Interaction to Next Paint.

Interaction to Next Paint (INP) is a Core Web Vital introduced as a replacement for First Input Delay (FID) in March 2024. It measures the latency of all user interactions—clicks, taps, keyboard inputs—throughout the entire page lifecycle, not just the first interaction. The score represents the worst interaction latency at the 98th percentile, giving a reliable picture of overall interactivity.

INP Thresholds

Google's thresholds: Good = under 200 milliseconds; Needs Improvement = 200–500 ms; Poor = over 500 ms. INP failing is most common on JavaScript-heavy pages where large scripts block the main thread, preventing the browser from processing user interactions quickly.

Improving INP

INP improvement strategies: break up long JavaScript tasks (over 50ms) into smaller chunks using `scheduler.yield()` or `setTimeout`; defer non-critical JavaScript until after user interaction; reduce the amount of JavaScript parsed and executed on page load; optimise event handlers to complete quickly; and use web workers for computationally intensive tasks to keep the main thread free for user interactions.