WordPress HTTP ETag cache validators and the Core Web Vitals

Sites with ETag validators ETag cache validation have a good LCP most often: 76%, against 76% of all WordPress sites.

Nine in ten WordPress sites uses ETag cache validation, and 100% of those use ETag validators.

Across the four LCP sub-parts in Chrome's field data, the largest gap between ETag validators and no ETag header sits in time to first byte (TTFB): 1004 ms median for ETag validators against 936 ms for no ETag header. Overall median field LCP is 1.8s for ETag validators (TTFB 1004 ms, load delay 290 ms, load duration 128 ms, render delay 220 ms) versus 1.6s for no ETag header.

Alpine sets the ETag cache validation to ETag validators on 96% of its sites, and 82% of Alpine sites have a good LCP, against 76% of all sites.

FrameworkETag cache validation on its sitesGood LCP

All WordPress sites 63,295 sitesETag header present 88%No ETag header 12%76%

Alpine 380 sitesETag header present 96%82%

jQuery 60,314 sitesETag header present 88%No ETag header 12%75%

Vue 4,844 sitesETag header present 84%No ETag header 16%75%

React 2,233 sitesETag header present 89%No ETag header 11%66%

ETag header present No ETag header

Does the framework explain the ETag cache validation difference?

On jQuery, 75% of sites with ETag validators ETag cache validation have a good LCP, against 79% of jQuery sites without ETag cache validation. Within jQuery, sites with ETag validators ETag cache validation have a good LCP less often.

Why ETag headers matter on repeat visits and CDN edge revalidations

An Entity Tag (ETag) is an opaque version identifier attached to an HTTP response. Across 55,531 audited sites (87.7%) that emit ETag headers, browsers and CDN edges can send If-None-Match conditional requests when cached files expire and receive a header-only 304 Not Modified response instead of re-downloading the full payload. Because first-visit crawl and field LCP measurements weight initial loads and immutable hashed assets heavily, sites with ETag headers record 76% good LCP (1.8s median, 1004 ms TTFB) while the 12.3% without ETag headers record 79% good LCP (1.6s median, 936 ms TTFB).