Introduction

Web performance is no longer a technical detail but a game changer in how users experience the internet. The newest kid on the block of core web vitals is Interaction to Next Paint (INP). This new metric bridges the gap that measures how responsive a web page is, looking towards becoming the eventual measure of interaction latency, where it could actually replace First Input Delay (FID).

We will delve deep into what INP is about, why you should care about it, how you can measure INP, and some actionable tips you can apply right away to drive improvement.

What is INP?

So, what is INP? In simple words, it measures the time elapsed from when a user interacts with a website, such as clicking a button or typing in a form, until the next visual update pops up on the screen. The idea here is to capture the delay that users actually feel when they engage with a site.

Unlike FID, which only looks at how long it takes for the browser to respond to a user's input, INP takes a broader view. It examines the entire process, from the initial delay to the visual response, giving a more complete picture of a site's responsiveness.

Why Does INP Matter?

1. User Experience

Let's face it: when we interact with a website, we want things to happen fast. If there's a noticeable lag, it's frustrating. High latency can lead to unhappy users, less engagement and even abandonment of the site altogether.

2. Holistic Responsiveness

FID only shows a part of the puzzle: how busy the main thread of the browser is. But that is just the beginning. INP fills in the gaps by measuring the total delay a user perceives, making it more solid than FID as a measure of responsiveness.

3. Future-Focused Metric

Google is going to integrate INP into its ranking algorithms, so getting a grip on INP now can put you ahead in search rankings later.

How is INP Measured?

To measure INP for a single page view, you do the following:

1. Track all user interactions—clicks, taps, and key presses—during a session.
2. Note the time it takes for each interaction to result in a visual update on the screen.
3. The INP score for that page is based on the longest interaction delay you measured.

This way, you're viewing the worst-case scenario for responsiveness, which is vital for user perception.

INP Scoring Guidelines:

• Good: INP ≤ 200ms
• Needs Improvement: 200ms < INP ≤ 500ms
• Poor: INP > 500ms

Diagnosing and Improving INP

Now that we know what INP is, let's discuss how to make it better! Here are some strategies for optimizing the different phases of handling user interactions:

1. Reduce Input Delay

• Audit Your Main Thread: Use tools like Chrome DevTools to spot tasks blocking the main thread and break them into smaller, manageable chunks.
• Optimize JavaScript: Clean up your code—minimize, compress, and eliminate any unused JavaScript. If you're using tools like React, take advantage of concurrent rendering to help distribute tasks more efficiently.

2. Improve Event Handling

• Debounce and Throttle: For high-frequency events like scrolling or resizing, use techniques to limit how often they trigger additional processes.
• Use Passive Event Listeners: Improve performance on touch and scroll events by applying passive listeners.

3. Optimize Painting

• Reduce Layout Shifts: Avoid changing the DOM as much as possible, and always use CSS transitions instead of JavaScript.
• Focus on Priority Paints: Use Lighthouse to determine what parts of your site need to be painted in priority and focus on those pathways.

4. Use Browser Optimizations

• Preload Essential Resources: Prepare your fonts, images, and scripts ahead of time so that they are there when users demand them.
• Use Web Workers: Push heavy computations to web workers to prevent blocking the main thread.

Tools for Measuring INP

To keep tabs on your INP, consider using these handy tools:

• Lighthouse: This tool audits your site’s responsiveness and offers practical advice on how to improve.
• Chrome DevTools Performance Panel: Analyzes interaction timelines and latencies.
• PageSpeed Insights: Provides you with real time data from the field to measure INP and provides recommendations for improvement.

Conclusion

INP or Interaction to Next Paint, is a transformational metric that puts UX first in the world of web performance. It represents how well your site responds to realistic interactions, making it an important factor in user satisfaction and search engine optimization. By learning about INP and putting strategies in place to enhance it, you’re not just keeping up with evolving performance standards—you’re also ensuring your users enjoy a seamless, delightful experience every time they visit your site. If you like this blog and want to learn more about Frontend Development and Software Engineering you can follow me on Dev.to.