Blog
Core Web Vitals and third-party scripts: CORS, fetch priority, and main-thread cost
Third-party SDKs that call cross-origin APIs can delay LCP if they contend for the network during hero rendering.
1 min read
performancecwvcors
Field data
CrUX aggregates real users; lab tests alone miss CORS failures that only happen for certain geographies.
Segment INP regressions by script domain to find the worst contributors.
Privacy
Consent banners affect which third parties load—align RUM sampling with CMP decisions.
Avoid synchronous document.write tags that block parsing before CORS even matters.