Core Web Vitals: A Practical Performance Checklist

Understanding Core Web Vitals

Core Web Vitals are a set of specific factors that Google considers important in a webpage's overall user experience. These metrics focus on loading performance, interactivity, and visual stability of web pages.

The Three Core Metrics

**Largest Contentful Paint (LCP)** - Measures loading performance

Target: < 2.5 seconds

Measures when the largest content element becomes visible

**First Input Delay (FID)** - Measures interactivity

Target: < 100 milliseconds

Measures responsiveness to user interactions

**Cumulative Layout Shift (CLS)** - Measures visual stability

Target: < 0.1

Measures unexpected layout shifts during page load

Why Core Web Vitals Matter

These metrics directly impact:

**Search rankings** - Google uses CWV in ranking algorithms

**User experience** - Faster, more stable sites convert better

**Business metrics** - Improved performance drives revenue

**Mobile experience** - Especially critical for mobile users

What Matters for Core Web Vitals

Focus on the critical rendering path, image optimization, and script management.

Loading Performance (LCP)

**Server Response Time**

Use CDN for static assets

Implement caching strategies

Optimize database queries

Use efficient hosting solutions

**Resource Load Times**

Compress text resources

Remove unused code

Minimize main thread work

Optimize critical rendering path

**Render Blocking Resources**

Minimize CSS and JavaScript

Defer non-critical resources

Use async/await for scripts

Optimize font loading

Interactivity (FID)

**JavaScript Execution**

Break up long tasks

Use web workers for heavy computation

Optimize third-party scripts

Minimize main thread blocking

**Input Responsiveness**

Avoid long-running JavaScript

Use passive event listeners

Optimize event handlers

Reduce render-blocking scripts

Visual Stability (CLS)

**Layout Shifts**

Include size attributes on images

Reserve space for dynamic content

Avoid inserting content above existing content

Use CSS aspect-ratio for responsive images

Quick Wins for Immediate Impact

**Serve modern image formats** - AVIF/WebP with fallbacks

**Preload critical fonts** - Prevent layout shifts

**Remove render-blocking scripts** - Improve initial load

**Optimize largest content elements** - Focus on LCP

**Use proper image dimensions** - Prevent CLS issues

Advanced Optimization Techniques

**Image Optimization**

Implement responsive images

Use modern formats (WebP, AVIF)

Lazy load below-the-fold images

Optimize image compression

**Font Loading Strategy**

Use font-display: swap

Preload critical fonts

Self-host fonts when possible

Minimize font variations

**JavaScript Optimization**

Code splitting and lazy loading

Tree shaking unused code

Minimize bundle sizes

Use efficient libraries

**CSS Optimization**

Minimize CSS delivery

Avoid @import statements

Use CSS Grid and Flexbox efficiently

Optimize animations and transitions

Monitoring and Measurement

**Tools for Tracking CWV**

Google PageSpeed Insights

Chrome DevTools

Web Vitals JavaScript library

Google Search Console

**Real User Monitoring**

Implement performance monitoring

Track field data vs lab data

Monitor across different devices

Set up alerts for regressions

Implementation Roadmap

**Phase 1: Assessment**

Audit current performance

Identify critical issues

Set baseline metrics

Prioritize improvements

**Phase 2: Quick Wins**

Implement image optimization

Fix render-blocking resources

Optimize fonts and CSS

Address layout shifts

**Phase 3: Advanced Optimization**

Code splitting and lazy loading

Service worker implementation

Advanced caching strategies

Continuous monitoring

Common Mistakes to Avoid

**Focusing only on lab data** - Real user metrics matter more

**Ignoring mobile performance** - Mobile is critical for rankings

**Over-optimization** - Balance performance with functionality

**Neglecting monitoring** - Performance requires ongoing attention

Business Impact

**Conversion Optimization**

Faster sites convert better

Improved user experience drives revenue

Better search rankings increase traffic

Enhanced mobile experience boosts engagement

**Technical Benefits**

Reduced bounce rates

Improved user satisfaction

Better SEO performance

Enhanced developer experience

> Faster pages convert better—measure with real user metrics and focus on the critical 2.5-second window for optimal user experience.