You get Core Web Vitals data from three main sources, each serving different purposes. Google Search Console provides the most important view because it shows real user metrics (field data) collected from actual Chrome users visiting your site over the past 28 days. Navigate to Experience > Core Web Vitals to see which URLs pass or fail for mobile and desktop. This is what Google uses for ranking, so it's your primary reference. PageSpeed Insights combines both field data and lab data when you test a specific URL. Enter any page, and you'll see real user metrics at the top (if enough Chrome users have visited) plus simulated performance scores below. The lab data helps diagnose issues but doesn't directly affect rankings. Use this for detailed optimization work on individual templates. Chrome DevTools Lighthouse runs purely simulated tests in controlled conditions. Press F12 in Chrome, go to the Lighthouse tab, and generate a report. This is useful during development because you get instant feedback without waiting for real traffic, but scores often differ from production because lab conditions don't match real networks, devices, or server load. For clients with 500+ domains, we monitor Core Web Vitals through Search Console's API, pulling data weekly to catch regressions early. Small sites under 1,000 monthly visitors may not generate enough Chrome User Experience Report data to appear in Search Console, so you'll rely more on lab testing until traffic grows. The three metrics that matter: LCP (Largest Contentful Paint) should be under 2.5 seconds, CLS (Cumulative Layout Shift) under 0.1, and INP (Interaction to Next Paint) under 200ms. INP replaced FID in March 2024. If Search Console shows failures, prioritize mobile first since most organic traffic comes from phones. Check your hosting response times, image optimization, and render-blocking JavaScript before diving into complex fixes.