Glossary
INP
In short: Interaction to Next Paint (INP) is the Core Web Vital that measures how long a page takes to visually respond after a user taps, clicks or presses a key.
Interaction to Next Paint replaced First Input Delay as a Core Web Vital in March 2024. Where FID measured only the first interaction and only the delay before the browser started handling it, INP looks at every interaction during a visit and measures the full time until the next frame is painted. The reported value is close to the worst interaction a typical user experiences.
The thresholds are 200 milliseconds or under for "good", 200 to 500 for "needs improvement", and over 500 for "poor", measured at the 75th percentile of real visits.
INP problems usually come from JavaScript doing too much work on the main thread: heavy third-party scripts (chat widgets, tag managers, consent tools), large frameworks hydrating the whole page, and event handlers that run expensive code synchronously. Typical fixes are deferring non-essential scripts, breaking long tasks into smaller chunks, reducing DOM size and giving immediate visual feedback before heavy work runs.
For a service business the symptom is simple: a booking button or quote form that feels sluggish on a mid-range phone. Seoptist reports INP for mobile and desktop from PageSpeed Insights data, tracks the trend, and lists the scripts and long tasks responsible so they can be assigned and fixed from the checklist.