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INP Optimization - Fundamentals and Best Practices 2025

Interaction to Next Paint (INP) is a new Core Web Vital metric that Google has been using as an official ranking factor since March 2024. INP measures a website's response time to user interactions and replaces the previous First Input Delay (FID) metric.

What is INP (Interaction to Next Paint)?

Definition and Measurement

INP captures the time between a user interaction (click, keypress, touch) and the next frame that is rendered. The metric considers all interactions on a page and returns the 95th percentile value.

Measurement Values:

  • Good: ≤ 200ms
  • Needs Improvement: 200-500ms
  • Poor: > 500ms

Why is INP Important for SEO?

Ranking Factor Since 2024

INP has been an official Google ranking factor since March 2024 and is part of the Core Web Vitals. Websites with poor INP values can be penalized in search results.

User Experience Impact

INP and Conversion Rate

Studies show: 100ms improvement in INP leads to 1% higher conversion rate

Mobile-First Importance

Since INP is particularly critical on mobile devices, the metric gains importance through mobile-first indexing.

Common Causes of Poor INP Values

JavaScript Performance Issues

Main Causes:

  1. Heavy JavaScript Bundles - Large, unoptimized JS files
  2. Blocking JavaScript - Scripts that block rendering
  3. Inefficient Event Handlers - Poorly optimized event listeners
  4. Memory Leaks - Memory leaks in JavaScript code

Rendering Problems

Layout Shifts and Reflows:

  • Dynamic content without reserved space
  • Font loading without fallback
  • Images without defined dimensions

Third-Party Scripts

Performance Killers:

  • Analytics tools (Google Analytics, Facebook Pixel)
  • Advertising scripts
  • Chat widgets
  • Social media embeds

INP Optimization: Practical Measures

1. JavaScript Optimization

Implement Code Splitting:

// Lazy loading for non-critical components
const LazyComponent = React.lazy(() => import('./LazyComponent'));

Optimize Event Handlers:

  • Debouncing for frequent events
  • Throttling for scroll events
  • Use event delegation

2. Rendering Optimization

Optimize Critical Rendering Path:

  • Inline critical CSS
  • Load non-critical CSS asynchronously
  • Place JavaScript at the end of the page

Ensure Layout Stability:

  • Images with defined dimensions
  • Use font-display: swap
  • Use CSS containment

3. Optimize Third-Party Scripts

Lazy Loading for External Scripts:

<script>
  // Load script only after user interaction
  document.addEventListener('click', function() {
    loadThirdPartyScript();
  }, { once: true });
</script>

Asynchronous Integration:

  • Load scripts with async or defer
  • Use non-blocking analytics
  • Implement conditional loading

INP Monitoring and Testing

Tools for INP Measurement

Google Tools:

  • PageSpeed Insights - Lab data for INP
  • Search Console - Field data for INP
  • Chrome DevTools - Performance tab

Third-Party Tools:

  • WebPageTest - Detailed performance analysis
  • GTmetrix - INP monitoring
  • Lighthouse - Automated audits

Monitoring Strategy

Continuous Monitoring:

  1. Weekly INP checks for critical pages
  2. Automated alerts for INP deterioration
  3. A/B testing for performance changes

INP Optimization Checklist

Technical Optimizations

  • Analyze JavaScript bundles and optimize
  • Implement code splitting
  • Optimize event handlers (Debouncing/Throttling)
  • Inline critical CSS
  • Load non-critical CSS asynchronously
  • Lazy load third-party scripts
  • Images with defined dimensions
  • Fonts with font-display: swap

Monitoring and Testing

  • Document INP baseline in Search Console
  • Check PageSpeed Insights regularly
  • Perform Chrome DevTools performance audits
  • Use WebPageTest for detailed analysis
  • Set up monitoring alerts

Common INP Problems and Solutions

Problem: Heavy JavaScript Bundles

Symptoms:

  • High INP values (>500ms)
  • Slow interactions
  • Blocking JavaScript

Solutions:

  • Bundle analysis with Webpack Bundle Analyzer
  • Implement code splitting
  • Optimize tree shaking
  • Remove unused code

Problem: Third-Party Script Overhead

Symptoms:

  • INP spikes during script loading
  • Blocking of user interactions
  • High memory usage

Solutions:

  • Conditional loading
  • Script prioritization
  • CDN optimization
  • Implement lazy loading

INP vs. Other Core Web Vitals

Metric
Measures
Importance
Optimization
LCP
Largest Contentful Paint
Loading Performance
Images, Fonts, CSS
FID
First Input Delay
Interactivity (deprecated)
JavaScript Optimization
INP
Interaction to Next Paint
Interactivity (current)
Event Handlers, Rendering
CLS
Cumulative Layout Shift
Visual Stability
Layout Stability

Future of INP Optimization

Web Vitals Evolution

Google continuously develops new metrics. INP is the current standard, but other metrics like Time to Interactive (TTI) and Total Blocking Time (TBT) remain relevant.

AI and Performance

Machine Learning in Performance:

  • Automatic code optimization
  • Predictive performance monitoring
  • Intelligent resource loading

Related Topics

Last Update: October 21, 2025