The Ultimate Checklist for Improving Core Web Vitals in 2025

Core Web Vitals: The 2025 Reality

Since becoming official ranking factors in 2021, Core Web Vitals have become essential for SEO success. In 2025, the competition is fiercer than ever, and websites with poor Core Web Vitals scores are losing significant traffic.

Performance Benchmarks

LCP

under 2.5 seconds

Largest Contentful Paint

FID

under 100ms

First Input Delay

CLS

under 0.1

Cumulative Layout Shift

Largest Contentful Paint (LCP) Optimization

LCP measures loading performance. It marks the point when the largest image or text block visible within the viewport is fully rendered. To provide good user experience, LCP should occur within 2.5 seconds of when the page first starts loading.

LCP Checklist

Image Optimization

Optimize hero images (under 200KB)
Use responsive images with srcset
Implement WebP/AVIF formats
Add preload hints for critical images
Set proper width and height attributes
Use modern lazy loading for below-fold images

Server Performance

Optimize Time to First Byte (under 200ms)
Implement CDN for static assets
Enable server-side caching
Use HTTP/2 or HTTP/3
Minimize server response times
Optimize database queries

Pro Tip: Preload Critical Resources

Use resource hints to prioritize loading of critical assets. Add `<link rel="preload">` for your hero image and critical CSS to improve LCP scores significantly.

First Input Delay (FID) Optimization

FID measures interactivity. It quantifies the experience users feel when trying to interact with unresponsive pages. To provide good user experience, pages should have FID of 100 milliseconds or less.

FID Checklist

JavaScript Optimization

Split large JavaScript bundles
Use code splitting for routes
Implement tree shaking
Minimize main thread work
Remove unused polyfills
Use Web Workers for heavy tasks

Third-Party Scripts

Audit all third-party scripts
Load analytics asynchronously
Defer chat widgets
Remove unnecessary plugins
Use facade loading for heavy widgets
Implement resource loading budgets

FID Optimization Impact

Before Optimization

Long main thread blocking
Delayed user interactions
Poor responsiveness scores
Higher bounce rates

After Optimization

Faster response to clicks
Smooth user interactions
Better engagement metrics
Improved conversion rates

Cumulative Layout Shift (CLS) Optimization

CLS measures visual stability. It quantifies how much unexpected layout shift occurs during the entire lifespan of the page. To provide good user experience, pages should maintain CLS of 0.1 or less.

CLS Checklist

Layout Stability

Set width/height on all images
Use aspect-ratio CSS property
Reserve space for videos/iframes
Optimize web font loading
Avoid inserting content above existing content
Reserve space for ads
Use transforms for animations
Test banner/notification layouts

Common CLS Mistake

Never insert content above existing content unless it's in response to user interaction. This includes ads, banners, forms, and any dynamic content that pushes existing content down.

Testing and Monitoring Tools

Essential Testing Tools

PageSpeed Insights: Official Google scoring with real user data
Search Console: Real user metrics from your actual visitors
WebPageTest: Detailed performance analysis with waterfall charts
Chrome DevTools: Local testing and debugging capabilities
WebEvo.ai: Comprehensive Core Web Vitals analysis with actionable insights

Core Web Vitals Testing Process

Baseline Assessment

Run initial tests using PageSpeed Insights and WebEvo.ai to establish current Core Web Vitals scores.

Identify Priority Issues

Focus on the metrics with the worst scores first. Usually start with LCP as it has the biggest impact.

Implement Optimizations

Apply targeted fixes based on the specific issues identified in your analysis.

Monitor and Iterate

Set up ongoing monitoring to track improvements and catch any regressions in performance.

Your 30-Day Core Web Vitals Action Plan

Week-by-Week Improvement Strategy

Week 1: LCP Foundation

Focus on image optimization, server response times, and critical resource loading. These changes typically yield the biggest improvements.

Week 2: FID Enhancement

Optimize JavaScript, implement code splitting, and audit third-party scripts to improve interactivity scores.

Week 3: CLS Stability

Address layout shifts by setting image dimensions, optimizing fonts, and testing dynamic content insertion.

Week 4: Testing and Monitoring

Set up comprehensive monitoring, validate improvements with real user data, and create maintenance processes.

Success Metrics

Target green scores across all three Core Web Vitals: LCP under 2.5s, FID under 100ms, and CLS under 0.1. Monitor both lab data and real user metrics for comprehensive assessment.

Core Web Vitals optimization is not a one-time task—it's an ongoing commitment to user experience and search performance. Regular monitoring and continuous improvement ensure your website stays competitive in search rankings while providing an excellent user experience.