Understanding INP (Interaction to Next Paint) in Web Performance Metrics: The Role of Core Web Vitals
Introduction to Core Web Vitals and INP
In recent years, Google has placed increased emphasis on web performance, particularly with regard to how quickly and smoothly a website loads and responds to user interactions. Core Web Vitals (CWV) are a set of user-centric metrics developed by Google to measure the overall experience of users interacting with a website. These metrics are critical for understanding how a website performs in real-world scenarios, reflecting both loading times and user interaction experience.
One of the newer and significant additions to Core Web Vitals is INP (Interaction to Next Paint). INP measures how quickly the browser responds to user interactions, offering an insight into how well a website delivers a seamless, responsive experience to its users.
What is INP (Interaction to Next Paint)?
INP is a metric introduced by Google as a part of its initiative to improve real user experiences on the web. It focuses on user interactions and the time it takes for the next paint after the user interacts with a website, such as clicking a button or typing into a form field. Specifically, INP measures the time between the user’s interaction (e.g., a click or keypress) and the visual response (the next paint) on the screen.
This metric is a valuable supplement to the widely known First Input Delay (FID), which measures the time it takes for the browser to respond to the first user input. However, INP takes a broader view by measuring all interactions throughout a session rather than just the first input, thus providing a more comprehensive picture of user experience.
How INP Works
INP tracks the interaction events on a page, such as:
- Clicks
- Key presses
- Touch gestures (on mobile)
- Mouse movements
When an interaction occurs, INP measures how long it takes for the page to visually respond with the “next paint,” which is the next frame that visually changes the state of the webpage after the interaction. This includes scenarios like clicking a button that causes a modal window to appear, pressing a key in a text input that updates the content, or tapping on a mobile screen to trigger a page transition.
The performance of INP is based on the most significant interaction that occurs during the user’s session. This means that for every user session, the interaction with the longest delay will determine the INP score for that session.
Why is INP Important?
INP is important because it directly measures how responsive a webpage feels to users. While metrics like Largest Contentful Paint (LCP) and First Input Delay (FID) measure aspects of page load and first interaction performance, INP focuses on the ongoing user experience. The metric is essential in situations where users interact multiple times with a page, and responsiveness could significantly impact their experience.
If a webpage has long delays in response to interactions, users may perceive the website as sluggish or unresponsive, which can lead to frustration and potential abandonment of the page. On the other hand, fast and responsive websites foster a better experience, improving engagement and user satisfaction.
INP and User Experience
A poor INP score can have a significant negative effect on user experience. Websites that fail to respond quickly to interactions can cause users to feel disconnected or frustrated. Consider a scenario where a user clicks on a button, and the response time is too slow — the user may abandon the interaction altogether or leave the website.
Conversely, a fast INP score means the website responds immediately to user actions, creating an intuitive and smooth interaction. This leads to improved user engagement, higher conversion rates, and ultimately better overall site performance.
INP and its Role in Core Web Vitals
INP complements other Core Web Vitals metrics, such as:
- Largest Contentful Paint (LCP): Measures the time it takes for the largest element in the viewport to load, providing insight into how quickly content is visually presented to users.
- First Input Delay (FID): Measures the time it takes for the browser to respond to the first interaction from the user, which is a key factor in assessing the interactivity of a webpage.
- Cumulative Layout Shift (CLS): Measures the visual stability of the page as users interact with it, ensuring that elements don’t unexpectedly shift or move during interactions.
INP extends these metrics by evaluating ongoing interactions throughout a session. This holistic view of performance is particularly valuable because users interact with websites multiple times during their visit. Monitoring these interactions can help developers understand the overall smoothness and responsiveness of their web application.
Best Practices for Improving INP
To ensure a fast and responsive interaction experience for users, web developers should focus on improving the performance of INP. Some best practices for achieving this include:
- Optimize JavaScript and CSS: Complex or bloated scripts and stylesheets can delay interactions, so minimizing and optimizing JavaScript execution is essential. Techniques such as code splitting, lazy loading, and defer loading non-essential JavaScript can help reduce delays.
- Use Web Workers: Offload time-consuming tasks to background threads (via Web Workers) so they don’t block the main thread, allowing the page to remain responsive during heavy tasks.
- Minimize Repaints and Reflows: Unnecessary reflows (layout recalculations) and repaints (redrawing parts of the page) can cause significant delays after user interactions. Minimizing these can help improve INP.
- Reduce Third-Party Scripts: Third-party scripts (like ads, analytics, or widgets) can introduce performance bottlenecks. It’s essential to assess their impact and delay their execution until the page is fully interactive.
- Prioritize Critical Interactions: Focus on optimizing the most frequent and critical user interactions, such as button clicks or form submissions, to ensure these actions are handled swiftly.
- Reduce Main Thread Work: The main thread (the thread that handles rendering, JavaScript, and user interactions) can be a bottleneck if overloaded. Offloading work to Web Workers and splitting JavaScript into smaller chunks can help reduce the main thread’s workload.
INP Benchmarks and Goals
Google recommends that good INP scores should be below 200 milliseconds, which means that the time between a user’s interaction and the next visual response should ideally be under 200ms for an optimal experience. Scores above 200ms may indicate performance issues that need to be addressed to enhance the user experience.
- Good INP: <200ms
- Needs Improvement: 200ms – 500ms
- Poor INP: >500ms
By aiming to achieve these benchmarks, developers can ensure that their websites provide the best possible experience for users.
Conclusion
INP is an essential web performance metric that measures how responsive a website is to user interactions. Unlike other Core Web Vitals, which focus primarily on loading and initial interaction, INP provides a more complete view of the ongoing user experience. A strong INP score can significantly enhance user satisfaction, leading to better engagement and retention. By following best practices such as optimizing JavaScript, minimizing reflows, and reducing third-party scripts, developers can improve INP and deliver a more responsive and seamless experience for users.
As web performance continues to play a critical role in SEO and user experience, understanding and optimizing INP is more important than ever.