Repeated geometry reads after DOM changes can turn a small interaction into expensive rendering work. Learn to identify forced layout, restructure measurement loops, and schedule updates without introducing stale coordinates or delayed feedback.
The CrUX API returns 28-day rolling p75 field data for LCP, INP, CLS, FCP, and TTFB on any origin or URL with enough Chrome traffic. Here's how to query it, read the histograms, and pair it with your RUM without getting lost in the discrepancies.
A practical 2026 guide to document.startViewTransition: baseline support, view-transition-name, class grouping, the types parameter, and INP-safe patterns.
rel=modulepreload fetches, parses, and compiles ES modules ahead of time, populating the module map so import() resolves instantly and LCP drops by hundreds of ms.
How CDN origin shielding raises cache hit ratio and cuts origin TTFB. Setup for Fastly, Cloudflare, and CloudFront with Cache-Control tips and debug headers.
Move GTM, GA4, and Meta Pixel into a web worker with Partytown. Real INP numbers, framework setup, dataLayer forwarding, and the caveats that break analytics.
The NotRestoredReasons API is how you learn, per real user navigation, why Chrome refused to restore your page from bfcache. Here's the RUM snippet I ship in production, the full 2026 blocker list, and how to fix each one.
Learn how to optimize First Contentful Paint below 1.8s at p75. Covers TTFB reduction, render-blocking CSS, web fonts, 103 Early Hints, and Speculation Rules prerender with production code.
Understand every value of the CSS contain property (layout, paint, size, strict, content) with 2026 browser support notes, DevTools workflow, and real-world INP wins.
How CDN cache tags and surrogate keys work in 2026: headers, purge APIs, and stale-while-revalidate pairing on Fastly, Cloudflare, Vercel, Netlify, and Akamai.
Cross-origin resources report zero for duration, transferSize, and every phase timing unless the server emits Timing-Allow-Origin. Set it correctly on CDN, S3, or your API to unlock full Resource Timing and honest RUM data.
A third-party script facade is a static placeholder that loads no third-party JavaScript until the user interacts with it. In field data, swapping a YouTube iframe for a facade cuts LCP by 40% on mobile 4G. Here is the 2026 pattern for YouTube, Twitter, Maps, and chat widgets.
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