HTTP ETag cache validators and the Core Web Vitals

Sites with ETag validators ETag cache validation have a good LCP most often: 86%, against 86% of all sites.

83.8% of sites use 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 resource load delay: 283 ms median for ETag validators against 217 ms for no ETag header. Overall median field LCP is 1.4s for ETag validators (TTFB 575 ms, load delay 283 ms, load duration 112 ms, render delay 196 ms) versus 1.3s for no ETag header.

Wix sets the ETag cache validation to ETag validators on 100% of its sites, and 92% of Wix sites have a good LCP, against 86% of all sites.

PlatformETag cache validation on its sitesGood LCP

All sites 210,902 sitesETag header present 84%No ETag header 16%86%

Shopify 8,573 sitesETag header present 100%97%

Squarespace 2,258 sitesETag header present 100%94%

Drupal 3,296 sitesETag header present 92%93%

Joomla 2,551 sitesETag header present 87%No ETag header 13%93%

Wix 5,825 sitesETag header present 100%92%

Adobe Commerce 1,095 sitesETag header present 98%83%

WordPress 65,509 sitesETag header present 88%No ETag header 12%76%

ETag header present No ETag header

Does the platform explain the ETag cache validation difference?

On WordPress, 75% of sites with ETag validators ETag cache validation have a good LCP, against 79% of WordPress sites without ETag cache validation. Within WordPress, 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 176,769 audited sites (83.8%) 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 86% good LCP (1.4s median, 575 ms TTFB) while the 16.2% without ETag headers record 87% good LCP (1.2s median, 549 ms TTFB).