What is INP?Interaction to Next Paint (INP) is one of Google three Core Web Vitals, measuring the responsiveness of a web page to user interactions. It captures the latency from the moment a user clicks, taps, or presses a key to the moment the browser renders the next visual update in response. INP replaced
What is INP?
Interaction to Next Paint (INP) is one of Google three Core Web Vitals, measuring the responsiveness of a web page to user interactions. It captures the latency from the moment a user clicks, taps, or presses a key to the moment the browser renders the next visual update in response. INP replaced First Input Delay (FID) as an official Core Web Vital in March 2024. Unlike FID, which only measured the delay before the browser could process the first interaction, INP measures the full interaction response time throughout the page lifecycle. Google thresholds: 200ms or less is Good, 200-500ms is Needs Improvement, above 500ms is Poor.
Why INP Matters for SaaS Applications
SaaS websites and web applications are particularly vulnerable to poor INP because they often use JavaScript-heavy frameworks like React, Vue, or Angular and load large amounts of client-side logic. Common INP issues include: long JavaScript tasks blocking the main thread, heavy event handlers on buttons and form fields, large React component trees that re-render slowly, and analytics and tracking scripts that compete for CPU during interactions. For SaaS apps with interactive dashboards, calculators, or live demos embedded in marketing pages, INP is a critical metric.
How to Improve INP
Key INP improvements include: breaking up long JavaScript tasks into smaller chunks using async/await or setTimeout, deferring non-critical scripts, moving heavy computations off the main thread using Web Workers, implementing code splitting to reduce initial JavaScript bundle size, optimizing React rendering with useMemo and useCallback, and auditing third-party scripts for interaction latency.
Frequently Asked Questions
How is INP measured in the real world versus the lab?
Lab tools like Lighthouse measure INP by simulating typical user interactions. Real-world field INP is measured from actual Chrome users and reported in Google Search Console and CrUX data. Field INP is often worse than lab INP because real users may have slower devices or run multiple browser tabs.
What is the difference between INP and FID?
FID only measured the delay before the browser started processing the very first user interaction on a page. INP measures the full response latency for all interactions throughout the session and reports the worst-performing interaction. INP is a more rigorous and representative metric, which is why Google replaced FID with it in 2024.