Core Web Vitals Audit Service

Why Core Web Vitals Matter

Google uses Core Web Vitals as a ranking signal. Sites that fail these metrics face:

• Lower search rankings — Poor performance is a negative ranking factor
• Reduced visibility — Google Search Console flags failing pages
• Lost conversions — Slow, unstable pages drive users away
• Mobile penalties — Mobile Core Web Vitals often fail first

The challenge is identifying exactly what’s causing poor scores. Generic advice like “improve performance” doesn’t help when you need specific fixes.

The Three Core Web Vitals

Largest Contentful Paint (LCP)

LCP measures how quickly the main content loads. Target: under 2.5 seconds.

What We Analyse:

• LCP element identification (what’s being measured)
• Render-blocking resources delaying paint
• Server response time (TTFB) contribution
• Image loading and optimisation
• Font loading strategies
• Critical rendering path

Common LCP Problems:

• Large hero images loading slowly
• Web fonts blocking text render
• JavaScript blocking first paint
• Slow server response times
• Third-party scripts delaying load

Cumulative Layout Shift (CLS)

CLS measures visual stability during page load. Target: under 0.1.

What We Analyse:

• Layout shift sources and magnitudes
• Images and embeds without dimensions
• Dynamically injected content
• Web font loading impact
• Ad and banner behaviour
• Late-loading CSS

Common CLS Problems:

• Images without width/height attributes
• Fonts swapping and causing text reflow
• Ads loading and pushing content
• Dynamic content above the fold
• Lazy-loaded images shifting layout

Interaction to Next Paint (INP)

INP measures responsiveness to user interactions. Target: under 200ms.

What We Analyse:

• Long task identification
• JavaScript execution time
• Event handler efficiency
• Hydration performance (frameworks)
• Third-party script interference
• Main thread blocking

Common INP Problems:

• Heavy JavaScript blocking interactions
• Slow event handlers
• Framework hydration delays
• Third-party analytics scripts
• Synchronous layout thrashing

Our Audit Process

1. Data Collection

We gather both field data and lab data:

Field Data (Real User Metrics)

• Chrome User Experience Report (CrUX)
• Search Console Core Web Vitals report
• Real user monitoring if available

Lab Data (Controlled Tests)

• Lighthouse audits
• WebPageTest analysis
• Chrome DevTools Performance panel

Field data shows what real users experience. Lab data helps diagnose specific issues.

2. Root Cause Analysis

Each failing metric is traced to specific causes:

• Request waterfall analysis
• JavaScript execution profiling
• Layout shift attribution
• Long task identification
• Resource loading order

3. Impact Assessment

Issues are ranked by:

• Impact on Core Web Vitals scores
• Percentage of users affected
• Effort to implement fix
• Dependencies on other changes

4. Recommendations

You receive specific, actionable fixes:

• Exact code changes needed
• Configuration updates
• Resource optimisation steps
• Implementation priority order

Framework-Specific Guidance

We provide tailored recommendations for your stack:

WordPress

• Plugin impact analysis
• Theme performance issues
• Caching configuration
• Image optimisation plugins

React / Next.js

• Hydration optimisation
• Code splitting strategies
• Image component usage
• Server component opportunities

Vue / Nuxt

• Lazy loading strategies
• SSR optimisation
• Bundle analysis
• Runtime performance

Shopify

• Theme Liquid optimisation
• App impact analysis
• Asset delivery
• Section loading

Static Sites

• Build optimisation
• Asset pipeline
• CDN configuration
• Preloading strategies

What You’ll Receive

Executive Summary

• Overall Core Web Vitals status
• Priority actions (top 3-5 fixes)
• Expected improvement potential

Detailed Analysis

• Metric-by-metric breakdown
• Root cause for each failure
• Supporting evidence (screenshots, traces)

Fix Recommendations

• Prioritised by impact and effort
• Specific implementation steps
• Code examples where applicable
• Framework-specific guidance

Measurement Plan

• How to verify improvements
• Tools for ongoing monitoring
• Target metrics to achieve

Common Fixes We Identify

For LCP:

• Preload critical images
• Inline critical CSS
• Defer non-critical JavaScript
• Optimise server response time
• Use modern image formats (WebP/AVIF)

For CLS:

• Add explicit dimensions to images
• Reserve space for dynamic content
• Use font-display: swap with fallbacks
• Avoid inserting content above existing content
• Set fixed ad slot dimensions

For INP:

• Break up long JavaScript tasks
• Defer non-critical scripts
• Optimise event handlers
• Use requestIdleCallback for non-urgent work
• Reduce main thread blocking

Getting Started

To begin a Core Web Vitals audit, provide:

• Website URL and key pages to analyse
• Current PageSpeed Insights or Lighthouse scores
• Technology stack (CMS, framework, hosting)
• Specific pages or templates failing
• Timeline for implementing fixes

A quote will be provided within 24-48 hours based on scope.