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Web Font Performance Tips

Optimize your web fonts to improve loading times, reduce layout shifts, and enhance the user experience.

The Impact of Web Fonts on Performance

Web fonts are essential for creating beautiful, branded typography on the web, but they can significantly impact page load times and user experience if not implemented properly. Each font file is an additional resource that must be downloaded, parsed, and rendered by the browser.

Poor font loading can lead to issues like:

  • Flash of Invisible Text (FOIT) - Text remains invisible until the font loads
  • Flash of Unstyled Text (FOUT) - Text initially displays in a fallback font, then switches
  • Layout shifts - Content jumps as fonts load and text reflows
  • Increased page weight - Large font files can slow down page loading

Optimizing Font Loading

Here are key strategies to improve web font performance:

1. Use Font Preloading

Preloading critical fonts tells the browser to fetch them early in the page load process:

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

Only preload fonts that appear above the fold to avoid wasting bandwidth on resources that aren't immediately needed.

2. Implement Font Display Strategies

The CSS font-display property controls how fonts render before they're loaded:

@font-face {
  font-family: 'My Font';
  src: url('my-font.woff2') format('woff2');
  font-weight: 400;
  font-style: normal;
  font-display: swap; /* or: auto, block, fallback, optional */
}

Common values include:

  • swap - Shows fallback font immediately, swaps when custom font loads (prevents FOIT)
  • optional - Gives font a short block period and fallback if not loaded quickly (good for non-essential fonts)
  • fallback - Short block period, then fallback with swap if loaded within a few seconds

3. Use Modern Font Formats

WOFF2 offers the best compression (30-50% smaller than WOFF):

@font-face {
  font-family: 'My Font';
  src: url('my-font.woff2') format('woff2'),
       url('my-font.woff') format('woff');
  /* Older formats as fallbacks if needed */
}

Reducing Font File Size

1. Subset Fonts

Only include the characters you need. For Latin-based languages, subsetting can reduce file size by 60-80%:

  • Use tools like glyphhanger to analyze and subset fonts
  • For Google Fonts, use the &text= parameter to request only specific characters

2. Limit Font Weights and Styles

Each weight and style is a separate download. Be strategic:

  • For body text, you might need regular, italic, bold, and bold italic
  • For headings, you might only need one or two weights
  • Consider if you really need light, semibold, or other weights

3. Consider Variable Fonts

Variable fonts contain multiple weights and styles in a single file:

  • Can be smaller than loading multiple individual font files
  • Provide access to the entire range of weights and styles
  • Example usage:
@font-face {
  font-family: 'My Variable Font';
  src: url('my-variable-font.woff2') format('woff2-variations');
  font-weight: 100 900; /* Supports the full range */
}

.light-text {
  font-weight: 300;
}

.bold-text {
  font-weight: 700;
}

Hosting and Delivery Optimization

1. Self-Hosting vs. Font Services

Consider the trade-offs:

  • Self-hosting: More control over loading strategies and caching, but requires maintenance
  • Font services (like Google Fonts): Convenient but may have performance implications

If using Google Fonts, implement best practices:

<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">

2. Use Effective Caching

Set appropriate cache headers for font files:

  • Long cache times (1 year) for versioned font files
  • Consider using a content delivery network (CDN) for global distribution

Fallback Font Optimization

Well-matched fallback fonts reduce layout shifts when custom fonts load:

1. Size-Adjust and Metrics Overrides

Modern browsers support properties to match fallback fonts more closely to custom fonts:

@font-face {
  font-family: 'My Font Fallback';
  src: local('Arial');
  size-adjust: 105%;
  ascent-override: 90%;
  descent-override: 25%;
  line-gap-override: 0%;
}

2. Font Style Matcher

Use tools like Font Style Matcher to find fallback font settings that closely match your web font.

Measuring Font Performance

Regularly test your font loading performance:

  • Use Lighthouse in Chrome DevTools to identify font-related issues
  • Monitor Cumulative Layout Shift (CLS) metrics
  • Test on slow connections and mobile devices
  • Use WebPageTest to analyze font loading waterfall

Practical Implementation Example

Here's a comprehensive example combining multiple optimization techniques:

<!-- In the <head> -->
<link rel="preload" href="fonts/my-font-regular.woff2" as="font" type="font/woff2" crossorigin>

<style>
/* Optimized fallback font */
@font-face {
  font-family: 'My Font Fallback';
  src: local('Arial');
  size-adjust: 102%;
  ascent-override: 92%;
  descent-override: 23%;
  line-gap-override: 0%;
}

/* Custom font with display strategy */
@font-face {
  font-family: 'My Font';
  src: url('fonts/my-font-regular.woff2') format('woff2');
  font-weight: 400;
  font-style: normal;
  font-display: swap;
}

/* Variable font for multiple weights */
@font-face {
  font-family: 'My Variable Font';
  src: url('fonts/my-variable-font.woff2') format('woff2-variations');
  font-weight: 100 900;
  font-display: swap;
}

/* Font stack with optimized fallback */
body {
  font-family: 'My Font', 'My Font Fallback', sans-serif;
}

h1, h2, h3 {
  font-family: 'My Variable Font', system-ui, sans-serif;
}
</style>

Further Resources