Q1. What are Core Web Vitals and what thresholds define a good experience?
Core Web Vitals are user-centric metrics for loading, interactivity and visual stability. LCP, Largest Contentful Paint, measures when the largest visible element, usuall...
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Q2. How do you improve Largest Contentful Paint?
LCP is dominated by four factors: time to first byte, resource load time, render-blocking resources and client-side rendering delay. First ensure fast TTFB with caching, ...
Q3. What causes Cumulative Layout Shift and how do you fix it?
CLS measures how much visible content moves unexpectedly. The score for a shift is the impact fraction times the distance fraction, summed over the session, excluding shi...
Q4. What is INP and how do you reduce it?
Interaction to Next Paint measures the time from a user interaction such as a click, tap or key press until the browser paints the next frame, across the whole visit, rep...
Q5. What is the critical rendering path and how do you optimise it?
The critical rendering path is the sequence the browser follows to turn HTML, CSS and JavaScript into pixels: parse HTML into the DOM, parse CSS into the CSSOM, combine t...
Q6. How do lazy loading and code splitting improve performance?
Lazy loading defers work until it is needed. For images, loading="lazy" and decoding="async" defer off-screen loads, but never lazy-load the LCP image because it delays t...
Q7. How do HTTP caching and CDNs improve performance?
Caching avoids re-downloading assets and is one of the cheapest performance wins. Use content-hashed filenames with a long Cache-Control: public, max-age=31536000, immuta...
Q8. How do lab and field performance measurement differ?
Lab tools run in a controlled environment. Lighthouse gives a synthetic score with TTFB, FCP, LCP, TBT and CLS, which is useful in CI and for reproducible comparisons. Ch...