There are three Core Web Vitals that Google uses as official ranking signals. As of March 2024, they are Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS). These replaced the original trio that included First Input Delay (FID) instead of INP. LCP measures loading performance and should occur within 2.5 seconds of when the page first starts loading. It tracks when the largest image or text block becomes visible in the viewport. INP replaced FID in March 2024 and measures overall responsiveness throughout the entire page lifecycle, not just the first interaction. Good INP is under 200 milliseconds. CLS quantifies visual stability by measuring unexpected layout shifts, with a good score being less than 0.1. These three metrics were chosen because they represent the most critical aspects of user experience: whether your page loads fast enough, whether users can interact with it promptly, and whether elements jump around annoyingly while loading. Google measures these in the Chrome User Experience Report using real visitor data from Chrome users who've opted in. At Ottawa SEO, we see sites fail Core Web Vitals mostly due to oversized images killing LCP, unoptimized JavaScript blocking INP, and lazy-loaded content or web fonts causing CLS. The thresholds are based on the 75th percentile of page loads, meaning 75% of visits to your URL must hit the good threshold. It's worth noting that while Google calls these "Core" Web Vitals, there are other Web Vitals metrics like Time to First Byte (TTFB) and First Contentful Paint (FCP) that matter for diagnosis but aren't direct ranking factors. The core three are what count for search rankings and the Page Experience signal. Most Canadian sites we audit pass CLS easily but struggle with LCP on mobile, especially on shared hosting or when using unoptimized WordPress themes with render-blocking resources.