Web quality audit

Comprehensive quality review based on Google Lighthouse audits. Covers Performance, Accessibility, SEO, and Best Practices across 150+ checks.

Lighthouse v13 note (Oct 2025+). Lighthouse has migrated the Performance category from per-opportunity audits to Performance Insight Audits (announcement). Several individual audit names this skill historically referenced — First Meaningful Paint, No Document Write, Uses Passive Event Listeners, Uses Rel Preload — have been removed or merged. The underlying advice is unchanged and still applies; only the report format moved. The CLS-related audits ("layout shifts", "non-composited animations", "unsized images") are now consolidated into a single cls-culprits-insight, and image audits are merged into image-delivery-insight. Treat older Lighthouse JSON output as a superset, not a contradiction.

How it works

1. Analyze the provided code/project for quality issues
2. Categorize findings by severity (Critical, High, Medium, Low)
3. Provide specific, actionable recommendations
4. Include code examples for fixes

Audit categories

Performance (40% of typical issues)

Core Web Vitals — Must pass for good page experience:

• LCP (Largest Contentful Paint) < 2.5s. The largest visible element must render quickly. Optimize images, fonts, and server response time.
• INP (Interaction to Next Paint) < 200ms. User interactions must feel instant. Reduce JavaScript execution time and break up long tasks.
• CLS (Cumulative Layout Shift) < 0.1. Content must not jump around. Set explicit dimensions on images, embeds, and ads.

Resource Optimization:

• Compress images. Use WebP/AVIF with fallbacks. Serve correctly sized images via srcset.
• Minimize JavaScript. Remove unused code. Use code splitting. Defer non-critical scripts.
• Optimize CSS. Extract critical CSS. Remove unused styles. Avoid @import.
• Efficient fonts. Use font-display: swap. Preload critical fonts. Subset to needed characters.

Loading Strategy:

• Preconnect to origins. Add <link rel="preconnect"> for third-party domains.
• Preload critical assets. LCP images, fonts, and above-fold CSS.
• Lazy load below-fold content. Images, iframes, and heavy components.
• Cache effectively. Long cache TTLs for static assets. Immutable caching for hashed files.

Accessibility (30% of typical issues)

Perceivable:

• Text alternatives. Every <img> has meaningful alt text. Decorative images use alt="".
• Color contrast. Minimum 4.5:1 for normal text, 3:1 for large text (WCAG AA).
• Don't rely on color alone. Use icons, patterns, or text alongside color indicators.
• Captions and transcripts. Video has captions. Audio has transcripts.

Operable:

• Keyboard accessible. All functionality available via keyboard. No keyboard traps.
• Focus visible. Clear focus indicators on all interactive elements.
• Skip links. Provide "Skip to main content" for keyboard users.
• Sufficient time. Users can extend time limits. No auto-advancing content without controls.

Understandable:

• Page language. Set lang attribute on <html>.
• Consistent navigation. Same navigation structure across pages.
• Error identification. Form errors clearly described and associated with fields.
• Labels and instructions. All form inputs have associated labels.

Robust:

• Valid HTML. No duplicate IDs. Properly nested elements.
• ARIA used correctly. Prefer native elements. ARIA roles match behavior.
• Name, role, value. Interactive elements have accessible names and correct roles.

SEO (15% of typical issues)

Crawlability:

• Valid robots.txt. Doesn't block important resources.
• XML sitemap. Lists all important pages. Submitted to Search Console.
• Canonical URLs. Prevent duplicate content issues.
• No noindex on important pages. Check meta robots and headers.

On-Page SEO:

• Unique title tags. 50-60 characters. Primary keyword included.
• Meta descriptions. 150-160 characters. Compelling and unique.
• Heading hierarchy. Single <h1>. Logical heading structure.
• Descriptive link text. Not "click here" or "read more".

Technical SEO:

• Mobile-friendly. Responsive design. Tap targets ≥ 48px.
• HTTPS. Secure connection required.
• Fast loading. Performance directly impacts ranking.
• Structured data. JSON-LD for rich snippets (Article, Product, FAQ, etc.).

Best practices (15% of typical issues)

Security:

• HTTPS everywhere. No mixed content. HSTS enabled.
• No vulnerable libraries. Keep dependencies updated.
• CSP headers. Content Security Policy to prevent XSS.
• No exposed source maps. In production builds.

Modern Standards:

• No deprecated APIs. Replace document.write, synchronous XHR, etc.
• Valid doctype. Use <!DOCTYPE html>.
• Charset declared. <meta charset="UTF-8"> as first element in <head>.
• No browser errors. Clean console. No CORS issues.

UX Patterns:

• No intrusive interstitials. Especially on mobile.
• Clear permission requests. Only ask when needed, with context.
• No misleading buttons. Buttons do what they say.

Severity levels

Audit output format

When performing an audit, structure findings as:

## Audit results

### Critical issues (X found)
- **[Category]** Issue description. File: `path/to/file.js:123`
  - **Impact:** Why this matters
  - **Fix:** Specific code change or recommendation

### High priority (X found)
...

### Summary
- Performance: X issues (Y critical)
- Accessibility: X issues (Y critical)
- SEO: X issues
- Best Practices: X issues

### Recommended priority
1. First fix this because...
2. Then address...
3. Finally optimize...

Quick checklist

Before every deploy

• Core Web Vitals passing
• No accessibility errors (axe/Lighthouse)
• No console errors
• HTTPS working
• Meta tags present

Weekly review

• Check Search Console for issues
• Review Core Web Vitals trends
• Update dependencies
• Test with screen reader

Monthly deep dive

• Full Lighthouse audit
• Performance profiling
• Accessibility audit with real users
• SEO keyword review

References

For detailed guidelines on specific areas:

• Performance Optimization
• Core Web Vitals
• Accessibility
• SEO
• Best Practices