Shopify font-display and the Core Web Vitals

Here, a site counts under every font-display value present in its @font-face rules. Sites with at least one matching rule have a good LCP: swap at 95%, auto at 94%, fallback at 93%, block at 92%. Why does swap (95%) sit right next to auto (94%)? Three in four sites that load Google Fonts with swap also load icon or theme fonts with block or auto. Those multi-font pages count under both values.

Here, a site counts under every font-display value present in its @font-face rules. Sites with at least one matching rule have a good CLS: fallback at 94%, swap at 94%, auto at 93%, block at 90%. Why does swap (94%) sit right next to auto (93%)? Three in four sites that load Google Fonts with swap also load icon or theme fonts with block or auto. Those multi-font pages count under both values.

Across 8,141 Shopify sites that declare web fonts, swap accounts for 71.2% of all @font-face rules, auto for 21.7%, block for 5.4%, fallback for 1.7%, and optional for . At the site level, 60.4% of sites mix swap with blocking rules on the same page, 10.7% use only blocking rules (auto, block, or fallback), and 28.9% use swap or optional on every font rule.

When each site is counted once by its full rule mix, sites that keep every font on swap or optional have a good LCP on 97% of sites, against 94% for blocking-only sites and 94% for mixed sites. Mixed sites load a median of 6 font files across 20 @font-face rules (usually Google Fonts plus Font Awesome or theme icon fonts). Pure swap sites load a median of 4 font files across 7 rules.

When each site is counted once by its full rule mix, sites that keep every font on swap or optional have a good CLS on 96% of sites, against 93% for blocking-only sites and 93% for mixed sites. Mixed sites load a median of 6 font files across 20 @font-face rules (usually Google Fonts plus Font Awesome or theme icon fonts). Pure swap sites load a median of 4 font files across 7 rules.

Comparing sites that load the same number of font files separates font-display from font count. With 1 to 2 font files, sites on pure swap have a good LCP on 98% of sites, against 100% for sites with any block rule. On pages loading 8 or more font files, pure swap reaches 96% against 91% for sites with block.

Comparing sites that load the same number of font files separates font-display from font count. With 1 to 2 font files, sites on pure swap have a good CLS on 97% of sites, against 92% for sites with any block rule. On pages loading 8 or more font files, pure swap reaches 98% against 87% for sites with block. At every font count, pure swap matches or beats block on field CLS.

On jQuery, 65% of declared @font-face rules use font-display: swap, 26% use auto, and 8% use block. 93% of jQuery sites have a good LCP. On Vue, 72% of rules use swap, 25% use auto, and 2% use block, and 94% of Vue sites have a good LCP.

On jQuery, 65% of declared @font-face rules use font-display: swap, 26% use auto, and 8% use block. 91% of jQuery sites have a good CLS. On Vue, 72% of rules use swap, 25% use auto, and 2% use block, and 90% of Vue sites have a good CLS.

Framework@font-face rules on its sitesGood LCP

Shopify sites with font-display 8,141 sitesswap 71%auto (browser default) 22%95%

Vue 931 sitesswap 72%auto (browser default) 25%94%

jQuery 3,121 sitesswap 65%auto (browser default) 26%93%

swap auto (browser default) block fallback optional

Does the framework explain the font-display gap?

On jQuery, 96% of sites that keep every font on swap or optional have a good LCP, compared with 93% for blocking-only sites and 92% for jQuery sites that mix swap with blocking rules. Within jQuery, keeping every font on swap beats mixing rules by 4 percentage points. On Vue, 97% of sites that keep every font on swap or optional have a good LCP, compared with 96% for blocking-only sites and 94% for Vue sites that mix swap with blocking rules. Within Vue, pure swap and mixed sites have a good LCP about equally often.

On jQuery, 93% of sites that keep every font on swap or optional have a good CLS, compared with 92% for blocking-only sites and 90% for jQuery sites that mix swap with blocking rules. Within jQuery, pure swap and mixed sites have a good CLS about equally often. On Vue, 94% of sites that keep every font on swap or optional have a good CLS, compared with 87% for blocking-only sites and 89% for Vue sites that mix swap with blocking rules. Within Vue, pure swap and mixed sites have a good CLS about equally often.

How font-display affects LCP and CLS during page load

When text is the LCP element, font-display: block and font-display: auto hide it for up to 3 seconds while the font file downloads. If the font arrives late, that wait delays LCP directly. With font-display: swap, the browser paints the fallback system font right away so LCP is recorded on first render, then swaps in the web font once it downloads. Swapping an unadjusted fallback font can shift text lines. Even so, pure swap sites match or beat blocking sites on field CLS at every font count (96% good CLS).