Interaction to Next Paint (INP) is a Core Web Vital metric that assesses a page's overall responsiveness to user interactions. It measures the time between a user interaction (like a click or key press) and the next visual update on the page. A poor INP score indicates that the page is slow to respond to user input, leading to a frustrating user experience. To provide a good experience, pages should strive for an INP of ≤ 200 ms (Long Animation Frames API | Web Platform | Chrome for Developers). This report summarizes the most common causes of poor INP scores and outlines strategies for optimization.
The primary causes of poor INP scores are related to JavaScript execution, rendering bottlenecks (Long Animation Frames), and the impact of third-party scripts. Optimizing JavaScript, addressing Long Animation Frames (LoAFs), and carefully managing third-party scripts are key to improving INP.
JavaScript-related issues are a significant cause of poor INP. Minimizing CPU processing by optimizing website code and reviewing third-party scripts can reduce INP. Techniques like breaking up long tasks and using native HTML and CSS features instead of JavaScript can improve performance.
- Minimizing CPU Processing: The best way to reduce INP is minimizing how much CPU processing that happens on your page.
- Asynchronous Code: Running code asynchronously ensures the UI remains responsive even when background tasks are running. You can also run more of your code asynchronously so that the user gets an immediate UI update even if some work is still ongoing.
Rendering bottlenecks, specifically Long Animation Frames (LoAFs), contribute to poor INP scores. LoAFs are rendering updates delayed beyond 50ms and can cause visual jank and delays in interactions. Addressing LoAFs is crucial for improving INP.
- Definition: A long animation frame — or LoAF — is a rendering update that is delayed beyond 50ms source.
- Impact: LoAFs contribute directly to poor Interaction to Next Paint (INP) scores, one of the critical metrics in Google’s Core Web Vitals source.
Third-party scripts can negatively impact INP. Identifying and optimizing or removing slow third-party scripts embedded on a website can improve responsiveness.
- Identification: DebugBear real user monitoring uses the Long Animation Frames API to show you which scripts have the biggest contribution to your Interaction to Next Paint score source.
Several techniques can be employed to optimize INP, including:
- Profiling Website Code: Profiling website code and reviewing third-party scripts are crucial for identifying and addressing INP bottlenecks.
- Yielding to the Main Thread: Techniques like yielding to the main thread using
setTimeoutand reducing JavaScript code by using native HTML and CSS features can improve INP.
Based on the analysis of search results, the following actionable insights and observations can be made:
- JavaScript Optimization is Key: Focus on minimizing CPU processing, using async operations, breaking up long tasks, and deferring non-critical scripts.
- Address Long Animation Frames (LoAFs): The LoAF API helps identify and address slow frame renders caused by unoptimized canvas drawing, heavy DOM updates, or garbage collection.
- Manage Third-Party Scripts: Identify and optimize or remove slow third-party scripts to improve responsiveness.
- Use Native Features: Reduce JavaScript code by using native HTML and CSS features to minimize the amount of work the browser needs to do.
- Profile Website Code: Regularly profile website code and review third-party scripts to identify and address INP bottlenecks.
By implementing these strategies, developers can significantly improve their INP scores and provide a better user experience.