font-optimization-reference

Web Font Optimization Reference

Quick reference for web font optimization, loading strategies, and performance best practices.

font-display Strategies

Quick Decision Guide

Strategy	FOIT	FOUT	Use Case
swap	❌	✅	Best for body text (recommended)
block	✅	❌	Icons, critical headings
fallback	Short	✅	Balanced approach
optional	Shortest	✅	Performance-first
auto	Browser	Browser	Not recommended

Implementation

/* RECOMMENDED - Body text */
@font-face {
  font-family: 'Inter';
  src: url('/fonts/inter.woff2') format('woff2');
  font-display: swap;
  font-weight: 400;
  font-style: normal;
}

/* Icons - Prevent layout shift */
@font-face {
  font-family: 'Material Icons';
  src: url('/fonts/material-icons.woff2') format('woff2');
  font-display: block;
}

/* Performance-first */
@font-face {
  font-family: 'Optional Font';
  src: url('/fonts/optional.woff2') format('woff2');
  font-display: optional;
}

WOFF2 Format

Complete Format Cascade

@font-face {
  font-family: 'MyFont';
  src: url('font.woff2') format('woff2'),       /* Modern browsers */
       url('font.woff') format('woff'),         /* Fallback */
       url('font.ttf') format('truetype');      /* Legacy */
  font-display: swap;
}

WOFF2 Only (Modern)

@font-face {
  font-family: 'MyFont';
  src: url('font.woff2') format('woff2');
  font-display: swap;
}

Font Preloading

Critical Fonts

<!-- Preload critical fonts -->
<link
  rel="preload"
  href="/fonts/inter-regular.woff2"
  as="font"
  type="font/woff2"
  crossorigin
/>

Multiple Weights

<link rel="preload" href="/fonts/inter-400.woff2" as="font" type="font/woff2" crossorigin>
<link rel="preload" href="/fonts/inter-700.woff2" as="font" type="font/woff2" crossorigin>

⚠️ Warning: Only preload 1-2 critical fonts to avoid blocking rendering.

Google Fonts Optimization

Method 1: Preconnect (Fastest)

<link rel="preconnect" href="https://fonts.googleapis.com">
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
<link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;700&display=swap" rel="stylesheet">

Method 2: Self-Hosting (Best Performance)

/* Download fonts from google-webfonts-helper.herokuapp.com */
@font-face {
  font-family: 'Inter';
  src: url('/fonts/inter-v12-latin-regular.woff2') format('woff2');
  font-display: swap;
  font-weight: 400;
  unicode-range: U+0000-00FF, U+0131, U+0152-0153;
}

Method 3: Font API with Subsetting

<!-- Only load Latin characters, weights 400 and 700 -->
<link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;700&display=swap&subset=latin" rel="stylesheet">

Variable Fonts

Basic Declaration

@font-face {
  font-family: 'Inter Variable';
  src: url('inter-variable.woff2') format('woff2-variations');
  font-display: swap;
  font-weight: 100 900; /* Range */
}

Usage with font-variation-settings

.text {
  font-family: 'Inter Variable', sans-serif;
  font-weight: 600;
}

.custom {
  font-family: 'Inter Variable';
  font-variation-settings: 'wght' 650, 'slnt' -10;
}

Benefits

• 1 file replaces multiple weights (400, 500, 600, 700, etc.)
• Smaller total size for multi-weight usage
• Smooth transitions between weights

Font Subsetting

Unicode Range Subsetting

/* Latin only */
@font-face {
  font-family: 'Inter';
  src: url('inter-latin.woff2') format('woff2');
  unicode-range: U+0000-00FF, U+0131, U+0152-0153;
}

/* Cyrillic only */
@font-face {
  font-family: 'Inter';
  src: url('inter-cyrillic.woff2') format('woff2');
  unicode-range: U+0400-045F, U+0490-0491, U+04B0-04B1;
}

Tools

• glyphhanger - CLI tool for subsetting
• pyftsubset - FontTools subsetting
• google-webfonts-helper - Pre-subsetted Google Fonts

System Font Stacks

Modern System Stack

body {
  font-family:
    -apple-system, BlinkMacSystemFont,
    'Segoe UI', 'Roboto', 'Oxygen',
    'Ubuntu', 'Cantarell', 'Fira Sans',
    'Helvetica Neue', sans-serif;
}

GitHub Stack

font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Noto Sans", Helvetica, Arial, sans-serif;

Monospace Stack

font-family: ui-monospace, 'Cascadia Code', 'Source Code Pro', Menlo, Consolas, monospace;

Performance Optimization

Size-Adjust Descriptor

@font-face {
  font-family: 'Inter';
  src: url('inter.woff2') format('woff2');
  size-adjust: 105%; /* Adjust to match fallback */
}

Font Loading API

// Check if font is loaded
document.fonts.ready.then(() => {
  console.log('All fonts loaded');
});

// Load specific font
const font = new FontFace('Inter', 'url(/fonts/inter.woff2)');
font.load().then(() => {
  document.fonts.add(font);
});

Best Practices Checklist

✅ DO:

• Use WOFF2 format
• Add font-display: swap for body text
• Preload 1-2 critical fonts only
• Self-host Google Fonts when possible
• Subset fonts to required characters
• Use variable fonts for multiple weights
• Include fallback fonts
• Test on slow connections

❌ DON'T:

• Preload all fonts
• Use custom fonts for body text without fallback
• Load entire font families (all weights)
• Forget crossorigin on preload
• Skip WOFF2 compression
• Use EOT or SVG formats
• Load fonts from slow CDNs

Core Web Vitals Impact

LCP (Largest Contentful Paint)

• Preload critical fonts to avoid render blocking
• Use system fonts for fastest LCP
• font-display: swap to render text immediately

CLS (Cumulative Layout Shift)

• Use size-adjust to match fallback metrics
• Preload fonts to reduce shift
• font-display: optional for zero shift (but may not load)

FCP (First Contentful Paint)

• System fonts = instant FCP
• Preconnect to font providers
• Limit font weights to 2-3 maximum

Quick Patterns

Pattern 1: Performance-First

<!-- System fonts with optional web font enhancement -->
<style>
  body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  }
</style>

<link rel="preconnect" href="https://fonts.googleapis.com">
<link href="https://fonts.googleapis.com/css2?family=Inter&display=optional" rel="stylesheet">

<style>
  .enhanced {
    font-family: 'Inter', -apple-system, sans-serif;
  }
</style>

Pattern 2: Self-Hosted Production

<!-- Preload critical fonts -->
<link rel="preload" href="/fonts/inter-400.woff2" as="font" type="font/woff2" crossorigin>

<style>
  @font-face {
    font-family: 'Inter';
    src: url('/fonts/inter-400.woff2') format('woff2');
    font-display: swap;
    font-weight: 400;
  }

  @font-face {
    font-family: 'Inter';
    src: url('/fonts/inter-700.woff2') format('woff2');
    font-display: swap;
    font-weight: 700;
  }

  body {
    font-family: 'Inter', -apple-system, sans-serif;
  }
</style>

Pattern 3: Variable Font

<link rel="preload" href="/fonts/inter-variable.woff2" as="font" type="font/woff2" crossorigin>

<style>
  @font-face {
    font-family: 'Inter Variable';
    src: url('/fonts/inter-variable.woff2') format('woff2-variations');
    font-display: swap;
    font-weight: 100 900;
  }

  body {
    font-family: 'Inter Variable', -apple-system, sans-serif;
    font-weight: 400;
  }

  h1 { font-weight: 700; }
  .thin { font-weight: 300; }
</style>

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Use this reference for quick font optimization lookups and performance improvements.