---
name: seo
description: "สกิลสำหรับSEO ใช้เมื่อต้องการคำแนะนำ ขั้นตอนปฏิบัติ แพตเทิร์น หรือแนวทางแก้ปัญหาที่เกี่ยวข้องกับหัวข้อนี้"
license: MIT
metadata:
  author: web-quality-skills
  version: "1.0"
---

# 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">
{
  "@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 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

```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

Test structured data at:
- [Google Rich Results Test](https://search.google.com/test/rich-results)
- [Schema.org Validator](https://validator.schema.org/)

---

## Mobile SEO

### Responsive design

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

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

### Tap targets

```css
/* ❌ 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

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

/* ✅ 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](https://developers.google.com/search)
- [Schema.org](https://schema.org/)
- [Core Web Vitals](../core-web-vitals/SKILL.md)
- [Web Quality Audit](../web-quality-audit/SKILL.md)
