How do you optimize custom fonts for fast contentful paint (FCP)?

Optimizing custom fonts for fast contentful paint (FCP) is crucial for improving the perceived loading speed of your web page. Here are several strategies to achieve this:

1. **Use Font Subsetting**: Subsetting involves including only the characters used on a web page in the font files. By reducing the font file size, you can improve loading times. Tools like Font Squirrel or Fontello can help generate subsetted font files based on your requirements.

2. **Preload Fonts**: Use the `preload` directive to instruct the browser to fetch font files early in the page loading process. This ensures that fonts are available when needed, reducing the likelihood of render-blocking delays.

```html
<link rel="preload" href="yourfont.woff2" as="font" type="font/woff2" crossorigin>
```

3. **Use Font Display Swap**: The `font-display: swap;` CSS property ensures that text is displayed using a system font until the custom font is downloaded. This prevents the "flash of invisible text" (FOIT) and improves perceived performance.

```css
@font-face {
  font-family: 'YourFont';
  src: url('yourfont.woff2') format('woff2');
  font-display: swap;
}
```

4. **Optimize Font Formats**: Use modern font formats like WOFF2, which offer better compression and faster loading times compared to older formats like TTF or OTF. Convert your fonts to WOFF2 format to reduce file size and improve loading speed.

5. **Minimize Font Variants**: Include only the necessary font weights and styles in your font files to reduce their size. Avoid including unnecessary font variants that aren't used on your web page.

6. **Cache Fonts**: Leverage browser caching mechanisms and Content Delivery Networks (CDNs) to cache font files. This reduces the need for repeated downloads, improving subsequent page loads.

7. **Serve Fonts Efficiently**: Optimize your server's configuration to serve font files with HTTP compression and caching headers set appropriately. Use tools like Google PageSpeed Insights or Lighthouse to identify opportunities for server-side optimization.

8. **Prioritize Critical Fonts**: Identify the most critical fonts for rendering above-the-fold content and prioritize their loading. Use the `font-display` property with the `optional` or `fallback` value for non-critical fonts to prevent them from delaying FCP.

By implementing these strategies, you can optimize custom fonts for fast contentful paint (FCP), improving the perceived loading speed and user experience of your web pages.