What is Interaction to Next Paint (INP) and How to Master It?

Interaction to Next Paint (INP) changed everything in March 2024. Google made it an official Core Web Vital.

This means your website’s search ranking now depends on how fast it responds to clicks, taps, and keyboard presses.

What is Interaction to Next Paint?

INP measures how quickly your website responds when users interact with it. Click a button. Tap the screen. Press a key. INP tracks the time from that action until you see the result on screen.

However, INP doesn’t just measure one interaction. It watches every single interaction during a user’s entire visit. Then it takes the slowest one as your final score.

Key Point: INP replaced First Input Delay (FID) because it gives a complete picture of your site’s responsiveness. FID only looked at the first click. INP monitors everything.

Why INP Matters for Your Website

Google uses INP as a ranking factor. Sites with good INP scores rank higher in search results. But there’s more to it than SEO. Think about your browsing habits.

You click something and expect an immediate response. When nothing happens, you get frustrated. You might even leave the site entirely.

A slow INP score indicates a sluggish, frustrating website. Users bounce faster. They spend less time on your pages. These negative signals tell Google your site provides a poor experience.

Understanding Your INP Score

Your goal is simple: stay under 200ms. However, achieving this requires understanding how INP works behind the scenes.

Google sets clear thresholds for INP performance:

The Three Phases of Every Interaction

Every interaction has three phases:

1. Input Delay: The time from your click until the browser starts processing it
2. Processing Time: How long the browser takes to run the code and prepare the response
3. Presentation Delay: The time needed to update what you see on screen

Problems in any phase will hurt your INP score. For example, if JavaScript is running when you click, the browser can’t respond immediately. This creates input delay.

How to Measure INP

You need real-world data to understand your INP performance. Lab tests help, but they don’t show what actual users experience.

Real User Monitoring (RUM)

RUM tools collect data from real visitors. They show which pages have problems and what types of interactions are slow. This information is invaluable for fixing specific issues.

Chrome User Experience Report (CrUX)

CrUX provides free INP data through tools like PageSpeed Insights. It’s a good starting point. However, it lacks detailed context about why interactions are slow.

Chrome DevTools for Debugging

The Performance panel in Chrome DevTools shows exactly what happens during slow interactions. Record a session while reproducing the problem. You’ll see a visual timeline showing where time is spent.

Look for “Long Tasks” – any single task taking over 50ms. These block the main thread and prevent quick responses to user input.

Proven Strategies to Improve INP

Break Up Long Tasks

Long tasks are INP’s biggest enemy. They block the main thread and delay responses to user input.

Break large tasks into smaller chunks. Use functions like setTimeout or scheduler.yield to pause work and let the browser handle user interactions.

For heavy calculations, consider Web Workers. They move intensive work off the main thread entirely.

Optimize JavaScript Performance

Heavy JavaScript hurts INP scores. Code splitting helps by loading only necessary scripts. Server-side rendering can also reduce client-side JavaScript work.

Manage DOM Complexity

Large, complex page structures slow down visual updates. When users interact with your page, the browser must recalculate styles and repaint elements.

Simplify your HTML structure. Use fewer nested elements. Choose efficient CSS selectors to avoid unnecessary work.

Provide Immediate Feedback

Show users something immediately after they interact, even if background processing continues. A simple loading spinner can dramatically improve your INP score.

This works because INP measures time to the next paint, not completion of the entire task.

Common Mistakes to Avoid

• Running heavy tasks on the main thread: Always move intensive work elsewhere
• Multiple unnecessary event handlers: One interaction shouldn’t trigger multiple unrelated processes
• Blocking primary actions with secondary tasks: Don’t make users wait for analytics while opening a menu
• Overusing timers: Frequent setInterval calls can keep the main thread busy

Expert Best Practices

• Profile with DevTools: Use the Performance panel to analyze each interaction phase
• Defer non-critical work: Move secondary tasks out of main interaction handlers
• Do less work: Write efficient code and minimize computational load
• Use RUM data strategically: Focus optimization efforts on the worst-performing areas

Key Takeaways

INP is now a critical Core Web Vital. It measures your site’s responsiveness throughout the entire user visit. Not just the first click.

The main culprit behind poor INP scores is a busy main thread blocked by long tasks. Fix this by breaking up heavy work and using Web Workers for intensive calculations.

Measure INP with real user data to identify problems. Debug with Chrome DevTools to find solutions. This combination provides both insight and actionable fixes.

Remember: a good INP score improves both SEO rankings and user experience. However, it’s just one part of a comprehensive performance strategy. Focus on creating genuinely fast, responsive websites that users love to use.