What Does Site Audit Catch That Lighthouse Misses?

Lighthouse is excellent for: Performance optimization, Core Web Vitals, basic accessibility

Lighthouse is NOT designed for: Schema optimization, advanced accessibility (WCAG 2.1 AA), real device testing, social sharing validation, site-wide crawling

Here’s what Scan catches that Lighthouse doesn’t.

---

The 5 Categories Lighthouse Misses

1. Schema Markup Optimization (Not Just Validation)

What Lighthouse checks:

• Does structured data exist? (Yes/No)
• Is the JSON-LD syntax valid?

What Lighthouse doesn’t check:

• Is the schema strategically optimized for rich results?
• Are you missing schema types that would improve CTR?
• Is the schema complete with all recommended fields?

---

Real example:

Your schema (passes Lighthouse):

{
  "@type": "Organization",
  "@context": "https://schema.org",
  "name": "Acme Corp",
  "url": "https://www.acmecorp.com"
}

Lighthouse: “Structured data is valid”

What Lighthouse missed:

You’re missing:

• LocalBusiness schema (enables map pack, business hours in SERPs)
• aggregateRating (enables star ratings in search results)
• BreadcrumbList schema (enables breadcrumb trails in SERPs)
• FAQPage schema (enables FAQ rich snippets)

Scan catches this:

Missing LocalBusiness schema
   Impact: Not eligible for map pack, missing business hours in SERPs
   Fix: Add LocalBusiness schema with address, phone, geo coordinates

Missing aggregateRating
   Impact: No star ratings displayed in search results
   Fix: Add aggregateRating with ratingValue and reviewCount

Missing BreadcrumbList schema
   Impact: Google shows full URL instead of breadcrumb trail
   Fix: Add BreadcrumbList schema to navigation

CTR impact: Sites with rich snippets (stars, breadcrumbs, business hours) get 20-30% higher CTR than sites without.

---

2. Advanced Accessibility (150+ WCAG Checks vs 50)

What Lighthouse checks: about 50 automated accessibility rules (via axe-core)

What Scan checks: 150+ WCAG 2.1 AA rules (via pa11y)

---

Real example:

Lighthouse accessibility score: 100/100

Scan pa11y audit found:

1. Missing aria-label on icon-only buttons (WCAG 4.1.2)

   <!-- Lighthouse missed this -->
   <button><i class="icon-search"></i></button>
   
   <!-- Should be -->
   <button aria-label="Search"><i class="icon-search"></i></button>

2. Insufficient color contrast on disabled form fields (WCAG 1.4.3)

   • Lighthouse only checks enabled form fields
   • Disabled button had 3.5:1 contrast (minimum: 4.5:1)

3. Form labels not programmatically associated with inputs (WCAG 1.3.1)

   <!-- Lighthouse missed this -->
   <label>Email</label>
   <input type="email" />
   
   <!-- Should be -->
   <label for="email">Email</label>
   <input id="email" type="email" />

4. Missing focus indicators on custom dropdowns (WCAG 2.4.7)

   • outline: none on focused elements
   • Keyboard users couldn’t see focus state

Why Lighthouse missed these: Lighthouse runs about 50 checks. pa11y runs about 150+ checks. Many accessibility issues require context-specific analysis that Lighthouse’s automated rules don’t cover.

Impact: 15-20% of web users have accessibility needs. These issues block screen reader users from completing forms and keyboard users from navigating.

---

3. Real Device Testing (iOS Safari, Android Chrome)

What Lighthouse checks: Mobile-friendly test based on Chrome’s mobile simulator

What Scan checks: Real device testing on iOS Safari and Android Chrome

---

Real example:

Lighthouse mobile score: 100/100 “Page is mobile-friendly”

Scan real device testing found:

Issue: Hero section cut off on iOS Safari

/* Your CSS */
.hero {
  height: 100vh; /* Works in Chrome, breaks in iOS Safari */
}

Why this breaks on iOS:

• iOS Safari’s bottom nav bar overlaps content
• 100vh doesn’t account for Safari’s dynamic UI (address bar shrinks/grows on scroll)
• Hero CTA button was hidden below the fold

Lighthouse simulation didn’t catch this because it uses Chrome’s mobile simulator, not real iOS Safari.

Impact:

• 40% of mobile visitors use iOS Safari (typical analytics split)
• Product Hunt traffic is 60% mobile
• Expected 3,000 mobile visitors → 1,200 saw broken hero with hidden CTA
• Estimated 30-50% conversion loss on iOS

Scan fix:

.hero {
  min-height: 100vh;
  min-height: -webkit-fill-available; /* iOS Safari fix */
}

---

4. Social Sharing Preview Validation

What Lighthouse checks: Whether Open Graph tags exist in HTML

What Scan checks: Whether tags exist AND whether images/previews actually work

---

Real example:

Your HTML (passes Lighthouse):

<meta property="og:image" content="https://example.com/og-image.png" />
<meta property="og:title" content="Product Name" />
<meta property="og:description" content="Product description" />

Lighthouse: “Open Graph tags found”

What Lighthouse missed:

1. og:image URL returns 404 (image file missing from build)
2. Missing Twitter Card tags (LinkedIn/Twitter won’t show preview)
3. Image dimensions wrong (1200×630 required for LinkedIn, you have 800×400)
4. Missing og:url tag (Twitter shows wrong URL in preview)

Scan catches:

og:image returns 404
   Impact: Broken image icon in social shares (Facebook, LinkedIn, Twitter)
   Fix: Add og-image.png to /public folder

Missing twitter:card tags
   Impact: No Twitter preview card
   Fix: Add twitter:card, twitter:title, twitter:image

og:image dimensions 800×400 (LinkedIn requires 1200×630)
   Impact: Image cropped awkwardly in LinkedIn previews
   Fix: Resize image to 1200×630

Missing og:url tag
   Impact: Twitter may show wrong canonical URL
   Fix: Add <meta property="og:url" content="https://example.com" />

Impact if you’d launched with broken social previews:

• Product Hunt listing shows broken image icon (unprofessional)
• Twitter shares get 50-70% fewer clicks without image preview
• LinkedIn shares use fallback tiny logo instead of hero image

---

5. Site-Wide Crawling (Lighthouse Only Audits One Page)

What Lighthouse checks: Single page you specify

What Scan checks: Full site crawl to find cross-page issues

---

Lighthouse limitation: You run Lighthouse on your homepage. It says “All good!”

What Lighthouse missed (because it only checked homepage):

1. 3 broken internal links on blog pages (404 errors)
2. 4 orphaned pages (no internal links pointing to them, not in sitemap)
3. Redirect chain (old blog URL → redirect → redirect → final page = 3 hops, wastes crawl budget)
4. Duplicate meta descriptions across 7 product pages (copy-pasted, hurts SEO)
5. Sitemap contains 5 URLs that 404 (Google crawls these, wastes crawl budget)

Scan crawl catches:

3 broken internal links
   /blog/post-old-url → 404 (update to /blog/post-new-url)

4 orphaned pages (no internal links)
   /docs/advanced-guide (not linked from anywhere, not in sitemap)
   Impact: Google won't discover these pages
   Fix: Add internal links from related docs

Redirect chain: /old-post → /newer-post → /final-post (3 hops)
   Impact: Wastes crawl budget, slow page load
   Fix: Update link directly to /final-post

7 pages with duplicate meta description
   Impact: Dilutes topical authority, confuses Google about page relevance
   Fix: Write unique descriptions for each page

Sitemap contains 5 URLs that return 404
   Impact: Google wastes crawl budget on broken pages
   Fix: Remove outdated URLs from sitemap

Impact:

• Broken links hurt trust and SEO authority
• Orphaned pages won’t rank (Google can’t discover them)
• Redirect chains slow site and waste crawl budget
• Duplicate meta descriptions dilute SEO relevance

---

Side-by-Side Comparison: Lighthouse vs Scan

What’s Checked	Lighthouse	Scan
Performance (LCP, FID, CLS)	Best-in-class	(via Lighthouse integration)
Core Web Vitals
Basic accessibility (about 50 checks)
Advanced accessibility (150+ WCAG checks)		(via pa11y)
Schema syntax validation
Schema optimization (missing types, incomplete fields)
Social sharing validation (OG tags exist)
Social preview testing (images load, dimensions correct)
Mobile simulator
Real device testing (iOS Safari, Android Chrome)
Single-page audit
Site-wide crawl (broken links, orphaned pages)
Meta tag strategy (duplicates, optimal length)	(only checks if exists)
Sitemap validation
Redirect chain detection

---

Real Case Study: Perfect Lighthouse, Broken Site

Client: SaaS marketing site redesign

Lighthouse audit results: 100/100 across all categories

• Performance: 100
• Accessibility: 100
• Best Practices: 100
• SEO: 100

Client’s conclusion: “We’re ready to launch!”

Scan audit results (48 hours before launch): 7 critical issues

1. Broken social previews (SHOWSTOPPER)

   • og:image 404ing
   • Would have launched with broken Product Hunt preview

2. Missing schema markup (HIGH PRIORITY)

   • Zero LocalBusiness or BreadcrumbList schema
   • Competitors had rich snippets, client didn’t

3. Mobile viewport bug on iOS Safari (SHOWSTOPPER)

   • Hero CTA hidden on 40% of mobile traffic
   • Lighthouse mobile simulator didn’t catch it

4. 404 errors in sitemap (MEDIUM PRIORITY)

   • 3 URLs in sitemap returned 404
   • Would have wasted Google’s crawl budget

5. Accessibility failures (HIGH PRIORITY)

   • 11 WCAG violations Lighthouse’s 50 checks missed
   • Screen reader users couldn’t complete signup form

6. Missing favicon (LOW PRIORITY)

   • Looked amateur (generic browser icon in tabs)

7. Performance regression (MEDIUM PRIORITY)

   • Unoptimized images (2.4 MB hero image)
   • Lighthouse caught this, but didn’t flag as critical

Impact if they’d launched without Scan:

• Broken social previews → 40% fewer Product Hunt clicks
• iOS Safari bug → 30% conversion loss on mobile
• Accessibility issues → 5-10% conversion loss
• Estimated total loss: $91K in first-year ARR

Cost to fix: 2 hours team time + $50 Site Audit

ROI: $50 → prevented $91K loss = 1,820x return

---

Why Lighthouse Doesn’t Check These Things

Lighthouse’s purpose: Optimize web performance and catch obvious technical issues

Lighthouse is NOT designed for:

• SEO strategy with 30+ checks (schema optimization, meta tag strategy, duplicate content)
• Advanced accessibility (only about 50 of 150+ WCAG rules)
• Real device testing (uses simulators)
• Site-wide analysis (audits one page at a time)

Lighthouse is a performance tool, not an SEO tool.

This isn’t a criticism of Lighthouse. It’s just not designed for pre-launch audits covering 150+ checks across 5 categories.

---

When to Use Lighthouse vs Scan

Use Lighthouse For:

• Performance optimization (LCP, FID, CLS)
• Core Web Vitals monitoring
• Quick page speed checks during development
• Progressive Web App (PWA) validation

Use Scan For:

• Pre-launch audits (catch issues before users see them)
• Schema markup optimization (not just validation)
• Advanced accessibility (WCAG 2.1 AA compliance)
• Real device testing (iOS Safari, Android Chrome)
• Social sharing validation (images load, previews work)
• Site-wide crawling (broken links, orphaned pages)

Use Both:

• Lighthouse during development (fast performance checks)
• Scan before launch (pre-launch audit with 150+ checks)

---

The Complementary Workflow

Most teams use both:

During development (weekly):

• Run Lighthouse on each page as you build
• Fix performance issues (image optimization, render-blocking resources)
• Catch basic accessibility issues

Before launch (48 hours pre-launch):

• Run Scan on staging site
• Catch schema optimization gaps
• Test real devices (iOS Safari, Android Chrome)
• Validate social previews
• Crawl entire site for broken links
• Fix critical issues before launch

After launch (quarterly):

• Run Lighthouse for ongoing performance monitoring
• Run Scan to catch regressions (schema issues, new broken links, accessibility problems)

---

Pricing Comparison

Lighthouse: Free (built into Chrome DevTools)

Scan: $50 per audit

Why pay for Scan when Lighthouse is free?

Scan catches issues Lighthouse doesn’t (schema optimization, advanced accessibility, real device bugs, social previews, site-wide crawling)

ROI example:

• Scan audit: $50
• Caught broken social preview before Product Hunt launch
• Prevented 40% CTR loss = ~$50K ARR saved
• ROI: 2,000x

Most teams: Use free Lighthouse during development, pay $50 for Scan before major launches

---

The Bottom Line

Lighthouse is excellent for what it’s designed to do: performance optimization and basic technical checks.

Lighthouse is NOT comprehensive for SEO, accessibility, or pre-launch audits.

Scan catches:

• Schema optimization (not just validation)
• Advanced accessibility (150+ checks vs Lighthouse’s 50)
• Real device bugs (iOS Safari, Android Chrome)
• Social sharing validation (images load, previews work)
• Site-wide issues (broken links, orphaned pages, redirect chains)

One $50 Site Audit before launch can prevent $50K-100K in lost revenue from conversion killers Lighthouse doesn’t check.

Your Lighthouse score might be perfect. Your site probably isn’t.

---

Related Reading

• Your Lighthouse Score is a Lie: 5 Critical Errors It Missed
• The 15-Minute Pre-Launch Website QA That Saved Our Product Launch
• Scan vs Free Tools (Lighthouse, GTmetrix, WebPageTest)
• Is Scan a Replacement for Semrush or Ahrefs?

Ready to catch what Lighthouse missed? Try Site Audit or run a Scan audit ($50) and get prioritized fix list before launch. Perfect Lighthouse scores don’t guarantee launch success. | Log in