At a glance the headline numbers for ETag present
Whether responses carry ETag validators.
87.6% of sites serve ETag validators.
ETag present sites that have it vs sites that don't
87.6% of sites send ETag headers (83,122 of 94,910). With send: LCP 1.4s, 86.1% pass. Without: LCP 1.2s, 87.2% pass. Correlates with +148ms LCP and −1.1 pp pass rate. computed
Why this matters for the Core Web Vitals, and where to start fixing it
An ETag is a validator. When a cached file expires, the browser can ask the server whether it changed and get a tiny 304 Not Modified back instead of the whole file. Without a validator, an expired file is downloaded again in full.
Validators matter most for the in-between caching strategies: short TTLs with frequent revisits. For hashed, immutable assets they are redundant because the file never changes under its name. One thing to watch on multi-server setups: default ETags can differ per server, and a mismatched ETag silently turns every revalidation into a full download.
How does this affect the Core Web Vitals?
Having it makes no measurable difference to the LCP: 86% pass with it, 87% without.
Chrome field data from 94,910 sites, representing millions of real page loads. How we measured.