How Can the Proper Implementation of Font Display Settings in CSS, Such as Font-Display: Swap;, Minimize Layout Shifts and Improve SEO Through Better Core Web Vitals Scores?


Implementing proper font display settings in CSS, such as font-display: swap;, minimizes layout shifts and improves SEO by enhancing Core Web Vitals scores, particularly the Cumulative Layout Shift (CLS) metric. Here is a detailed explanation of how and why this works.

Core Web Vitals and Their Impact on SEO

Core Web Vitals, introduced by Google, are a set of metrics used to measure the user experience of a web page. They include three main components:

  • Largest Contentful Paint (LCP): Measures loading performance.
  • First Input Delay (FID): Measures interactivity.
  • Cumulative Layout Shift (CLS): Measures visual stability.

Improving these metrics can significantly boost your site's SEO ranking as Google factors them into its search algorithm. To learn more, see [Core Web Vitals, 2023].

Understanding font-display: swap;

The font-display property in CSS controls how web fonts are rendered by the browser. When set to swap, it tells the browser to use a fallback font until the custom web font has fully downloaded, which prevents invisible text (FOIT - Flash of Invisible Text).

Example of using font-display: swap;:

@font-face {
  font-family: 'CustomFont';
  src: url('customfont.woff2') format('woff2');
  font-display: swap;

For more details, visit [MDN Web Docs: font-display, 2023].

Minimizing Layout Shifts

How Layout Shifts Affect User Experience

Layout shifts occur when visible elements move from their initial positions, which can be highly disruptive. This impacts the CLS score, which measures the sum of all unexpected layout shifts that occur during the lifespan of a page.

Using font-display: swap; helps by ensuring that text is immediately rendered with a fallback font, reducing the chance of a layout jump once the custom font loads.

For further reading on CLS, see [Cumulative Layout Shift, 2023].

Practical Benefits

Here’s how font-display: swap; minimizes layout shifts:

  • Fallback Fonts: Users see text in a fallback font if the custom font is still loading, maintaining text visibility.
  • Reduced CLS: Prevents the shift that often occurs when swapping from invisible text to custom fonts, hence lowering your CLS score.

Improving SEO through Better Core Web Vitals Scores

The Importance of CLS in SEO

CLS plays a crucial role in user experience and SEO. Sites with low CLS scores generally provide a better user experience, leading to higher engagement and lower bounce rates. As Google uses user experience as a ranking factor, a better CLS score can directly improve search rankings.

To understand the correlation between Core Web Vitals and SEO, refer to [Evaluating Page Experience, 2020].

Example Implementation

Consider a page using custom fonts without font-display. Users might see blank spaces where text should be until the fonts load, causing a shift once they do. Here's a comparative example:

/* Without font-display: swap */
@font-face {
  font-family: 'CustomFont';
  src: url('customfont.woff2') format('woff2');
/* With font-display: swap */
@font-face {
  font-family: 'CustomFont';
  src: url('customfont.woff2') format('woff2');
  font-display: swap;

Additional Tips

Besides using font-display: swap;, consider these practices:

  • Preconnect: Use <link rel="preconnect" href="" crossorigin> to make early connections to the font provider. See [Preconnect, 2022].
  • Subset Fonts: Load only the required subsets or characters of a font to reduce the overall load time. Detailed guides are available at [Web Font Best Practices, 2022].


Implementing font-display: swap; is a straightforward yet powerful technique to enhance user experience by reducing layout shifts and improving Core Web Vitals scores, particularly CLS. This not only assists in better SEO rankings but also provides a smoother visual experience for visitors.