Interaction to Next Paint (INP) is a crucial web performance metric that directly impacts user experience. Let's dive into what INP is, why it matters, and how to enhance it for better responsiveness.

What Is Interaction to Next Paint (INP)?

Interaction to Next Paint (INP) measures how quickly a web page responds to user interactions. Unlike the First Input Delay (FID) metric, which only considers the first interaction with a page, INP captures all interactions throughout the user session. It's a full-page lifecycle metric, similar to Cumulative Layout Shift (CLS).

Why INP Matters?

Over the past year, the availability of INP as an experimental metric has revealed that many pages and sites underperform in terms of responsiveness. While the 75th percentile of site users showed few responsiveness issues according to FID, INP highlights moderate to poor user experience (UX), especially for smartphone visitors. In fact, if INP were a Core Web Vitals (CWV) metric today, only 20% of the top 1,000 mobile websites would have good CWV with INP, a decrease of 32 percentage points compared to FID (52%).

Prompt Visual Feedback: Key to INP

When a page responds quickly to user interactions, we call it good responsiveness. Users perceive responsiveness through visual feedback. This feedback appears in the next frame the browser renders after the interaction occurs. Examples include a mobile navigation menu opening, an item added to a shopping cart, or validation notifications for input fields in a registration form.

For INP, providing prompt visual feedback is vital. The time between a user interaction and when the next frame is painted should be as short as possible. If a backend server or third-party resource is invoked after an interaction, visual hints become even more critical due to additional network latency and backend processing times.

How to Solve INP Issues?

Here are some actionable steps to improve INP:

1. Analyze Browser Main Thread Activity: Use tools like Lighthouse's timespan mode to identify INP issues and understand interaction delays involved.

2. Optimize Input Delay: Minimize JavaScript Execution Time: Review your JavaScript code and identify areas for optimization. Minify and optimize scripts to reduce execution time.

Prioritize Critical Tasks: Ensure that essential tasks execute promptly. Consider lazy loading non-essential scripts to prevent them from blocking critical interactions.

Evaluate Third-Party Scripts: Assess third-party scripts and remove any unnecessary ones. Loading them asynchronously can prevent delays.

3. Optimize Event Callbacks: Efficiently handle event callbacks to minimize processing delay. Well-optimized event handling ensures smoother interactions.

4. Paginate Comments: If your website receives many legitimate comments, consider paginating them. This prevents performance bottlenecks during page rendering.

5. Reduce or Remove Duplicate Widgets: Duplicate widgets contribute to longer presentation delays. Streamline your design by eliminating unnecessary duplicates.

6. Simplify Menus: Complex navigation menus can hinder responsiveness. Streamline your menu structure to improve user interaction speed.

7. Disable Sticky Menus: While sticky menus provide convenience, they can impact responsiveness. Evaluate whether sticky behavior is essential for your site and disable it if possible.

8. Consider Removing Scroll-to-Top Buttons: These buttons, while useful for navigation, introduce additional interactions. Assess their necessity and remove them if they cause delays.

9. Remove Underperforming Opt-In Forms: Opt-in forms that load slowly can negatively affect INP. Evaluate their performance and consider alternatives if needed.

10. Provide Prompt Visual Feedback: When a page responds quickly to user interactions, it’s considered good responsiveness. Users perceive responsiveness through visual feedback. Ensure that the time between a user interaction and the next frame being painted is as short as possible.

Remember that addressing INP directly leads to a better user experience. By implementing these tips, you’ll enhance your site’s responsiveness and overall performance1. Keep monitoring your metrics and iterate on improvements to ensure a seamless user experience!