Connection hints
dns-prefetch, preconnect and preload links the document declares.
At a glance the headline numbers for Connection hints
dns-prefetch, preconnect and preload links the document declares.
Distribution & median LCP site count and median LCP at each level of connection hints — dns prefetch
Passing LCP by connection hints — dns prefetch which level passes the LCP most often
Connection hints — dns prefetch 0. p75 1. p99 8. At the low end (0–0): LCP 1.3s. At the high end (2+): LCP 1.6s. computed
Connection hints — preconnect the value at each percentile across all sites
Connection hints — preconnect 0. p75 1. p99 6. computed
Why this matters for the Core Web Vitals, and where to start fixing it
Hints move network work earlier. dns-prefetch resolves a domain name before it is needed. preconnect goes further and completes the TCP and TLS setup too. preload fetches one specific file that the scanner would otherwise find late, like a background hero image or a critical font.
Hints are easy to overuse. Every preconnect spends sockets and CPU on a connection you might never use. A preload that is not critical steals bandwidth from something that is. A handful of deliberate hints beats a wall of them.
How does this affect the Core Web Vitals?
Connection hints correlate with the LCP. Dns-prefetch hints separates passing sites from failing sites more than preconnect hints does. With few dns-prefetch hints, 89% of sites pass the LCP. With many, 79% do. The decline is gradual. There is no point where sites suddenly start failing.
Chrome field data from 189,915 sites, representing millions of real page loads. How we measured.