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:**

```text
# /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:**

```html
<!-- 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:**

```html
<!-- 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
<?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

```html
<!-- 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

```html
<!-- ❌ 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

```html
<!-- ❌ 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

```html
<!-- ❌ 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

```html
<!-- ❌ 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

```html
<!-- ❌ 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

```html
<script type="application/ld+json">
  {