Font Leak Tester: Privacy Check

Find out which system fonts your browser is revealing. Websites use your font list to create a unique fingerprint that tracks you without cookies.

AI Overview

A Font Leak Tester identifies the fonts installed on your computer. Websites use CSS font introspection to measure text widths; if a specific font's width is detected, they know it is on your system. This unique font combination acts as a digital ID, enabling cross-site tracking even if you use a VPN.

What is Font Fingerprinting?

Font Fingerprinting is a method where websites detect the list of fonts installed on your device. Every OS (Windows, macOS, Linux) and every software suite (like Office or Adobe) adds specific fonts to your library. The resulting unique combination of fonts is so specific that it can identify your browser even if you hide your IP address.

Privacy Fact: Advertisers use font enumeration to build a stateless profile. Since you rarely uninstall fonts, this tracking ID lasts much longer than cookies.

How Websites Leak Your Font List

Trackers use CSS font introspection. They render a string of text with a common "fallback" font and measure its width. They then try to render it with a specific font name (like 'Calibri'). If the pixel width changes, the script knows that font is installed. This process tests hundreds of fonts in less than a second.

How to Stop Font Leaks

On ZKB Tracking, we recommend the following browser settings to minimize your footprint:

  • Firefox: Enable privacy.resistFingerprinting in about:config to report only a standard "safe" list of fonts.
  • Brave Browser: Uses Font Farbling to add random noise to font measurements, breaking the tracking hash.
  • Tor Browser: Restricts all users to a small set of bundled fonts so everyone looks identical.
  • Standard Browsers: Avoid installing niche font packs or design software on your primary private browsing device.

Frequently Asked Questions

Does Incognito mode hide my fonts?
No. Incognito mode only stops your history from being saved. It does not prevent JavaScript from reading your hardware and software font lists.

Can a VPN fix font leaks?
No. A VPN only masks your IP. Font detection happens inside your browser and is not affected by your network connection.

Why do I have so many fonts?
Operating systems come with ~50 fonts. Installing Microsoft Office, Adobe, or Language Packs can push that number over 200, making you more trackable.