Core Web Vitals measure three things users feel: how fast the main content appears, how quickly the page responds to a tap, and whether the layout jumps around. Google measures them at the 75th percentile of real page loads, separately for mobile and desktop, and a page passes only if it meets all three.
LCP: get the main content on screen
Largest Contentful Paint is usually the hero image or headline. Most slow LCP comes from a slow server response, a render-blocking stylesheet or font, or an oversized hero image that loads late.
- Serve modern formats (WebP or AVIF) sized for the slot
- Preload the hero image and main font
- Never lazy-load the LCP image
- Cache HTML at the edge for marketing pages
INP: respond to every tap quickly
Interaction to Next Paint became a stable Core Web Vital in 2024, replacing First Input Delay. It looks at responsiveness across the whole visit, so heavy scripts that block the main thread hurt it.
- Remove or delay third-party scripts you do not need on load
- Break long tasks into smaller chunks
- Avoid huge DOM updates on each keystroke
- Load chat widgets and tag managers after interaction where possible
CLS: stop the page from jumping
Layout shift comes from images, ads, embeds and banners that load without reserved space, and from web fonts swapping in with different sizes.
- Set width and height on every image and video
- Reserve space for banners and embeds
- Use font-display and matched fallback fonts
- Do not insert content above what the user is reading
Measure real users, not just lab tests
Lab tools are good for debugging, but the pass or fail comes from real visits. Use Search Console's Core Web Vitals report and field data to see which groups of URLs fail, then fix templates rather than single pages.
XDQ Labs builds marketing sites as static or server-rendered pages for this reason: the content arrives in the first response, which helps both Core Web Vitals and AI crawlers that read raw HTML.
Frequently asked questions
What are good Core Web Vitals scores?
LCP of 2.5 seconds or less, INP of 200 milliseconds or less and CLS of 0.1 or less, at the 75th percentile of page loads.
When did INP replace FID?
Interaction to Next Paint became a stable Core Web Vital in 2024, replacing First Input Delay.
Do Core Web Vitals affect rankings?
They are part of Google's page experience signals. They rarely beat relevance, but slow pages lose visitors whatever their ranking.
Why do lab and field scores differ?
Lab tests run one simulated load on one device. Field data reflects real users on many devices and networks, which is what Google uses to judge Core Web Vitals.
Sources
- Web Vitals, web.dev (Google), 2026
