seo

SEO optimization

Search engine optimization based on Lighthouse SEO audits and Google Search guidelines. Focus on technical SEO, on-page optimization, and structured data.

SEO fundamentals

Search ranking factors (approximate influence):

| Factor | Influence | This Skill | |--------|-----------|------------| | Content quality & relevance | ~40% | Partial (structure) | | Backlinks & authority | ~25% | ✗ | | Technical SEO | ~15% | ✓ | | Page experience (Core Web Vitals) | ~10% | See [Core Web Vitals](../core-web-vitals/SKILL.md) | | On-page SEO | ~10% | ✓ |

Technical SEO

Crawlability

robots.txt:

# /robots.txt
User-agent: *
Allow: /

# Block admin/private areas
Disallow: /admin/
Disallow: /api/
Disallow: /private/

# Don't block resources needed for rendering
# ❌ Disallow: /static/

Sitemap: https://example.com/sitemap.xml

Meta robots:

<!-- Default: indexable, followable -->
<meta name="robots" content="index, follow">

<!-- Noindex specific pages -->
<meta name="robots" content="noindex, nofollow">

<!-- Indexable but don't follow links -->
<meta name="robots" content="index, nofollow">

<!-- Control snippets -->
<meta name="robots" content="max-snippet:150, max-image-preview:large">

Canonical URLs:

<!-- Prevent duplicate content issues -->
<link rel="canonical" href="https://example.com/page">

<!-- Self-referencing canonical (recommended) -->
<link rel="canonical" href="https://example.com/current-page">

<!-- For paginated content -->
<link rel="canonical" href="https://example.com/products">
<!-- Or use rel="prev" / rel="next" for explicit pagination -->

XML sitemap

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <url>
    <loc>https://example.com/</loc>
    <lastmod>2024-01-15</lastmod>
    <changefreq>daily</changefreq>
    <priority>1.0</priority>
  </url>
  <url>
    <loc>https://example.com/products</loc>
    <lastmod>2024-01-14</lastmod>
    <changefreq>weekly</changefreq>
    <priority>0.8</priority>
  </url>
</urlset>

Sitemap best practices:

• Maximum 50,000 URLs or 50MB per sitemap
• Use sitemap index for larger sites
• Include only canonical, indexable URLs
• Update lastmod when content changes
• Submit to Google Search Console

URL structure

✅ Good URLs:
https://example.com/products/blue-widget
https://example.com/blog/how-to-use-widgets

❌ Poor URLs:
https://example.com/p?id=12345
https://example.com/products/item/category/subcategory/blue-widget-2024-sale-discount

URL guidelines:

• Use hyphens, not underscores
• Lowercase only
• Keep short (< 75 characters)
• Include target keywords naturally
• Avoid parameters when possible
• Use HTTPS always

HTTPS & security

<!-- Ensure all resources use HTTPS -->
<img src="https://example.com/image.jpg">

<!-- Not: -->
<img src="http://example.com/image.jpg">

Security headers for SEO trust signals:

Strict-Transport-Security: max-age=31536000; includeSubDomains
X-Content-Type-Options: nosniff
X-Frame-Options: DENY

On-page SEO

Title tags

<!-- ❌ Missing or generic -->
<title>Page</title>
<title>Home</title>

<!-- ✅ Descriptive with primary keyword -->
<title>Blue Widgets for Sale | Premium Quality | Example Store</title>

Title tag guidelines:

• 50-60 characters (Google truncates ~60)
• Primary keyword near the beginning
• Unique for every page
• Brand name at end (unless homepage)
• Action-oriented when appropriate

Meta descriptions

<!-- ❌ Missing or duplicate -->
<meta name="description" content="">

<!-- ✅ Compelling and unique -->
<meta name="description" content="Shop premium blue widgets with free shipping. 30-day returns. Rated 4.9/5 by 10,000+ customers. Order today and save 20%.">

Meta description guidelines:

• 150-160 characters
• Include primary keyword naturally
• Compelling call-to-action
• Unique for every page
• Matches page content

Heading structure

<!-- ❌ Poor structure -->
<h2>Welcome to Our Store</h2>
<h4>Products</h4>
<h1>Contact Us</h1>

<!-- ✅ Proper hierarchy -->
<h1>Blue Widgets - Premium Quality</h1>
  <h2>Product Features</h2>
    <h3>Durability</h3>
    <h3>Design</h3>
  <h2>Customer Reviews</h2>
  <h2>Pricing</h2>

Heading guidelines:

• Single <h1> per page (the main topic)
• Logical hierarchy (don't skip levels)
• Include keywords naturally
• Descriptive, not generic

Image SEO

<!-- ❌ Poor image SEO -->
<img src="IMG_12345.jpg">

<!-- ✅ Optimized image -->
<img src="blue-widget-product-photo.webp"
     alt="Blue widget with chrome finish, side view showing control panel"
     width="800"
     height="600"
     loading="lazy">

Image guidelines:

• Descriptive filenames with keywords
• Alt text describes the image content
• Compressed and properly sized
• WebP/AVIF with fallbacks
• Lazy load below-fold images

Internal linking

<!-- ❌ Non-descriptive -->
<a href="/products">Click here</a>
<a href="/widgets">Read more</a>

<!-- ✅ Descriptive anchor text -->
<a href="/products/blue-widgets">Browse our blue widget collection</a>
<a href="/guides/widget-maintenance">Learn how to maintain your widgets</a>

Linking guidelines:

• Descriptive anchor text with keywords
• Link to relevant internal pages
• Reasonable number of links per page
• Fix broken links promptly
• Use breadcrumbs for hierarchy

Structured data (JSON-LD)

Organization

<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "Organization",
  "name": "Example Company",
  "url": "https://example.com",
  "logo": "https://example.com/logo.png",
  "sameAs": [
    "https://twitter.com/example",
    "https://linkedin.com/company/example"
  ],
  "contactPoint": {
    "@type": "ContactPoint",
    "telephone": "+1-555-123-4567",
    "contactType": "customer service"
  }
}
</script>

Article

<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "Article",
  "headline": "How to Choose the Right Widget",
  "description": "Complete guide to selecting widgets for your needs.",
  "image": "https://example.com/article-image.jpg",
  "author": {
    "@type": "Person",
    "name": "Jane Smith",
    "url": "https://example.com/authors/jane-smith"
  },
  "publisher": {
    "@type": "Organization",
    "name": "Example Blog",
    "logo": {
      "@type": "ImageObject",
      "url": "https://example.com/logo.png"
    }
  },
  "datePublished": "2024-01-15",
  "dateModified": "2024-01-20"
}
</script>

Product

<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": "Blue Widget Pro",
  "image": "https://example.com/blue-widget.jpg",
  "description": "Premium blue widget with advanced features.",
  "brand": {
    "@type": "Brand",
    "name": "WidgetCo"
  },
  "offers": {
    "@type": "Offer",
    "price": "49.99",
    "priceCurrency": "USD",
    "availability": "https://schema.org/InStock",
    "url": "https://example.com/products/blue-widget"
  },
  "aggregateRating": {
    "@type": "AggregateRating",
    "ratingValue": "4.8",
    "reviewCount": "1250"
  }
}
</script>

FAQ

<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "FAQPage",
  "mainEntity": [
    {
      "@type": "Question",
      "name": "What colors are available?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Our widgets come in blue, red, and green."
      }
    },
    {
      "@type": "Question",
      "name": "What is the warranty?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "All widgets include a 2-year warranty."
      }
    }
  ]
}
</script>

Breadcrumbs

<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "BreadcrumbList",
  "itemListElement": [
    {
      "@type": "ListItem",
      "position": 1,
      "name": "Home",
      "item": "https://example.com"
    },
    {
      "@type": "ListItem",
      "position": 2,
      "name": "Products",
      "item": "https://example.com/products"
    },
    {
      "@type": "ListItem",
      "position": 3,
      "name": "Blue Widgets",
      "item": "https://example.com/products/blue-widgets"
    }
  ]
}
</script>

Validation

Test structured data at:

• Google Rich Results Test
• Schema.org Validator

AI search visibility (emerging)

A class of AI search engines (ChatGPT search, Perplexity, Gemini Overviews) cite web pages from their training and retrieval pipelines, not from the classic ranked results. As of 2026 this is an unstable area — there are no confirmed ranking signals — but a few things are low-cost and won't hurt:

• Don't block AI crawlers wholesale. OAI-SearchBot, PerplexityBot, GoogleOther, Google-Extended, ClaudeBot, etc. each have separate robots.txt user-agents. Decide per-bot rather than blanket-blocking — a Disallow removes you from that bot's citations.
• Lean on schema.org Article/Product/FAQPage. AI summarizers parse structured data more reliably than they parse prose layouts. The structured-data examples above are the same ones that help here.
• Make first-paragraph answers self-contained. Both featured snippets and AI summaries pull short, coherent passages. A definition or direct answer in the first 1-2 sentences is more extractable than the same content buried under marketing prose.

llms.txt — emerging, unproven

llms.txt is a proposed convention (a Markdown index of your site's important pages, served at /llms.txt) for LLMs to consume. As of mid-2026 adoption is ~0.015% of sites and no major AI vendor has confirmed they read it. Treat it as a 5-minute speculative add for content sites — not a meaningful ranking or citation factor — and don't reorganize content around it.

Mobile SEO

Responsive design

<!-- ❌ Not mobile-friendly -->
<meta name="viewport" content="width=1024">

<!-- ✅ Responsive viewport -->
<meta name="viewport" content="width=device-width, initial-scale=1">

Tap targets

/* ❌ Too small for mobile */
.small-link {
  padding: 4px;
  font-size: 12px;
}

/* ✅ Adequate tap target */
.mobile-friendly-link {
  padding: 12px;
  font-size: 16px;
  min-height: 48px;
  min-width: 48px;
}

Font sizes

/* ❌ Too small on mobile */
body {
  font-size: 10px;
}

/* ✅ Readable without zooming */
body {
  font-size: 16px;
  line-height: 1.5;
}

International SEO

Hreflang tags

<!-- For multi-language sites -->
<link rel="alternate" hreflang="en" href="https://example.com/page">
<link rel="alternate" hreflang="es" href="https://example.com/es/page">
<link rel="alternate" hreflang="fr" href="https://example.com/fr/page">
<link rel="alternate" hreflang="x-default" href="https://example.com/page">

Language declaration

<html lang="en">
<!-- or -->
<html lang="es-MX">

SEO audit checklist

Critical

• [ ] HTTPS enabled
• [ ] robots.txt allows crawling
• [ ] No noindex on important pages
• [ ] Title tags present and unique
• [ ] Single <h1> per page

High priority

• [ ] Meta descriptions present
• [ ] Sitemap submitted
• [ ] Canonical URLs set
• [ ] Mobile-responsive
• [ ] Core Web Vitals passing

Medium priority

• [ ] Structured data implemented
• [ ] Internal linking strategy
• [ ] Image alt text
• [ ] Descriptive URLs
• [ ] Breadcrumb navigation

Ongoing

• [ ] Fix crawl errors in Search Console
• [ ] Update sitemap when content changes
• [ ] Monitor ranking changes
• [ ] Check for broken links
• [ ] Review Search Console insights

Tools

| Tool | Use | |------|-----| | Google Search Console | Monitor indexing, fix issues | | Google PageSpeed Insights | Performance + Core Web Vitals | | Rich Results Test | Validate structured data | | Lighthouse | Full SEO audit | | Screaming Frog | Crawl analysis |

References

• Google Search Central
• Schema.org
• [Core Web Vitals](../core-web-vitals/SKILL.md)
• [Web Quality Audit](../web-quality-audit/SKILL.md)