A site fails Core Web Vitals on mobile. How would you find and fix the problems?
What the interviewer wants to hear
- Use field data (CrUX, Search Console) to find failing metric and templates
- LCP: server response, hero image, render-blocking resources
- INP: long JavaScript tasks, third-party scripts
- CLS: reserve space for images, ads, fonts
- Work with developers and re-measure
Model answer
First I use field data from the Search Console Core Web Vitals report and PageSpeed Insights to see which metric fails and on which page templates, since fixing a template fixes thousands of pages. For LCP, I check server response time, make the hero image smaller and in modern formats like WebP or AVIF, preload it, and remove render-blocking CSS or JavaScript. For INP, I look at long tasks in Chrome DevTools, reduce or delay heavy third-party scripts like chat widgets and trackers, and ask developers to break up long tasks. For CLS, I make sure images and ads have fixed sizes and fonts load without big layout jumps. I write clear tickets with evidence, then track field data for 28 days to confirm improvement.
Can you answer it under time pressure?
Take a timed medium round and get scored on every answer.
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