Screen Fingerprinting Explained

What every page can read

Web pages need display information to lay themselves out, so browsers expose it freely through window.screen and related properties:

• Screen resolution — the full pixel dimensions of your display.
• Available size — the screen minus taskbars and docks, which hints at your operating system and its configuration.
• Color depth — bits per pixel, usually 24 or 30.
• Device pixel ratio — the scaling factor between CSS pixels and physical pixels; high-density displays and OS zoom settings push this above 1.
• Viewport size — the current inner window dimensions, which change as you resize.

Broad categories, useful intersections

A 1920×1080 screen at 1× pixel ratio describes an enormous population, which is why the analyzer rates common configurations Lower distinguishing power. But the values sharpen quickly at the edges: unusual monitor sizes, multi-monitor setups, fractional scaling factors like 1.25 or 1.5, and uncommon available-size values (from a moved taskbar, for instance) each shrink the matching group. And even a common resolution contributes to a combined fingerprint by intersecting with WebGL, font, and canvas signals.

Screen versus viewport — an important distinction

Resizing your browser window changes the viewport, not the screen values. Fingerprinting scripts know this and rely on the stable screen properties rather than the window size. The analyzer reports both so you can see the difference yourself: run it, resize the window, and run again and compare — the viewport value changes while resolution, color depth, and pixel ratio stay put.

What this site's test does

The analyzer reads the values listed above and displays them directly — for screen data, the readable values are more informative to you than a hash. It flags whether your resolution is on a list of widely used configurations and rates the result accordingly. Nothing is uploaded or stored.

Defenses and their limits

Screen values are hard to change meaningfully in daily use — you are not going to buy a different monitor for privacy. The realistic mitigations are at the browser level: Tor Browser letterboxes content into standard window sizes so many users report identical dimensions, and Firefox's resist-fingerprinting mode rounds window sizes similarly. For everyone else, the practical takeaway is awareness: screen data is a small, stable contribution to your fingerprint that costs sites nothing to collect. The reduction guide puts it in context.