Core Web Vitals are the three Google-measured metrics that summarize page experience quality. Google uses them as a ranking factor (modest direct effect, larger indirect effect through user behaviour signals), and they correlate strongly with conversion outcomes regardless of search ranking. **Largest Contentful Paint (LCP).** Time from navigation start to when the largest visible content element renders. Target: under 2.5 seconds on mobile. Common causes of slow LCP: large unoptimized hero images, server response time, render-blocking JavaScript, slow CDN delivery, fonts loading before LCP element. Fixes for LCP: - Compress and serve hero images in WebP or AVIF format at appropriate sizes (don't serve a 4000px image to a 400px container). - Preload the LCP image with `<link rel="preload" as="image">`. - Move render-blocking scripts to defer or async. - Inline critical CSS for above-the-fold content. - Use a CDN with edge nodes near your users (most major CDNs have Canadian edge presence). - Improve server response time (Time to First Byte under 600ms ideally). **Interaction to Next Paint (INP).** Time from user interaction (click, tap, key press) to next paint reflecting the response. Target: under 200ms. Replaced First Input Delay in March 2024 as the responsiveness metric. Common causes of slow INP: heavy JavaScript blocking the main thread, unoptimized event handlers, large component re-renders, third-party scripts. Fixes for INP: - Audit and minimize third-party scripts (analytics, chat widgets, ad scripts often dominate). - Code-split bundles so each page only loads what it needs. - Move heavy work off the main thread with Web Workers where applicable. - Use `requestIdleCallback` for non-critical initialization. - Avoid synchronous layout thrashing in event handlers. - Test on mid-range mobile devices (the Moto G Power tier), not flagship phones — most Canadian users are on mid-range hardware. **Cumulative Layout Shift (CLS).** Sum of unexpected layout shifts during page lifetime, weighted by impact area and shift distance. Target: under 0.1. Common causes of CLS: images and iframes without explicit dimensions, web fonts swapping after load (FOUT/FOIT), dynamically injected content (banners, ads, cookie consent dialogs), third-party widgets without reserved space. Fixes for CLS: - Set explicit width and height attributes on all `<img>` and `<iframe>` elements. - Reserve space for fonts via `font-display: optional` or `size-adjust` techniques. - Reserve space for dynamically injected content (cookie banners, ads) using container divs with min-height. - Test for layout shifts during the entire page lifecycle, not just initial load. **Measurement.** Google Search Console's Core Web Vitals report shows real-user data from Chrome User Experience Report (CrUX). PageSpeed Insights provides both lab data (synthetic test) and field data (real users). Lab and field data often diverge — field data is what Google uses for ranking signals. **Realistic expectations.** Most Canadian SMB sites fail at least one Core Web Vital initially. Focused remediation typically achieves 'Good' status across all three within 4–8 weeks of work. Sustaining 'Good' status requires ongoing discipline as new content and features are added — performance regressions accumulate quickly without monitoring.