Font Fingerprinting: How Your Installed Fonts Track You Online

What Is Font Fingerprinting?

Font fingerprinting is a browser tracking technique that identifies your device by detecting which fonts are installed on your system. Your operating system ships with a default set of fonts, and over time you may install additional fonts — for specific software, language support, or design work. The exact combination of fonts on your system is surprisingly unique and can be used to identify you across websites without cookies. For the strategic overview of how font fingerprinting fits with other techniques, see our complete browser fingerprinting guide.

How Font Detection Works in the Browser

There are two main methods for detecting installed fonts. The first uses the CSS font fallback mechanism — by measuring the rendered width of text in different fonts, JavaScript can determine whether each font is installed. The second uses the Canvas API to draw text in different fonts and measure the pixel output.

Why Your Font List Is Unique

Most users have their OS default fonts plus fonts installed by specific applications: design software like Adobe Creative Suite installs dozens of unique fonts, development environments install monospace fonts, language packs add regional scripts. A user with Adobe Photoshop installed has a completely different font profile from someone who has only the default Windows fonts.

Protection Against Font Fingerprinting

Brave browser limits font API access and randomizes font fingerprinting. Firefox with privacy.resistFingerprinting reports a reduced, standardized set of fonts. The Tor Browser allows access only to a small, fixed set of fonts to prevent enumeration.

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