Subresource compression algorithms on React sites

Sites with Brotli compression subresource HTTP compression have a good LCP most often: 86%, against 85% of all React sites. Sites with Zstandard (zstd) compression subresource compression have it least often, at 77%.

Unencoded binary assets is the most used: 99.9% of React sites. Brotli compression is 91.1% of React 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): 496 ms median for Brotli compression against 692 ms for Zstandard (zstd) compression. Overall median field LCP is 1.4s for Brotli compression (TTFB 496 ms, load delay 445 ms, load duration 145 ms, render delay 172 ms) versus 1.7s for Zstandard (zstd) compression.

Wix sets the subresource HTTP compression to Brotli compression on 100% of its sites, and 94% of Wix sites have a good LCP, against 85% of all sites. WordPress sets the subresource HTTP compression to unencoded binary assets on 100% of its sites, and 61% of WordPress sites have a good LCP.

PlatformSubresource HTTP compression on its sitesGood LCP

All React sites 9,570 sitesUnencoded binary assets (images / WOFF2) 100%Gzip (Content-Encoding: gzip) 98%Brotli (Content-Encoding: br) 91%Zstandard (Content-Encoding: zstd) 41%85%

Wix 5,824 sitesBrotli (Content-Encoding: br) 100%Gzip (Content-Encoding: gzip) 100%Unencoded binary assets (images / WOFF2) 100%Zstandard (Content-Encoding: zstd) 32%94%

WordPress 2,342 sitesUnencoded binary assets (images / WOFF2) 100%Gzip (Content-Encoding: gzip) 93%Brotli (Content-Encoding: br) 80%Zstandard (Content-Encoding: zstd) 60%61%

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

Does the platform explain the subresource HTTP compression difference?

On Wix, 94% of sites with Brotli compression subresource HTTP compression have a good LCP, against 94% of Wix sites with unencoded binary assets. Within Wix, sites with Brotli compression and unencoded binary assets have a good LCP about equally often. On WordPress, 61% of sites with Brotli compression subresource HTTP compression have a good LCP, against 61% of WordPress sites with unencoded binary assets. Within WordPress, sites with Brotli compression and unencoded binary assets have a good LCP about equally often.

Brotli, Zstandard (zstd), and Dictionary-Compressed Brotli (dcb) across page subresources

Nearly every page (99.9%) transfers pre-compressed binary formats like WebP, AVIF, and WOFF2 without extra Content-Encoding. For text subresources (JS, CSS, SVG, JSON), 97.7% of sites use Gzip (85% good LCP, 1.4s median), 91.1% use Brotli (86% good LCP), 41.3% include Zstandard responses (77% good LCP, often from Meta/Google third-party scripts), and 0.5% (47 sites, led by Shopify/Cloudflare) use shared-dictionary Brotli (dcb) to achieve 95% good LCP (1.3s median).