In more detail
Google introduced Web Vitals to give site owners a small set of user-centred measures. The three Core Web Vitals, and the thresholds Google describes as "good" in its web.dev documentation, are:
| Metric | Measures | Good |
|---|---|---|
| Largest Contentful Paint (LCP) | How quickly the main content loads | 2.5 seconds or less |
| Interaction to Next Paint (INP) | How quickly the page responds to interactions | 200 milliseconds or less |
| Cumulative Layout Shift (CLS) | How much the layout jumps around | 0.1 or less |
Google assesses these at the 75th percentile of page loads, split by mobile and desktop. INP replaced First Input Delay as a Core Web Vital in March 2024 (announcement).
Field data comes from real Chrome users and appears in Search Console's Core Web Vitals report and in PageSpeed Insights. Lab tools such as Lighthouse give a simulated score that's useful for debugging but isn't the same as field data.
Google's Core Web Vitals page says it recommends good Core Web Vitals for success in Search and as part of a good page experience, while stressing that relevance and helpful content still matter most.
Why it matters when hiring an agency
Speed work can absorb a lot of budget, so ask an agency to prioritise. Fixing templates that fail on key pages for mobile users makes sense; chasing a perfect lab score on every page rarely does. Ask whether they will implement fixes or hand specifications to your developers, and how they'll measure the result in field data over the following weeks.