How do you optimize custom fonts for fast paint times (FP)?

Optimizing custom fonts for fast paint times (FP) is crucial for improving the perceived loading speed and visual performance of your web pages. Here are some strategies to optimize custom fonts for fast paint times:

1. **Subset Fonts**: Subset your custom fonts to include only the characters used on a particular web page. By reducing the font file size, you can improve loading times, especially for pages with large amounts of text content.

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. **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.

4. **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;
   }
   ```

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 FP.

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