SEO optimisation

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

SEO fundamentals

Search ranking factors (approximate influence)

Factor	Influence	This Skill
Content quality & relevance	~40%	Partial (structure)
Backlinks & authority	~25%	No
Technical SEO	~15%	Yes
Page experience (Core Web Vitals)	~10%	See Core Web Vitals
On-page SEO	~10%	Yes

Technical SEO

Crawlability

robots.txt:

code

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

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

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

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

Meta robots:

html

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

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

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

Canonical URLs:

html

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

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

XML sitemap

xml

<?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>
    <priority>1.0</priority>
  </url>
  <url>
    <loc>https://example.com/products</loc>
    <lastmod>2024-01-14</lastmod>
    <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 only when content genuinely changes. Submit to Google Search Console. Note: changefreq is ignored by Google and can be omitted.

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

html

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

Security headers for SEO trust signals:

code

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

On-page SEO

Title tags

html

<!-- Bad: missing or generic -->
<title>Page</title>
<title>Home</title>

<!-- Good: 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

html

<!-- Bad: missing or duplicate -->
<meta name="description" content="">

<!-- Good: 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

html

<!-- Bad: poor structure -->
<h2>Welcome to Our Store</h2>
<h4>Products</h4>
<h1>Contact Us</h1>

<!-- Good: 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

html

<!-- Bad: poor image SEO -->
<img src="IMG_12345.jpg">

<!-- Good: optimised 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

html

<!-- Bad: non-descriptive -->
<a href="/products">Click here</a>
<a href="/widgets">Read more</a>

<!-- Good: 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)

WebSite (sitelinks search box)

html

<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "WebSite",
  "name": "Example Site",
  "url": "https://example.com",
  "potentialAction": {
    "@type": "SearchAction",
    "target": "https://example.com/search?q={search_term_string}",
    "query-input": "required name=search_term_string"
  }
}
</script>

Organization

html

<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

html

<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

html

<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

html

<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "FAQPage",
  "mainEntity": [
    {
      "@type": "Question",
      "name": "What colours 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

html

<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: Google Rich Results Test, Schema.org Validator

Mobile SEO

Responsive design

html

<!-- Bad: not mobile-friendly -->
<meta name="viewport" content="width=1024">

<!-- Good: responsive viewport -->
<meta name="viewport" content="width=device-width, initial-scale=1">

Tap targets

css

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

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

Font sizes

css

/* Bad: too small on mobile */
body { font-size: 10px; }

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

International SEO

Hreflang tags

html

<!-- 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

<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