Blog
dns-prefetch and preconnect: faster connections to API origins that still require CORS
Hints warm DNS and TLS but do not grant cross-origin permission—fetch still needs proper CORS headers.
1 min read
performancehtmlcors
Measurement
Compare LCP and TTFB on API-heavy SPAs with and without preconnect using real user monitoring.
Too many preconnects can waste socket limits—prioritize the critical API host only.
HTTP/3
QUIC connection IDs change behavior; validate preconnect hints across HTTP versions your CDN supports.
Alt-Svc headers may shift hosts—keep hints aligned with actual request URLs.