INP (INP)

What is Interaction to Next Paint (INP)?

Interaction to Next Paint (INP) is a new Core Web Vital that measures a website's responsiveness to user interactions. Since March 2024, INP has replaced First Input Delay (FID) as the official ranking factor and provides a more comprehensive assessment of a page's interactivity.

Definition and Significance

INP measures the time between a user interaction (click, tap, keyboard input) and the next frame rendered by the browser. This metric captures all interactions during the entire page visit, not just the first one, providing a more realistic picture of the actual user experience.

Why is INP Important?

• Ranking Factor: Official Google ranking factor since March 2024
• User Experience: Direct impact on perceived responsiveness
• Conversion Rate: Slow interactions lead to higher bounce rates
• Mobile Performance: Particularly critical for mobile devices with limited resources

INP Measurement and Thresholds

Measuring INP

INP is measured in milliseconds (ms) and captures:

1. All Interactions: Clicks, taps, keyboard inputs
2. Entire Session: From page load to exit
3. 95th Percentile: The worst value from 95% of interactions

Thresholds

Main Causes of Poor INP Values

1. Long JavaScript Execution Times

Problem: Blocking JavaScript prevents quick responses

Solution:

• Implement code splitting
• Lazy loading for non-critical scripts
• Web Workers for heavy calculations

2. Main Thread Blocking

Problem: CPU-intensive tasks block the main thread

Solution:

• Asynchronous processing
• Use RequestIdleCallback
• Chunking of large data volumes

3. Unoptimized Event Handlers

Problem: Heavy event handlers delay responses

Solution:

• Debouncing and Frequency limiting
• Event delegation
• Passive event listeners

4. Render-Blocking Resources

Problem: CSS and JavaScript delay rendering

Solution:

• Inline Initial CSS
• Load JavaScript asynchronously
• Use Performance hints

INP Optimization: Best Practices

JavaScript Optimization

1. Code Splitting
   • Only load necessary code initially
   • Dynamic imports for features
   • Route-based code splitting
2. Web Workers
   • Offload heavy calculations
   • Image processing in workers
   • Parallelize data processing
3. Event Handler Optimization

   // Debouncing for search functions
   const debouncedSearch = debounce(handleSearch, 300);
   
   // Passive event listeners
   element.addEventListener('scroll', handleScroll, { passive: true });

CSS Optimization

1. Critical CSS
   • Above-the-fold CSS inline
   • Load non-critical CSS asynchronously
   • CSS minification
2. CSS Animations
   • Use transform and opacity
   • Use will-change property
   • Enable GPU rendering

Resource Loading

1. Preloading

   <link rel="preload" href="critical.js" as="script">
   <link rel="preload" href="hero-image.jpg" as="image">

2. Lazy Loading
   • Deferred loading of images and videos
   • Intersection Observer API
   • Progressive enhancement

Tools for INP Measurement

Google Tools

1. Performance Insights
   • Laboratory data for INP
   • Specific optimization suggestions
   • Mobile and desktop analysis
2. Debugging tools
   • Performance tab
   • INP metrics in timeline
   • Bottleneck identification
3. Google Search Console
   • Field data for INP
   • Google Web Vitals report
   • Historical trends

Third-Party Tools

1. WebPageTest
   • Detailed performance analysis
   • Custom test configurations
   • Video recording of interactions
2. GTmetrix
   • Real-time INP measurement
   • Competitor comparison
   • Optimization recommendations

Monitoring and Tracking

Continuous Monitoring

1. Real User Monitoring (RUM)
   • Collect real user data
   • Field data vs. lab data
   • Device and browser-specific analysis
2. Core Web Vitals Dashboard
   • Automatic alerts for degradations
   • Trend analysis over time
   • Segmentation by pages and devices

Performance Budgets

1. Define INP Budgets
   • Maximum INP value per page
   • Warnings when exceeded
   • Integration into CI/CD pipeline
2. Regular Audits
   • Weekly performance reviews
   • A/B tests for optimizations
   • Documentation of improvements

Common INP Problems and Solutions

Problem: Slow Search Function

Symptom: High INP values during search interactions

Solution:

• Implement debouncing (300ms)
• Server-side search for large datasets
• Cache search results

Problem: Heavy Forms

Symptom: Delays during form interactions

Solution:

• Progressive enhancement
• Optimize client-side validation
• Asynchronous form submission

Problem: Image Galleries

Symptom: High INP during image changes

Solution:

• Lazy loading for images
• Preloading next images
• Optimized image formats (WebP, AVIF)

Future of INP Metrics

Developments 2025

1. Extended Metrics
   • Interaction to First Paint (IFP)
   • Interaction to Last Paint (ILP)
   • Interaction Response Time (IRT)
2. AI-Based Optimization
   • Automatic code optimization
   • Predictive performance
   • Intelligent resource loading
3. Mobile-First INP
   • Device-specific thresholds
   • 5G optimizations
   • Progressive Web App metrics