Core Web Vitals are three Google-defined performance metrics that measure real-user page experience. They are Largest Contentful Paint (LCP, time to render the largest visible content), Interaction to Next Paint (INP, latency between user input and visual feedback — replaced First Input Delay in 2024), and Cumulative Layout Shift (CLS, visual stability during page load).
The current 2026 targets for "good" performance are LCP under 2.5 seconds, INP under 200 milliseconds, and CLS under 0.1. Google uses these as a ranking signal in both classic search and AI Overviews source candidacy. Pages that fail Core Web Vitals get demoted in ranking even when their content is otherwise strong.
Field data — real measurements from actual visitors via the Chrome User Experience Report (CrUX) — counts more than lab data. Lighthouse scores tell you whether you can pass; CrUX tells you whether you are passing. Optimize against your CrUX numbers, not your Lighthouse simulation.
For AEO specifically, Core Web Vitals also affect AI-bot crawl rate. PerplexityBot and other AI crawlers have tight per-request time budgets — pages with slow TTFB get sampled less frequently and dropped from the index faster when the crawler is rate-limited. A fast site is crawled more, indexed deeper, and cited more often.