What are Core Web Vitals, and why do they matter?
What the interviewer wants to hear
- LCP measures loading, good at 2.5 seconds or less
- INP measures responsiveness, good at 200 ms or less; replaced FID in 2024
- CLS measures visual stability, good at 0.1 or less
- Measured on real users at the 75th percentile (field data)
- Part of page experience; a ranking signal but not the main one
- Improve user experience and conversions
Model answer
Core Web Vitals are three metrics Google uses to measure real user experience. Largest Contentful Paint measures loading, meaning how fast the main content appears, and good is 2.5 seconds or less. Interaction to Next Paint measures responsiveness to clicks and taps across the visit, and good is 200 milliseconds or less; it replaced First Input Delay in March 2024. Cumulative Layout Shift measures visual stability, and good is 0.1 or less. Google judges them using field data from real Chrome users, the CrUX report, at the 75th percentile. They are part of page experience, which is a ranking signal, but relevance and helpful content matter more. The bigger benefit is business: faster, stable pages keep visitors and convert better. I check them in Search Console and PageSpeed Insights, and use lab tools to debug.
Can you answer it under time pressure?
Take a timed easy round and get scored on every answer.
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