Responsive image markup on Wix sites

Sites with srcset and sizes responsive image markup have a good LCP most often: 92%, against 92% of all Wix sites. Sites with <picture> art direction responsive markup have it least often, at 89%.

Fixed-source <img> is the most used: 91.1% of Wix sites. Srcset and sizes is 91.0% of Wix sites.

Across the four LCP sub-parts in Chrome's field data, the largest gap between srcset and sizes and <picture> art direction sits in resource load delay: 471 ms median for srcset and sizes against 502 ms for <picture> art direction. Overall median field LCP is 1.2s for srcset and sizes (TTFB 362 ms, load delay 471 ms, load duration 257 ms, render delay 139 ms) versus 1.3s for <picture> art direction.

React sets the responsive image markup to srcset and sizes on 91% of its sites, and 92% of React sites have a good LCP, against 92% of all sites.

FrameworkResponsive image markup on its sitesGood LCP

Wix sites with responsive image markup 5,599 sitesFixed-source <img> (no srcset) 91%<img srcset="..."> 91%<picture> with <source> 38%92%

React 5,598 sitesFixed-source <img> (no srcset) 91%<img srcset="..."> 91%<picture> with <source> 38%92%

Fixed-source <img> (no srcset) <img srcset="..."> <picture> with <source>

Does the framework explain the responsive image markup difference?

Almost every site with srcset and sizes responsive image markup is a React site, and almost every React site has srcset and sizes responsive image markup, so the data can't tell srcset and sizes responsive image markup and React apart.

How srcset and <picture> select candidate URLs during preload scanning

Chromium's preload scanner evaluates <source media="..." type="..."> and <img srcset="..." sizes="..."> before the main parser builds the DOM. Sites that serve responsive <picture> elements (37.5% of sites) achieve 89% good LCP (1.2s median LCP), compared with 92% on sites using <img srcset> (91.0%) and 92% across sites with fixed-source images (91.1%).