Optimizing INP: Mastering Core Web Vitals in 2025 for a Fast, Responsive Site

Since March 2024, Google has officially replaced FID (First Input Delay) with a new key metric: INP, for Interaction to Next Paint. This change, seemingly minor, is nonetheless upending the benchmarks of front-end developers and SEO teams. Unlike FID, which only measured the user's very first interaction, INP captures the latency of all the interactions performed on a page. The result: performance metrics become much more demanding, and front-end optimization can no longer be limited to a fast load time. You now have to guarantee consistent responsiveness throughout the user session.

INP: a metric more representative of the real user experience

INP measures the time elapsed between a user interaction (click, key press, tap) and the moment the interface actually starts responding visually to that interaction. So it is not just a test of the first impression: it is an overall indicator of the perceived smoothness across the entire page.

Google recommends keeping an INP value below 200 milliseconds at the 75th percentile. Between 200 and 500 ms, performance is considered "needs improvement." Above 500 ms, the page is deemed poorly responsive, which can have a negative SEO impact.

👉 Official Google documentation: Introduction to INP

Why INP is becoming a central SEO issue

The inclusion of INP in the Core Web Vitals confirms Google's intention to favor sites that offer smooth navigation and a good user experience. Where FID settled for a single signal on the first interaction, INP enables a continuous assessment of responsiveness.

This is a major change: a site that seems fast when loading can still suffer critical slowdowns during actual use. For Google, this kind of latency harms the user experience and deserves to be penalized in the rankings.

For an overview of these changes and how they relate to SEO, you can read our article dedicated to the Google SEO 2025 update

How to measure and diagnose INP

INP is measured from field data, collected on users' real browsers (notably via Chrome). This provides a representative view of the performance actually perceived, beyond lab tests.

Several Google tools let you view or use this data:

• PageSpeed Insights
• Google Search Console

In addition, developers can analyze interaction delays locally using the performance tools in Chrome DevTools.

Optimizing INP: what it means on the development side

Improving INP requires a paradigm shift: it is no longer enough to optimize the initial load; you also need to lighten everything that happens during the interaction. JavaScript must be kept under control, long tasks must be broken up, and the interface must stay responsive even after several minutes of browsing.

This involves:

• deferring the execution of non-essential scripts,
• splitting up heavy or redundant components,
• simplifying the DOM to limit the cost of reflows,
• prioritizing the visual rendering of interactive areas,
• controlling animations or visual effects triggered on interaction.

Integrating INP into your development processes

The best way to keep INP under control is to build it into your tools and workflows. In production, regular monitoring of the Core Web Vitals lets you track how they evolve over time, as deployments and new features roll out. Upstream, you can include Lighthouse tests in your CI processes to catch regressions during development.

It also makes sense to align your product metrics and your SEO goals: if your conversion funnel suffers from latency on mobile, the impact will be felt on user experience, on search rankings and ultimately on your conversion rates.

Conclusion

The arrival of INP as the main Core Web Vital for responsiveness is a logical but demanding step forward. It requires developers to pay continuous attention to JavaScript performance and front-end architecture. A site that loads fast is no longer enough: it must also stay smooth and responsive throughout the browsing session. By anticipating these expectations and structuring your projects around continuous performance, you give yourself every chance to strengthen your SEO, your product quality and your conversion.

Concretely improve your site's performance

If you want to improve your Core Web Vitals (including INP) on a showcase or e-commerce site:

• Discover our Web & e-commerce offering focused on performance, SEO and conversion.
• If your challenge goes beyond the website (internal tool, business portal...), our custom development team can support you on a broader foundation.
• You can also contact us to audit the state of your site and define a prioritized action plan.