SEO & Performance
Core Web Vitals Optimization
Core Web Vitals — Largest Contentful Paint, Cumulative Layout Shift, and Interaction to Next Paint — measure real user-perceived speed and are used by Google as a ranking signal. Fixing them means finding the specific element or script actually causing the problem, not applying generic 'make it faster' advice.
I diagnose using both lab data (Lighthouse) and field data (real user metrics from Search Console or a monitoring tool), since the two don't always agree and the field data reflects what actual visitors experience.
What Each Metric Actually Measures
- arrow_rightLCP (Largest Contentful Paint) — how long until the largest visible element (usually a hero image or heading) renders
- arrow_rightCLS (Cumulative Layout Shift) — how much visible content shifts unexpectedly during load
- arrow_rightINP (Interaction to Next Paint) — how responsive the page feels when a user actually interacts with it
Common Fixes
- checkOptimizing and correctly sizing the largest above-the-fold image (biggest lever for LCP on most sites)
- checkReserving space for images and ads before they load, to prevent layout shift
- checkSelf-hosting fonts with next/font or equivalent to avoid font-swap layout shift
- checkDeferring non-critical JavaScript that blocks the main thread
- checkReducing the size and priority of render-blocking resources
Frequently Asked Questions
Do Core Web Vitals really affect rankings?add
They're one signal among many in Google's ranking system, more likely to matter as a tiebreaker between otherwise similar-quality pages than as a dominant factor on their own — but they directly affect bounce rate and conversion regardless of their ranking weight, which makes them worth fixing either way.
Why do lab and field data disagree?add
Lab data (Lighthouse) tests a single simulated run under controlled conditions; field data aggregates real visitors on real devices and connections, which vary far more — a site can score well in Lighthouse but poorly in the field if a large share of real visitors are on slow mobile connections.
What's the single biggest lever for LCP?add
On most content sites, it's the largest above-the-fold image — serving it at the correct size, in a modern format, with high loading priority, usually moves LCP more than any other single change.