HTTP cache TTL tiers on React sites

Sites with Cache-Control: immutable HTTP cache TTL tiers have a good LCP most often: 90%, against 84% of all React sites. Sites with short-TTL cache tiers have it least often, at 79%.

Unspecified cache is the most used: 99.8% of React sites. Cache-Control: immutable is 70.7% of React sites.

Across the four LCP sub-parts in Chrome's field data, the largest gap between Cache-Control: immutable and short-TTL sits in time to first byte (TTFB): 433 ms median for Cache-Control: immutable against 598 ms for short-TTL. Overall median field LCP is 1.2s for Cache-Control: immutable (TTFB 433 ms, load delay 446 ms, load duration 117 ms, render delay 160 ms) versus 1.6s for short-TTL.

Wix sets the HTTP cache TTL tiers to Cache-Control: immutable on 100% of its sites, and 94% of Wix sites have a good LCP, against 84% of all sites. WordPress sets the HTTP cache TTL tiers to unspecified cache on 100% of its sites, and 63% of WordPress sites have a good LCP.

PlatformHTTP cache TTL tiers on its sitesGood LCP

All React sites 9,570 sitesUnspecified cache lifetime 100%Long TTL (> 30 days) 92%Medium TTL (1 - 30 days) 92%Cache-Control: no-store 90%Cache-Control: no-cache 78%Cache-Control: immutable 71%Short TTL (< 1 day) 60%84%

Wix 5,824 sitesCache-Control: immutable 100%Medium TTL (1 - 30 days) 100%Unspecified cache lifetime 100%Cache-Control: no-store 100%Long TTL (> 30 days) 100%Cache-Control: no-cache 100%Short TTL (< 1 day) 48%94%

WordPress 2,342 sitesUnspecified cache lifetime 100%Long TTL (> 30 days) 84%Medium TTL (1 - 30 days) 82%Short TTL (< 1 day) 76%Cache-Control: no-store 74%Cache-Control: no-cache 43%Cache-Control: immutable 19%63%

Unspecified cache lifetime Long TTL (> 30 days) Medium TTL (1 - 30 days) Cache-Control: no-store Cache-Control: no-cache Cache-Control: immutable Short TTL (< 1 day)

Does the platform explain the HTTP cache TTL tiers difference?

On Wix, 94% of sites with Cache-Control: immutable HTTP cache TTL tiers have a good LCP, against 94% of Wix sites with unspecified cache. Within Wix, sites with Cache-Control: immutable and unspecified cache have a good LCP about equally often. On WordPress, 62% of sites with Cache-Control: immutable HTTP cache TTL tiers have a good LCP, against 63% of WordPress sites with unspecified cache. Within WordPress, sites with Cache-Control: immutable and unspecified cache have a good LCP about equally often.

How Cache-Control: immutable and long TTLs accelerate repeat views

Field Core Web Vitals combine first visits and repeat navigations from Chrome users. Sites that serve content-hashed static bundles with Cache-Control: immutable (70.7% of sites) achieve 90% good field LCP (1.2s median LCP), outperforming sites limited to short TTLs (59.5%, 79% good LCP) or no-store responses (89.8%, 85% good LCP).