INP (Interaction to Next Paint) is a Core Web Vital that measures responsiveness by tracking the delay between user interactions and visual feedback. It replaced FID () as a Core Web Vital in March 2024 because it provides a more complete picture of page interactivity.
How INP Works
INP observes all interactions during a page visit, including clicks, taps, and keyboard inputs. For each interaction, it measures the time from when the user initiates the action until the browser paints the next frame showing a visual response.
Unlike FID which only measured the first interaction, INP tracks every interaction throughout the page lifecycle. It then reports the worst interaction latency observed. For pages with many interactions (over 50), it may report a near-worst value to reduce the impact of outliers.
INP Thresholds
Google defines these thresholds for INP scores:
- Good: 200 milliseconds or less
- Needs Improvement: Between 200 and 500 milliseconds
- Poor: Greater than 500 milliseconds
To pass assessment, at least 75% of page visits must have an INP of 200ms or less.
Common Causes of Poor INP
Long JavaScript tasks block the main thread and delay response to user input. Heavy event handlers that run synchronous code prevent the browser from painting updates quickly. Excessive DOM size increases the time needed to process changes and render new frames. competing for main thread resources also contribute to poor INP scores.
Measuring INP
Field data from real users provides the most accurate INP measurements. Google Search Console, PageSpeed Insights, and the Chrome User Experience Report all provide INP data. For lab testing, Chrome DevTools and Lighthouse can simulate interactions, though field data better represents actual user experience.
