INP Replaced FID. Here Is What That Actually Means for Your Site.
· 5 min read
Interaction to Next Paint (INP) replaced First Input Delay (FID) as a Core Web Vitals metric in March 2024. As of 2026, it is still the metric where I see the most persistent gaps in client audits — not because teams are unaware of it, but because fixing INP requires a different kind of debugging than what most front-end teams are used to.
This post covers what INP actually measures, why it is harder to fix than FID, and what a realistic optimization process looks like.