Teams spend weeks shaving kilobytes off JavaScript while a single unoptimised hero image quietly owns the score. Core Web Vitals reward a small number of specific fixes, and most sites have not done them yet.
Largest Contentful Paint
On nine out of ten pages the LCP element is an image or a heading above the fold. Serve that image in a modern format, size it correctly for the viewport, and preload it. Everything else is refinement.
Interaction to Next Paint
- Break long tasks apart so the main thread can answer a tap.
- Defer analytics and chat widgets until after first interaction.
- Watch third-party scripts. They are usually the ones blocking.
Cumulative Layout Shift
Reserve space. Width and height attributes on images, fixed heights on ad slots, and font loading that does not swap into a wildly different metric. CLS is the cheapest of the three to fix and the most commonly ignored.
Measure with field data, not a lab run on your own machine. Your laptop on fibre is not your customer on a three year old phone.
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