Interaction to Next Paint (INP) Issues

What This Means

Interaction to Next Paint (INP) is a Core Web Vital metric that measures page responsiveness by observing the latency of all user interactions throughout the page lifecycle. INP reports the longest interaction latency, representing the worst-case user experience when interacting with the page.

A good INP score is 200ms or less. Poor INP indicates:

• Slow response to user clicks, taps, or keyboard inputs
• Long-running JavaScript blocking the main thread
• Heavy DOM manipulation causing slow visual updates
• Unoptimized event handlers causing delays

Poor INP directly impacts user experience and SEO rankings.

How to Diagnose

Chrome DevTools

• Use Performance panel to record interactions
• Enable "Web Vitals" in the Performance panel
• Look for long tasks (>50ms) during interactions
• Check for layout shifts and style recalculations

Real User Monitoring

// Measure INP using web-vitals library
import {onINP} from 'web-vitals';

onINP(({name, value, rating, entries}) => {
  console.log('INP:', value, rating);
  entries.forEach(entry => {
    console.log('Interaction:', entry.name, entry.duration);
  });
});

Tools

• Chrome User Experience Report (CrUX) for field data
• Lighthouse (Lab data, may not capture real INP)
• WebPageTest for detailed interaction analysis
• Chrome DevTools Performance Insights

Common Culprits

• Heavy JavaScript execution during interactions
• Excessive DOM nodes (>1500 elements)
• Forced synchronous layouts (layout thrashing)
• Large bundle sizes causing parsing delays

General Fixes

1. Break up long tasks - Use setTimeout or requestIdleCallback to yield to the main thread
2. Debounce and throttle event handlers - Limit the frequency of expensive operations during interactions
3. Optimize JavaScript execution - Reduce script evaluation time and avoid blocking work
4. Use web workers - Offload heavy computations to background threads
5. Minimize DOM size - Reduce the number of DOM nodes to speed up rendering
6. Optimize event handlers - Remove unnecessary event listeners and make handlers lightweight
7. Implement code splitting - Load JavaScript on demand to reduce initial parse time
8. Use CSS containment - Apply contain: layout style paint to limit rendering scope
9. Avoid forced synchronous layouts - Batch DOM reads and writes separately
10. Use content-visibility - Defer rendering of off-screen content

Platform-Specific Guides

Further Reading

• web.dev: Optimize INP
• web.dev: What is INP?
• Chrome DevTools: Performance Insights
• web-vitals Library
• Interaction to Next Paint Deep Dive