INP

INP (Interaction to Next Paint) measures responsiveness across every click, tap and key press in a session and reports a value close to the worst case. It replaced FID as an official Core Web Vital in March 2024.

Where FID only looked at the very first interaction, INP captures the whole session — which makes it noticeably harder to pass. Thresholds: 200 ms or below is good, above 500 ms needs improvement.

Heavy JavaScript work is the dominant cause of poor INP scores. The standard playbook is to break up long tasks, keep event handlers thin, and move expensive work into requestIdleCallback or web workers.