WordPress subresource compression algorithms and the Core Web Vitals

Sites with Brotli compression subresource HTTP compression have a good LCP most often: 70%, against 70% of all WordPress sites. Sites with Zstandard (zstd) compression subresource compression have it least often, at 67%.

Unencoded binary assets is the most used: 99.9% of WordPress sites. Brotli compression is 72.3% of WordPress sites.

Across the four LCP sub-parts in Chrome's field data, the largest gap between Brotli compression and Zstandard (zstd) compression sits in time to first byte (TTFB): 1102 ms median for Brotli compression against 1177 ms for Zstandard (zstd) compression. Overall median field LCP is 1.9s for Brotli compression (TTFB 1102 ms, load delay 344 ms, load duration 170 ms, render delay 239 ms) versus 2.0s for Zstandard (zstd) compression.

Alpine sets the subresource HTTP compression to Brotli compression on 86% of its sites, and 80% of Alpine sites have a good LCP, against 70% of all sites. jQuery sets the subresource HTTP compression to unencoded binary assets on 100% of its sites, and 69% of jQuery sites have a good LCP.

FrameworkSubresource HTTP compression on its sitesGood LCP

All WordPress sites 63,295 sitesUnencoded binary assets (images / WOFF2) 100%Gzip (Content-Encoding: gzip) 91%Brotli (Content-Encoding: br) 72%Zstandard (Content-Encoding: zstd) 56%70%

Alpine 380 sitesUnencoded binary assets (images / WOFF2) 100%Gzip (Content-Encoding: gzip) 95%Brotli (Content-Encoding: br) 86%Zstandard (Content-Encoding: zstd) 79%80%

jQuery 60,314 sitesUnencoded binary assets (images / WOFF2) 100%Gzip (Content-Encoding: gzip) 92%Brotli (Content-Encoding: br) 72%Zstandard (Content-Encoding: zstd) 57%69%

Vue 4,844 sitesUnencoded binary assets (images / WOFF2) 100%Gzip (Content-Encoding: gzip) 84%Brotli (Content-Encoding: br) 65%Zstandard (Content-Encoding: zstd) 34%68%

React 2,233 sitesUnencoded binary assets (images / WOFF2) 100%Gzip (Content-Encoding: gzip) 93%Brotli (Content-Encoding: br) 80%Zstandard (Content-Encoding: zstd) 61%61%

Unencoded binary assets (images / WOFF2) Gzip (Content-Encoding: gzip) Brotli (Content-Encoding: br) Zstandard (Content-Encoding: zstd)

Does the framework explain the subresource HTTP compression difference?

On jQuery, 69% of sites with Brotli compression subresource HTTP compression have a good LCP, against 69% of jQuery sites with unencoded binary assets. Within jQuery, sites with Brotli compression and unencoded binary assets have a good LCP about equally often. On Vue, 68% of sites with Brotli compression subresource HTTP compression have a good LCP, against 68% of Vue sites with unencoded binary assets. Within Vue, sites with Brotli compression and unencoded binary assets have a good LCP about equally often.