Core Web Vitals

Why it matters

They are a direct, if modest, ranking factor in Google search, and more importantly they correlate strongly with whether a visitor actually stays on a page or leaves. A page that scores badly on these metrics is losing both search visibility and real visitors, independent of how good its content is. It also matters for paid acquisition: a slow-loading landing page increases the cost of every click a business is already paying for, since a share of visitors abandon before the page even finishes rendering. It also affects how search engines themselves prioritise crawling a site, since a slow-responding server can reduce how much of a large site actually gets crawled and indexed at all.

What goes wrong when it's handled badly

Sites commonly optimise for a Lighthouse score in a lab test while ignoring field data, what real visitors on real, often slower, connections and devices actually experience, which is what Core Web Vitals in Search Console actually measures. A site that looks fast on a developer's fibre connection and fast test device can still fail Core Web Vitals for the actual visitor base using it on a mid-range phone over mobile data. A concrete example is a site scoring well in a Lighthouse test run once from a fast office connection, while Search Console's real-world field data shows most actual visitors, on 4G in normal conditions, experiencing a materially worse result. Testing against throttled, simulated mobile conditions during development, not just a fast desktop connection, is what actually catches this gap before real visitors do. Monitoring these scores continuously rather than only at launch is what catches a regression introduced by a later, unrelated change.