The jobs it is built for: checking blue sub-pixels and spotting the colour blotching that some panels show in dark blues. Checking a monitor or phone screen before a return window closes. Using as a plain backdrop for photography or for cleaning the screen. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Is there anything to watch out for?
Press Fullscreen above before judging anything. A colour patch surrounded by page furniture tells you very little — the panel needs to be filling the whole screen, ideally in a dark room, with any night-light or blue-light filter switched off.
Does the Blue Screen need an app or a driver?
No installation, no extension and no driver. The Blue Screen uses the browser's own device APIs and begins as soon as the page loads, so there is nothing to press first. Press Reset at any point to start over with a clean slate.
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