What is Core Web Vitals?
Core Web Vitals are Google's three measured page-experience metrics: Largest Contentful Paint (loading speed), Interaction to Next Paint (responsiveness) and Cumulative Layout Shift (visual stability), all assessed on real visits, mostly mobile.
Also called: LCP, INP, CLS, page speed metrics.
They are a modest ranking factor and a serious conversion factor. A page taking four seconds on a phone in a patchy signal area loses a meaningful share of visitors before they see anything, and no amount of keyword work recovers those.
Most small business sites fail on the same three causes: enormous unoptimised images, a pile of third-party scripts for chat, analytics and popups, and layout that jumps as fonts and adverts load. Fixing images alone usually moves LCP more than any other single change.
Measure on real mobile data, not a desktop lab score. Field data in Search Console tells you what your customers actually experienced; a laptop on office wi-fi tells you very little.
What to actually do about it
- Serve images in WebP or AVIF, sized for the slot they fill.
- Set explicit width and height on every image to stop layout shift.
- Lazy-load anything below the fold; never lazy-load the hero.
- Audit third-party scripts and delete the ones nobody uses.
- Watch the field data in Search Console, not just Lighthouse.
Koo sites are server-rendered with images converted, resized and lazy-loaded automatically, fonts self-hosted, and no third-party tag manager, so good vitals are the default state rather than a project.
Related terms
Alt text
Alt text is a short written description of an image in its alt attribute, read aloud by screen readers, shown when an image fails to load, and used by search engines to understand what the image shows.
Answer engine optimisation (AEO)
Answer engine optimisation (AEO) is the practice of structuring a website so AI assistants like ChatGPT, Perplexity, Gemini and Google's AI Overviews can quote it accurately when someone asks a question.