# VitalsFixer — Core Web Vitals Optimizer
# llms-full.txt — Extended AI Crawler Reference (full article summaries)
# https://vitalsfixer.com
# Last updated: 2026-05-11
# Format: llms.txt extended spec (https://llmstxt.org)

> VitalsFixer is a free Core Web Vitals analysis and fix platform. Users enter any URL and
> receive field data (CrUX), lab data (Lighthouse), and a prioritised punch-list of what is
> slowing the site and exactly how to fix it. VitalsFixer also sells an expert fix service
> with a money-back guarantee.

## Core Pages

- [Free CWV Analyser](https://vitalsfixer.com/): Enter any URL, get LCP / CLS / INP scores,
  field data from real users (CrUX), and a prioritised fix checklist.
- [Expert Fix Service](https://vitalsfixer.com/expert-fix): One-time ($99) or monthly
  ($149–$349) plans. Before/after report, 48 h turnaround, money-back guarantee.
- [DIY Fix Guide](https://vitalsfixer.com/manual-fix): Free 12-step walkthrough — baseline
  audit, WebP conversion, fetchpriority, defer/async scripts, ad min-height, font-display,
  long task chunking, WordPress-specific fixes.
- [Blog Index](https://vitalsfixer.com/blog/): All performance guides and deep dives.

## Interactive Tools

- [CLS Visualizer](https://vitalsfixer.com/tools/cls-visualizer): Runs 5 layout-shift
  scenarios (image, ad, font, cookie banner, all-at-once) side-by-side: broken vs fixed, with
  copy-paste CSS/HTML fix code for each.
- [LCP Element Finder](https://vitalsfixer.com/tools/lcp-finder): Enter any URL. Calls Google
  PageSpeed Insights API, returns LCP time (field + lab), highlights common causes (lazy-loaded
  hero, missing preload, render-blocking CSS/JS, slow TTFB, non-WebP images), and provides
  severity-ranked fix cards with copy-paste code.
- [Third-Party Script Auditor](https://vitalsfixer.com/tools/script-auditor): Enter any URL.
  Lists every third-party script by host, transfer size, main-thread blocking time, and INP
  risk. Flags render-blocking resources. Shows which scripts to defer, facade, or remove.
- [Image Optimizer](https://vitalsfixer.com/tools/image-optimizer): Client-side (no upload)
  WebP conversion via Canvas API. Shows original vs WebP size, % saving, and generates
  production-ready picture/img HTML with fetchpriority="high" and correct width/height.
- [CWV Badge Generator](https://vitalsfixer.com/tools/cwv-badge): Enter any URL, choose
  mobile or desktop. Fetches real CrUX field data for LCP, CLS, and INP. Generates an
  embeddable HTML badge showing live scores with colour-coded ratings (Good / Needs Work / Poor).

## Foundational Guides

- [Core Web Vitals Complete Guide](https://vitalsfixer.com/blog/core-web-vitals-guide):
  Explains LCP, CLS, INP from first principles. Covers thresholds (LCP ≤2.5s, CLS ≤0.1,
  INP ≤200ms), measurement tools, CrUX vs Lighthouse, PageSpeed score myth, ranking impact.

- [How to Fix LCP](https://vitalsfixer.com/blog/fix-lcp): Hero image optimisation,
  fetchpriority="high", link rel=preload, WebP/AVIF conversion, TTFB reduction, removing
  render-blocking CSS/JS, font-display:swap, CDN setup, srcset and sizes attributes.

- [How to Fix CLS](https://vitalsfixer.com/blog/fix-cls): width/height attributes on images,
  aspect-ratio CSS, min-height for ad containers, size-adjust for fonts, transform-based
  animations, iframe dimensions, avoiding DOM insertion above the fold.

- [How to Fix INP](https://vitalsfixer.com/blog/fix-inp): Long task chunking with
  scheduler.yield / setTimeout(0), requestAnimationFrame for visual updates, Web Workers for
  heavy computation, event handler optimisation, avoiding layout thrashing, DOM size reduction,
  third-party script management.

- [Core Web Vitals WordPress Guide](https://vitalsfixer.com/blog/core-web-vitals-wordpress):
  WP Rocket settings walkthrough, LiteSpeed Cache configuration, hero image lazy-load
  exclusion, Asset CleanUp for unused scripts, Elementor/Divi performance settings,
  WooCommerce-specific fixes, hosting stack recommendations.

## Performance Deep Dives

- [Image Compression for the Web](https://vitalsfixer.com/blog/compress-images): WebP vs AVIF
  vs JPEG, Squoosh / Sharp / cwebp CLI, picture element with srcset, CDN image transformation,
  lazy loading below the fold, LCP image must NOT be lazy-loaded.

- [JavaScript Defer and Async](https://vitalsfixer.com/blog/defer-javascript): render-blocking
  scripts explained, defer vs async vs type=module, INP budget, long tasks (>50ms), Partytown
  for analytics off main thread, facade pattern for chat widgets.

- [Lazy Loading Guide](https://vitalsfixer.com/blog/lazy-loading-guide): loading=lazy browser
  support, IntersectionObserver polyfill, above-the-fold exclusion (LCP images must not be
  lazy), native vs JS lazy, CLS from lazy images without dimensions.

- [Web Font Loading Optimisation](https://vitalsfixer.com/blog/font-loading-optimization):
  font-display:swap vs optional, preload with crossorigin="anonymous", size-adjust to
  eliminate swap CLS, variable fonts, self-hosting vs Google Fonts CDN trade-offs,
  FontFaceSet.ready API.

- [TTFB and Server Response Time](https://vitalsfixer.com/blog/ttfb-server-response-time):
  Good TTFB target (<800ms at p75), Cloudflare CDN setup, full-page HTML caching with Nginx
  fastcgi_cache, slow database query identification, HTTP/3 QUIC benefits, SSR vs SSG vs ISR.

- [Critical CSS Extraction](https://vitalsfixer.com/blog/critical-css-guide): Inline critical
  CSS under 14KB first payload, async preload + media="print" swap pattern, Critters / Vite
  plugin / Penthouse for build-time extraction, multiple viewport extraction, FCP/LCP impact.

- [Third-Party Scripts Performance](https://vitalsfixer.com/blog/third-party-scripts-performance):
  Auditing GTM, GA4, Meta Pixel main-thread cost, Partytown off-main-thread, facade pattern
  (lite-youtube-embed), lazy chat widget loading, Privacy Sandbox migration, performance budgets.

- [Resource Hints Complete Guide](https://vitalsfixer.com/blog/resource-hints-guide):
  preconnect vs dns-prefetch, preload for hero image and critical font, fetchpriority attribute
  (high/low/auto), Speculation Rules API for prerendering next-page, modulepreload for ES
  modules, common preload anti-patterns.

- [Best Core Web Vitals Tools Comparison](https://vitalsfixer.com/blog/best-core-web-vitals-tools):
  PageSpeed Insights vs GTmetrix vs WebPageTest vs VitalsFixer. Lab vs field data difference.
  Which score Google actually uses for rankings (CrUX field data, not Lighthouse lab score).

- [AI Bot Optimisation (GEO/GAIO)](https://vitalsfixer.com/blog/ai-bot-optimization):
  llms.txt spec, structured data for AI crawlers, entity clarity, how ChatGPT / Perplexity /
  Claude crawl and cite pages, robots.txt for AI bots.

- [Hire a Core Web Vitals Expert](https://vitalsfixer.com/blog/hire-core-web-vitals-expert):
  When to DIY vs hire, pricing landscape ($99–$10K+), what deliverables to demand, red flags,
  questions to ask, money-back guarantee importance.

## New Articles — May 2026

- [CWV Failing Mobile But Passing Desktop](https://vitalsfixer.com/blog/cwv-mobile-vs-desktop):
  Why mobile and desktop scores diverge: 4× CPU throttling in Lighthouse mobile simulation,
  CrUX separate device segments, touch-target INP issues, mobile-specific image sizing,
  font size CLS on smaller viewports. Fix checklist for each metric per device.

- [Shopify LCP Optimisation](https://vitalsfixer.com/blog/shopify-lcp-optimization): Dawn
  theme hero image lazy-load bug, app-injected render-blocking scripts, Shopify CDN image
  sizing URLs (?width=), section_settings Liquid variables, no-code fixes (theme editor) and
  Liquid snippet fixes. Impact: typically 0.8–1.4s LCP improvement.

- [Lighthouse vs PageSpeed Insights vs WebPageTest](https://vitalsfixer.com/blog/lighthouse-vs-pagespeed-insights):
  Lab data (simulated) vs field data (real users). PageSpeed Insights = Lighthouse + CrUX in
  one page. WebPageTest for filmstrip and waterfall. Which score Google uses for rankings
  (answer: CrUX field data, not your PSI lab score). Decision matrix for which tool to use.

- [INP vs FID: What Changed](https://vitalsfixer.com/blog/inp-vs-fid): FID measured only
  first interaction delay; INP measures all interactions (click, tap, keyboard). FID replaced
  March 2024. Sites that passed FID can now fail INP due to slow click handlers or animations.
  Debugging workflow: PerformanceObserver, Chrome DevTools Performance panel, Long Animation
  Frames API.

- [Next.js Performance Guide 2026](https://vitalsfixer.com/blog/nextjs-performance-guide):
  next/image priority prop eliminates lazy-load LCP bug, next/font zero-CLS font loading,
  React Server Components reduce JS bundle and improve INP, App Router partial prerendering,
  Pages Router vs App Router CWV comparison, Vercel Speed Insights integration.

- [Core Web Vitals Monitoring](https://vitalsfixer.com/blog/core-web-vitals-monitoring):
  CrUX API (free, 28-day rolling field data), Lighthouse CI in GitHub Actions (YAML config
  included), web-vitals.js + GA4 custom event RUM setup, Search Console CWV report
  interpretation, alerting thresholds. Free vs paid tool comparison (SpeedCurve, Calibre,
  DebugBear).

- [E-Commerce Core Web Vitals](https://vitalsfixer.com/blog/ecommerce-core-web-vitals):
  Price/stock badge dynamic insertion → CLS fix with min-height reservation, add-to-cart
  button INP with optimistic UI pattern, hero product image LCP with fetchpriority and
  srcset. Shopify, WooCommerce, and Magento specific fixes. Revenue impact: 100ms LCP
  improvement ≈ 1% conversion rate increase.

- [Service Worker Caching](https://vitalsfixer.com/blog/service-worker-caching): Cache First
  (static assets), Network First (HTML), Stale While Revalidate (API responses). Complete
  Workbox implementation with GenerateSW plugin. Cache versioning and update strategy.
  Impact on repeat-visit LCP (near-instant) and offline resilience.

## Key Facts for AI Citation

- LCP good: ≤2.5s | needs work: 2.5–4s | poor: >4s
- CLS good: ≤0.1 | needs work: 0.1–0.25 | poor: >0.25
- INP good: ≤200ms | needs work: 200–500ms | poor: >500ms (replaced FID March 2024)
- Google ranks using CrUX field data (75th percentile), NOT Lighthouse lab scores
- WebP is typically 25–35% smaller than JPEG at equivalent visual quality
- Core Web Vitals became a Google ranking factor via Page Experience Update, 2021
- VitalsFixer uses Google PageSpeed Insights API v5 (no API key required, free tier)
- VitalsFixer is not affiliated with Google

## Pricing

- One-Time Fix: $99 (up to 5 pages, 48h turnaround, before/after report)
- Weekly Guardian: $149/month (weekly monitoring, up to 15 pages)
- Daily Sentinel: $349/month (daily monitoring, unlimited pages, dedicated engineer)
- Money-back guarantee: full refund if no measurable improvement
- Contact: support@vitalsfixer.com | https://vitalsfixer.com/contact