1
At a glance the headline numbers for Last-Modified present
Whether responses carry Last-Modified validators.
0.0%
Adoption
0 of 0
—
With (median LCP)
—
Without (median LCP)
The State of Web Vitals · Q2 2026 · 189,915 sites · all devices field datacorewebvitals.io/state-of-cwv
2
Last-Modified present sites that have it vs sites that don't
0.0% of sites send Last-Modified headers (0 of 0). With send: LCP —, 0.0% pass. Without: LCP —, 0.0% pass. computed
The State of Web Vitals · Q2 2026 · 189,915 sites · all devices field datacorewebvitals.io/state-of-cwv
3
Why this matters for the Core Web Vitals, and where to start fixing it
Last-Modified is the older validator. The browser sends the timestamp back (If-Modified-Since) and the server answers 304 Not Modified when nothing changed, saving the re-download of an expired cache entry.
It is weaker than an ETag: one-second resolution, and deploys often touch timestamps without changing content, which breaks the match. But any validator beats none. A response with no validator and a short TTL is re-downloaded in full on every revisit.
Go fix it TTFB: cache duration →
Related signals HTTP protocol → HTML size (kB) → Connection hints → HTML compression → Chrome field data from 189,915 sites, representing millions of real page loads · How we measured
Chrome field data from 189,915 sites, representing millions of real page loads. How we measured.