What are Core Web Vitals?
Core Web Vitals are Google's metrics for measuring real-user page experience: LCP (Largest Contentful Paint — loading), CLS (Cumulative Layout Shift — visual stability), and INP (Interaction to Next Paint — responsiveness).
Why they matter for solo SaaS
Two reasons: (1) Google uses CWV as a ranking signal — poor scores hurt your SEO. (2) Poor CWV correlates with worse conversion rates. Slow or jumpy pages cost you signups.
LCP: The most important metric
LCP measures how long until the largest content element (usually a hero image or heading) is visible. Target: under 2.5s. Common causes of poor LCP for SaaS: large unoptimized hero images, render-blocking JavaScript, slow server response.
CLS: The annoying one
CLS measures layout shifts — things moving around after they've rendered. Target: under 0.1. Common causes: images without width/height attributes, dynamically injected content, web fonts loading.
INP: The new one
INP (replaced FID in 2024) measures how quickly your page responds to interactions. Target: under 200ms. Common causes of poor INP: long JavaScript tasks blocking the main thread, heavy event handlers.
Measuring real user CWV
PageSpeed Insights gives you lab data. ProdFix gives you real user data — actual CWV values from your actual users on their actual devices and networks. These often differ significantly. Fix based on real user data.
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