We spent years teaching clients to watch Largest Contentful Paint. Hero images, preload tags, CDN moves: the story was easy to tell in a slide deck. When Interaction to Next Paint became a Core Web Vital in March 2024, most of our accounts already had a green LCP on the homepage. What we had not built was a habit of measuring the clicks that happen after that paint.
Interaction to Next Paint (INP) is a field Core Web Vital about responsiveness across a visit, not a single moment at load. That sounds obvious on paper. In production it meant we were auditing the wrong URLs, trusting the wrong proxies, and celebrating fixes that never touched the menu, the cart step, or the filter drawer where users actually waited.
What we measured before INP (and the gaps we left open)
Our default audit pack looked like a loading problem: homepage, maybe a top landing page, PageSpeed Insights, a Lighthouse export, a note on LCP and Cumulative Layout Shift. First Input Delay had rarely failed on those runs anyway, so "interactivity" felt solved once the main thread cleared the first second.
We skipped, or measured only once:
