Detected Fonts - BrowserTrace Deep Dive

1. Technical Classification

Font Detection JavaScript Client-Side Passive Fingerprinting

Font detection works by testing whether specific fonts are available on your system. The technique operates by:

Baseline Measurement: Measuring text width with a known fallback font
Font Testing: Applying target font and re-measuring text width
Width Comparison: Different widths indicate font is installed
Invisible Process: All testing happens off-screen without user awareness

2. Background & Purpose

Font detection was one of the earliest browser fingerprinting techniques, documented as early as 2008. The number of fonts on a system varies significantly between users and creates a distinctive identifier.

How It Works

JavaScript creates an invisible text element with specific characters
Measures width using generic fallback fonts (serif, sans-serif, monospace)
Tests hundreds of common font names by applying them to the text
If width changes, the font exists on the system
Counts total number of detected fonts

Why Font Count Matters

The number of installed fonts varies based on:

Operating System: macOS includes 200+ fonts, Windows 100+, Linux varies widely
Software Installation: Adobe Creative Suite adds 1000+ fonts
User Customization: Designers and developers install additional fonts
Language Packs: Asian language support adds specialized fonts
System Age: Older systems may have fewer or different fonts

3. Typical Values & What They Reveal

Example Detection Code

function isFontAvailable(fontName) {
    const testString = 'mmmmmmmmmmlli';
    const testSize = '72px';

    const canvas = document.createElement('canvas');
    const ctx = canvas.getContext('2d');

    // Measure with fallback font
    ctx.font = testSize + ' monospace';
    const baseWidth = ctx.measureText(testString).width;

    // Measure with target font
    ctx.font = testSize + ' ' + fontName + ', monospace';
    const testWidth = ctx.measureText(testString).width;

    return baseWidth !== testWidth;
}

Typical Font Counts by Platform

Platform / Configuration	Typical Font Count	What It Reveals
Windows (Default)	100-150 fonts	Standard consumer Windows installation
macOS (Default)	200-300 fonts	Apple includes more fonts by default
Linux (Minimal)	30-80 fonts	Lightweight distribution or server install
Linux (Full Desktop)	100-200 fonts	Ubuntu/Fedora with full desktop environment
Creative Professional	500-2000+ fonts	Adobe Creative Suite or similar installed
Mobile (iOS/Android)	20-50 fonts	Mobile devices have limited font sets

Uniqueness Factor: While font count alone isn't unique, it significantly narrows down possibilities when combined with other fingerprinting data. For example, 1200+ fonts strongly suggests a creative professional on macOS or Windows.

4. Common Uses & Applications

Legitimate Uses

Font Preview: Web design tools checking which fonts to display
Typography Applications: Font managers and design software
Cross-Platform Compatibility: Ensuring documents display correctly
Progressive Enhancement: Using available fonts for better design

Privacy-Invasive Uses

User Profiling: Identifying creative professionals, developers, specific language speakers
Device Fingerprinting: Contributing to unique browser fingerprint
Tracking Without Cookies: Persistent identifier across browsing sessions
Cross-Site Correlation: Linking user activity across different websites

5. Platform & Environment Differences

Operating System Defaults

Windows Font Stack

Windows includes core fonts like Arial, Times New Roman, Courier New, plus system fonts for UI. Professional versions include additional business fonts.

macOS Font Collection

macOS ships with extensive font library including San Francisco (system font), Helvetica, Times, many specialty fonts, and international scripts.

Linux Variability

Highly variable based on distribution. Ubuntu includes Liberation fonts, DejaVu family. Minimal systems may only have basic fonts.

Software-Specific Font Additions

Adobe Creative Cloud: Adds 1000+ fonts including entire Adobe Fonts library
Microsoft Office: Includes Calibri, Cambria, additional professional fonts
Google Fonts Downloaded: Web designers often install Google Fonts locally
Typography Tools: Font managers, design applications add specialty fonts

6. Privacy Implications & Tracking Risks

Privacy Risk: VERY HIGH

Font detection reveals detailed information about your system configuration, installed software, and potentially your profession or interests.

What Font Count Reveals About You

Professional Identity

High font counts (500+) strongly indicate creative professionals, graphic designers, or typography enthusiasts. This information could be used for targeted advertising or price discrimination.

Language & Location

Presence of specific script fonts (Chinese, Arabic, Hebrew, etc.) reveals language capabilities and potential geographic location or cultural background.

Operating System Detection

Font counts help distinguish between Windows, macOS, and Linux, and even specific versions or distributions.

Fingerprinting Power

Persistent Identifier: Font list rarely changes, creating stable tracking ID
Incognito Ineffective: Same fonts detected in private browsing mode
Cross-Browser Tracking: Same fonts detected across different browsers
Combined with Other Data: Dramatically increases fingerprint uniqueness

Real-World Privacy Concerns

Advertising Networks

Ad networks use font detection as part of device fingerprinting to track users who delete cookies or use ad blockers.

Corporate Espionage

Competitors could identify employees of specific companies based on proprietary corporate fonts installed on work devices.

7. Protection & Mitigation

Browser-Based Protections

Tor Browser (Most Effective)

Method: Reports only a limited set of standard fonts

Effectiveness: High - all Tor users appear identical

Tradeoff: Some websites may display incorrectly

Firefox Privacy Settings

Method: privacy.resistFingerprinting limits font enumeration

Enable: Type about:config, set privacy.resistFingerprinting = true

Effectiveness: Moderate - reduces but doesn't eliminate detection

Brave Browser

Method: Blocks or limits font enumeration techniques

Effectiveness: Moderate-High depending on shield settings

Browser Extensions

Canvas Blocker (Firefox): Can block font enumeration attempts
Privacy Badger: Learns to block fingerprinting scripts
NoScript: Blocks all JavaScript (breaks many sites)

Manual Protection Strategies

Minimize Installed Fonts: Remove unnecessary fonts (impractical for professionals)
Use Standard Configuration: Avoid installing unusual fonts
Virtual Machine: Use fresh VM for sensitive browsing
Separate Browsers: Use different browsers for different activities

What Doesn't Work

Incognito Mode: Same fonts detected as normal browsing
Clearing Cookies: No effect on font detection
VPN: Changes IP but not system fonts
Ad Blockers: Most don't prevent font enumeration

Recommended Approach: Use Firefox with privacy.resistFingerprinting enabled, or Brave Browser with strict shields. For maximum privacy, use Tor Browser.

8. Learn More

BrowserLeaks Font Detection Test which fonts are detectable on your system EFF Cover Your Tracks Comprehensive fingerprinting test including font detection MDN Web Docs - CSS Fonts Technical documentation on web font handling Wikipedia - Device Fingerprinting Overview of fingerprinting techniques including fonts W3C: Unsanctioned Web Tracking W3C's position on fingerprinting techniques Firefox Anti-Fingerprinting Firefox's built-in protections against fingerprinting Brave's Fingerprinting Protection How Brave protects against font fingerprinting Arkenfox User.js Advanced Firefox privacy configuration guide

Detected Fonts Count

Your Detected System Fonts