From FID to Google INP. Everything You Need to Know about Interaction to Next Paint (INP)


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In the depths of the evolution of web performance metrics, Google ushered in a new era with Interaction to Next Paint (INP), a metric intended to outperform First Input Delay (FID) in Core Web Vitals. This innovation promises to offer a more complete and precise view of the user experience when interacting with a web page.

The Essence of Interaction to Next Paint (INP)

INP is notable for its focus on the time it takes for the browser to “paint” the next frame after user interaction. While FID focuses on the first interaction, INP spans the entire page lifecycle, providing a more representative measure of user experience. Simply put, it measures the period between user input and when the browser makes a change visible on the page.

Comparison with FID: A View Beyond the First Interaction

While FID manages the time between the first input and the browser response, INP extends this measure to the time needed to make the next change visible. INP offers a comprehensive overview of the user experience throughout the entire visit, revealing interactive dynamics over time.

Defining a “Good” INP Value

The challenge of assigning labels such as “good” or “poor” to a responsiveness metric is answered in the 75th percentile of page loads:

  • INP ≤ 200 ms: Represents excellent responsiveness.
  • 200 ms < INP ≤ 500 ms: Signals the need for improvements in responsiveness.
  • INP > 500 ms: Indicates poor responsiveness.

Analysis of the Causes of Poor INP Performance

Prolonged JavaScript executions on the main thread emerge as the root cause of INP-related issues. WordPress plugins, third-party scripts, and using frameworks like Vue or React can contribute to a higher INP. Ineffective JavaScript code within the WordPress theme itself can further degrade performance.

Strategies for Measuring and Improving NPI

As a field metric, INP requires analysis of real user data via tools like Chrome User Experience Report. Lighthouses and performance analyzers can spot sustained JavaScript activity and optimize resource usage, helping improve INP.

Meeting the Challenge of INP Debugging

Debugging INP represents a greater challenge than FID, as it covers the entire cycle of user interaction with the site. Analysis using developer tools can reveal costly scripting tasks or massive rendering updates. The Chrome documentation provides a comprehensive guide on optimizing INP.

Conclusion: The Bright Future of Web Responsiveness

INP is not just a new metric; it is a tangible sign of the growing importance of providing responsive, interactive and user-centered websites. Its inclusion in Core Web Vitals will not only improve your search engine position but represents a commitment to delivering superior user experiences.

Get ready for the user experience revolution with INP: the future of web responsiveness is here, and INP optimization is the next step towards a new standard of excellence.

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