Core Web Vitals and SEO: A Developer’s Primer

Google’s experience signals reward pages that feel fast, stable, and responsive. The three headline metrics are LCP, INP, and CLS.

Largest Contentful Paint (LCP)

Measures when the main content paint completes. Heavy hero images, slow fonts, and server response time are usual suspects.

Interaction to Next Paint (INP)

Replaces the older FID mindset with a broader look at interactivity delay after user input.

Cumulative Layout Shift (CLS)

Penalizes unexpected layout jumps — often ads, late-loading fonts, or images without dimensions.

How to work with them

• Measure in field data (RUM) when possible, not only lab Lighthouse runs.
• Guard performance in CI: budget key routes after each deploy.

Great vitals support SEO, but the real win is happier users who stay and convert.