Interaction to Next Paint (INP)

What is Interaction to Next Paint (INP)?

Definition and Importance

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 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

INP Measurement

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 fast 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 datasets

3. Unoptimized Event Handlers

Problem: Heavy event handlers delay responses

Solution:

• Debouncing and throttling
• Event delegation
• Passive event listeners

4. Render-Blocking Resources

Problem: CSS and JavaScript delay rendering

Solution:

• Inline critical CSS
• Load JavaScript asynchronously
• Use resource hints

INP Optimization: Best Practices

JavaScript Optimization

1. Code Splitting

• Load only 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

• Inline above-the-fold CSS
• Load non-critical CSS asynchronously
• CSS minification

2. CSS Animations

• Use transform and opacity
• Use will-change property
• Enable hardware acceleration

Resource Loading

1. Preloading

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

2. Lazy Loading

• Defer loading of images and videos
• Intersection Observer API
• Progressive enhancement

Tools for INP Measurement

Google Tools

1. PageSpeed Insights

• Lab data for INP
• Specific optimization suggestions
• Mobile and desktop analysis

2. Chrome DevTools

• Performance tab
• INP metrics in timeline
• Bottleneck identification

3. Google Search Console

• Field data for INP
• Core 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 on degradation
• Trend analysis over time
• Segmentation by pages and devices

Performance Budgets

1. Define INP Budgets

• Maximum INP value per page
• Warnings on threshold exceedance
• 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
• Preload next images
• Optimized image formats (WebP, AVIF)

Future of INP Metrics

2025 Developments

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

Related Topics

• Core Web Vitals Overview
• Largest Contentful Paint (LCP)
• Cumulative Layout Shift (CLS)
• Page Speed & Performance
• JavaScript SEO