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Optimizing Web Fonts for Maximum Performance

Juri Vasylenko
Written by Juri Vasylenko
Denis Pakhaliuk
Reviewed by Denis Pakhaliuk

What You Need to Know About Web Fonts

Why fonts are more than just a design element—they impact site speed and quality?

Web fonts are no longer just decorative elements. Today, they are part of performance infrastructure. The choice of font and how it is loaded directly affects content rendering speed, page visual stability, and even brand perception.

What are web fonts?

These are files (usually in .woff2, .woff, .ttf, etc.) that are loaded from a server when a website is opened, allowing text to be displayed in the designer’s chosen style.

How browsers load fonts?

When rendering a page, the browser reads the CSS, finds @font-face, determines which fonts are needed, and starts loading them. During this process, text may be temporarily hidden (FOIT — Flash of Invisible Text) or replaced with a system font (FOUT — Flash of Unstyled Text).

Why it matters?

Every extra kilobyte and loading delay affects key performance metrics:

  • LCP (Largest Contentful Paint): Time to render the main content of the page
  • CLS (Cumulative Layout Shift): Layout shifts caused by font loading
  • FCP (First Contentful Paint): Time until the first content appears
  • TBT (Total Blocking Time): Total blocking time during page load

Unoptimized fonts can make a site beautiful but slow.

Formats and Modern Standards

From TTF to WOFF2 — choosing the optimal format in 2025

Web once relied on bulky .ttf and .otf fonts, but things have changed. Browsers now support more compressed and efficient formats.

Format comparison:

  • WOFF2: Modern standard, up to 30% better compression than WOFF
  • WOFF: Older format, used as a fallback
  • TTF / OTF: Outdated, suitable only for development or fallback
  • EOT: Relic of the Internet Explorer era, avoid using

What to choose:

Use WOFF2 as the priority and WOFF as a fallback. This ensures compatibility and an optimal balance between speed and visual quality.

How to Speed Up Font Loading?

Secrets to light and fast fonts: from subsetting to preconnect

One of the most underestimated ways to speed up a site is reducing font size.

Why reducing the character set matters

Most fonts contain thousands of glyphs: Latin, Cyrillic, Asian, mathematical symbols, etc. If your site only uses Latin characters, you’re unnecessarily loading hundreds of kilobytes. Solution: Subsetting—trimming the font to the needed Unicode range.

Font loading lifecycle:

  1. Browser finds the font link
  2. Downloads the file (may be deferred)
  3. Applies it to text—possible flicker (FOIT/FOUT)
  4. Caches for future visits

How to avoid FOIT and FOUT

Use font-display: swap; —this shows a system font first, then replaces it with the custom font without a blank screen.

What is Preconnect and DNS Prefetch

If fonts are hosted on an external domain (e.g., Google Fonts), the browser spends time establishing a connection. Example:

<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>

This can save 100–300 ms.

Common preloading mistakes:

  • Duplicate <link rel="preload"> and @font-face paths
  • Missing crossorigin attribute
  • Preloading fonts not used above the fold

Where and How to Host Fonts Correctly?

Self-hosting vs. using a CDN

CDNs like Google Fonts are convenient but not always efficient. Each site visit requires a connection to an external server, slowing loading and potentially raising legal issues (GDPR).

Why avoid Google Fonts CDN

In 2022, German courts ruled that using Google Fonts without consent violates GDPR, as CDN requests transmit the user’s IP address.

Benefits of local hosting:

  • Fewer dependencies on third-party services
  • Full caching control
  • Improved privacy and speed

HTTP font caching strategies:

Set headers:

Cache-Control: public, max-age=31536000, immutable

This allows browsers to cache fonts for up to a year.

Immutable resources

Use versioning via file hash (e.g., inter-v12.woff2?v=abcd1234) to prevent caching issues during updates.

When Fonts Affect Interface Stability

How fonts cause content shifts

When a custom font loads late, text “jumps,” affecting CLS. To prevent this, select fallback fonts with similar metrics.

Metrics alignment to prevent CLS

Use font-size-adjust to match visual size between temporary and final fonts. You can also specify ascent-override, descent-override, and line-gap-override for line height control.

Impact of font loading on critical rendering path

Fonts are render-blocking if loaded incorrectly. Load only fonts needed for visible content; defer the rest.

Key metrics:

  • Font Load Time
  • Blocking Time
  • CLS Impact

How to diagnose problematic fonts:

Use Chrome DevTools → Coverage and Lighthouse → Performance / Font Display. If fonts block rendering or aren’t used, optimize them.

Security and Privacy in the GDPR Era

GDPR issues with Google Fonts

When a browser loads a font from fonts.googleapis.com, it sends the user’s IP address—personal data.

Self-hosting as a solution

Hosting fonts on your domain eliminates external requests and fully resolves privacy concerns.

CORS settings for security

Add to server headers:

Access-Control-Allow-Origin: *

so browsers correctly load fonts from your domain.

Avoid external tracking

Do not use third-party font CDNs. If updates are needed, download new versions manually or automate via CI/CD.

Final Recommendations and Checklist

Font optimization checklist:

  • Use WOFF2 format
  • Set font-display: swap
  • Load fonts via preload
  • Perform subsetting
  • Configure caching
  • Avoid external CDNs

Example of an ideal setup:

@font-face {
font-family: 'Inter';
src: url('/fonts/inter.woff2') format('woff2');
font-display: swap;
}
body {
font-family: 'Inter', system-ui, -apple-system, 'Segoe UI', sans-serif;
}

Common mistakes:

  1. Loading unnecessary fonts on all pages
  2. Using @import instead of
  3. Missing crossorigin during preload

Performance gains after optimization:

  • Page load time reduced by 20–40%
  • CLS reduced to 0.01–0.03
  • Overall page weight reduced by 50–150 KB

Key takeaway:

Font optimization isn’t about aesthetics—it’s about stability and speed. Proper font loading and hosting improve UX and SEO simultaneously.

Final recommendations:

Start simple: WOFF2 + font-display: swap. Then add subsetting, caching, and local hosting. These steps provide real speed improvements without design compromises.

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