What Is INP? A Complete Explanation of Interaction to Next Paint
Interaction to Next Paint (INP) is a critical web performance metric that measures how responsive websites are to user interactions. As a key replacement for First Input Delay (FID) starting in March 2024, INP offers a comprehensive analysis of site responsiveness throughout a user’s session.
- INP measures the delay between user interactions and visual feedback, with optimal performance under 200ms.
- Unlike FID, INP evaluates every interaction, offering a complete view of user experience.
- It comprises three components: input delay, processing time, and presentation delay.
- Performance issues often stem from heavy JavaScript execution, inefficient event handlers, and complex DOM updates.
- Optimizing INP involves breaking up long tasks, refining event callbacks, and leveraging idle periods with tools like Web Workers.
What is INP? Breaking Down the Basics
INP decomposes into input delay, processing time, and presentation delay, revealing practical examples of responsive design.
Defining Interaction to Next Paint (INP) in Simple Terms
Interaction to Next Paint (INP) captures website responsiveness by measuring the time between a user’s interaction and the subsequent visual update.[1] Unlike FID, it evaluates every interaction throughout the page’s lifetime, providing a more complete picture of user experience.[2]
The metric focuses on the delay before the next visual frame appears, ensuring that immediate feedback is provided when users click, tap, or type.[1] Starting in March 2024, INP is set to replace FID in Google’s Core Web Vitals framework.[2]
The Three Components: Input Delay, Processing Time, and Presentation Delay
INP is composed of three crucial elements: Input Delay, which measures the latency before the browser starts processing a user interaction;[4] Processing Time, which accounts for the execution duration of event handlers;[1] and Presentation Delay, the interval between processing completion and the actual visual update.[4]
Why INP Offers a More Complete Picture of User Experience Than FID
Unlike FID, which only measures the first interaction delay, INP continuously monitors all user interactions, providing deeper insights into overall site performance.[1] This holistic approach captures the true complexity of user experiences, addressing the shortcomings of FID.[5]
Real-World Examples: What INP Measures in Everyday Browsing
From clicking an “Add to Cart” button to typing in a search box, INP tracks the responsiveness of interactions that matter in everyday browsing, ensuring that visual feedback meets user expectations.[1] It provides actionable insights for optimizing interactions that drive engagement and conversion.[6]
How INP Works and Gets Calculated
INP’s calculation combines input delay, processing time, and presentation delay to reflect true user experience.
The Anatomy of a User Interaction: Clicks, Taps, and Keypresses
User interactions such as clicks, taps, and keypresses initiate a sequence where the browser registers the action, processes it, and then renders visual feedback.[1]
Understanding the Full Interaction Lifecycle
The lifecycle begins with an input delay, proceeds to processing time, and ends with presentation delay. Each phase is critical in determining the overall responsiveness of the page.[1]
The 75th Percentile: How Google Determines Your Final INP Score
Google calculates the INP score based on the 75th percentile of all interactions, ensuring that occasional delays don’t skew the overall performance metric.[1]
INP Scoring Thresholds: Good, Needs Improvement, and Poor Performance
INP scores below 200 milliseconds are considered good, while scores above 500 milliseconds indicate poor responsiveness. This categorization helps in setting performance targets.[4]
INP vs. First Input Delay: Key Differences
A comparison with FID reveals INP’s advantage in capturing ongoing interactions beyond the first user action.
Why FID Only Told Part of the Responsiveness Story
FID measured only the initial interaction, missing the broader experience that users encounter throughout their session.[1]
Continuous Measurement vs. First Interaction: The Major INP Advantage
INP continuously monitors interactions, offering insights that reflect the entire user journey rather than a single moment.[1]
Processing Time: The Critical Component FID Didn’t Account For
By including processing time, INP provides a fuller understanding of the delays caused by event handling and JavaScript execution.[1]
The March 2024 Transition: What It Means for Your Website
The scheduled transition from FID to INP in March 2024 emphasizes the need for comprehensive performance measurement across all user interactions.[13]
Measuring and Monitoring Your Website’s INP
Accurate INP tracking using tools like Chrome DevTools and PageSpeed Insights highlights real user performance.
Using Chrome DevTools to Identify Problematic Interactions
Chrome DevTools can profile interactions, helping developers pinpoint long tasks that block responsiveness.[15]
PageSpeed Insights: Getting Real-User INP Data
PageSpeed Insights combines lab and field data to offer a complete view of how users experience interactions on your site.[16]
Field Data vs. Lab Data: Understanding the Crucial Difference
While lab data provides controlled test results, field data reflects the true performance experienced by real users.[17]
Additional Measurement Tools and APIs for Developers
Beyond native tools, libraries like web-vitals and Lighthouse user flows offer further insights into INP performance.[19]
Common Causes of Poor INP Performance
Heavy JavaScript, inefficient event handlers, and complex DOM updates are identified as key bottlenecks impacting INP.
Heavy JavaScript Execution Blocking the Main Thread
Extensive JavaScript tasks can block the main thread, causing delays in user interaction responses.[22]
Inefficient Event Handlers and Input Processing
Suboptimal event handlers that perform excessive processing can significantly affect INP performance.[9]
Complex DOM Updates and Layout Calculations
Frequent or heavy DOM manipulations trigger costly layout recalculations, hindering quick visual updates.[7]
Third-Party Scripts and Their Impact on INP
External scripts can introduce unexpected delays by adding extra processing overhead and event listeners.[23]
Strategies to Optimize Your Website’s INP
Optimizing INP involves breaking up long tasks, refining event listeners, and leveraging idle periods and Web Workers.
Breaking Up Long-Running JavaScript Tasks
Dividing lengthy tasks into smaller asynchronous operations helps ensure that the main thread remains responsive.[7]
Optimizing Event Listeners for Maximum Responsiveness
Streamlining event handlers and deferring non-critical logic can drastically reduce interaction delays.[7]
Using the Browser’s Idle Periods Effectively
Leveraging idle periods allows deferred tasks to run without disrupting the user experience.[7]
Web Workers and Off-Main-Thread Processing Techniques
Offloading heavy computation to Web Workers keeps the main thread free for handling user interactions efficiently.[7]
- [1] https://web.dev/articles/inp
- [2] https://developer.mozilla.org/en-US/docs/Glossary/Interaction_to_next_paint
- [3] https://www.speedcurve.com/web-performance-guide/understanding-and-improving-interaction-to-next-paint/
- [4] https://www.debugbear.com/docs/metrics/interaction-to-next-paint
- [5] https://www.quattr.com/core-web-vitals/inp-vs-fid
- [6] https://coralogix.com/guides/real-user-monitoring/interaction-to-next-paint-inp-5-ways-optimize/
- [7] https://web.dev/articles/optimize-inp
- [8] https://www.onely.com/blog/what-is-a-good-inp-score/
- [9] https://nitropack.io/blog/post/improve-interaction-to-next-paint-inp
- [10] https://vercel.com/blog/first-input-delay-vs-interaction-to-next-paint
- [11] https://calibreapp.com/blog/interaction-to-next-paint
- [12] https://www.onely.com/blog/difference-between-fid-and-inp/
- [13] https://web.dev/blog/inp-cwv-march-12
- [14] https://www.portent.com/blog/design-dev/interaction-to-next-paint.htm
- [15] https://www.debugbear.com/blog/inp-chrome-devtools
- [16] https://kahunam.com/articles/web-performance/how-to-measure-interaction-to-next-paint/
- [17] https://www.onely.com/blog/measuring-web-performance-lab-vs-field-data/
- [18] https://gtmetrix.com/blog/field-vs-lab-synthetic-data-how-do-they-compare/
- [19] https://developer.chrome.com/blog/inp-tools-2022
- [20] https://codelabs.developers.google.com/measuring-inp
- [21] https://frontendmasters.com/blog/mastering-interaction-to-next-paint-inp/
- [22] https://codelabs.developers.google.com/understanding-inp
- [23] https://www.debugbear.com/blog/inp-misconceptions
- [24] https://sitespeedoptimization.pro/blog/how-to-improve-inp/