Font Loading Optimization Implementation

Following our best practices audit, Priority 3 was optimizing font loading to improve performance and reduce Cumulative Layout Shift (CLS). Here’s how we implemented font optimization strategies.

Font Loading Challenges

Our site uses multiple font families:

• Newsreader Variable - Serif headers with optical sizing
• IBM Plex Sans - Body text across multiple weights
• IBM Plex Serif - Alternative serif option
• IBM Plex Mono - Code blocks and technical content

With fonts loaded via @fontsource, they’re bundled by Vite with hashed filenames, making traditional preload strategies challenging.

Implementation Strategy

1. Preconnect to Font Origins

Added preconnect hints to speed up font loading:

<!--Preconnect to speed up font loading-->
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
<!--DNS prefetch as fallback for browsers that don't support preconnect-->
<link rel="dns-prefetch" href="https://fonts.gstatic.com" />

2. Critical Font Face Declarations

Inline critical font-face declarations to minimize Flash of Unstyled Text (FOUT):

<style>
  /* Preload critical font faces to minimize FOUT */
  @font-face {
  font-family: 'Newsreader';
  font-weight: 200 800;
  font-display: swap;
  src: local('Newsreader Variable');
  }
  @font-face {
  font-family: 'IBM Plex Sans';
  font-weight: 400;
  font-display: swap;
  src: local('IBM Plex Sans Regular');
  }
</style>

3. Font Loading Best Practices

Font Display Strategy

Using font-display: swap ensures:

• Text remains visible during font load (no FOIT)
• Graceful swap when custom fonts arrive
• Better perceived performance

Local Font Fallbacks

The src: local() directive allows:

• Instant loading if user has fonts installed
• Zero network requests for some users
• Fallback to web fonts if not available locally

Performance Impact

Before Optimization

• Potential FOUT on slow connections
• No optimization hints for font loading
• Render-blocking font requests

After Optimization

• Faster font connection establishment
• Reduced time to first paint
• Better CLS scores with font-display: swap
• Progressive enhancement with local fonts

Technical Details

Vite Bundle Integration

Since @fontsource fonts are bundled by Vite:

• Font files get hashed names (e.g., newsreader-latin-wght-normal.CCVVNp6i.woff2)
• Traditional preload with exact paths isn’t feasible
• Our approach works around this limitation

Critical CSS Inlining

By inlining critical font-face rules:

• Browser knows about fonts immediately
• Can make better loading decisions
• Reduces render-blocking CSS

Future Enhancements

1. Resource Hints API: Use Astro’s resource hints for automatic preloading
2. Font Subsetting: Create custom subsets for critical text
3. Variable Font Optimization: Load only needed weight ranges
4. Service Worker: Cache fonts for offline use

Monitoring Performance

To verify improvements:

# Run Lighthouse CI
npx lighthouse https://yoursite.com--view
 
# Check specific metrics
- First Contentful Paint (FCP)
- Cumulative Layout Shift (CLS)
- Font load timing in Network tab

Conclusion

Font optimization is crucial for typography-focused sites. Our implementation balances performance with maintainability, ensuring beautiful typography doesn’t come at the cost of user experience.

Next up: Priority 4 - Adding TypeScript prop interfaces to components for better type safety.