Core Web Vitals · performance · 4 min read

The Core Web Vitals failures nobody talks about

INP is the new failure mode. Most sites haven't noticed.

When Google swapped FID for INP in March 2024, the share of sites passing Core Web Vitals dropped by ~40 percentage points overnight. Most teams either didn't notice or assumed it was a Lighthouse bug.

INP catches what FID missed: long handler chains on scroll, click, and key events. Modern React + state-heavy UIs fail INP all the time. The fix is rarely 'optimise CSS' — it's almost always 'split or defer JS work'.

If you haven't run a recent CrUX pull for your top URLs, you're probably failing INP without knowing it.

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