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seo-technical-audit

Expert guide for technical SEO auditing. Use when checking crawlability, indexing issues, page speed, Core Web Vitals, mobile-friendliness, HTTPS configuration, robots.txt, XML sitemaps, canonical tags, hreflang, redirect chains, HTTP status codes, or diagnosing technical SEO problems.

personAuthor: jakexiaohubgithub
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Technical SEO Audit

Crawlability

Search engines must be able to discover and access your pages. Crawlability issues block indexing entirely.

Robots.txt

Controls which URLs crawlers can access.

# Allow all crawlers access to everything
User-agent: *
Allow: /

# Block specific paths
User-agent: *
Disallow: /admin/
Disallow: /api/
Disallow: /staging/
Disallow: /*?sort=
Disallow: /*?filter=

# Sitemap reference (always include)
Sitemap: https://example.com/sitemap.xml

Critical rules:

  • Never block CSS/JS files (Google needs them to render pages)
  • Never block important content paths accidentally
  • Test with analyze_robots_txt before deploying changes
  • Crawl-delay is ignored by Google (honored by Bing/Yandex)

Meta Robots & X-Robots-Tag

Page-level crawl and index directives.

| Directive | Effect | |-----------|--------| | index | Allow indexing (default) | | noindex | Prevent indexing — removes from search results | | follow | Follow links on this page (default) | | nofollow | Don't follow any links on this page | | noarchive | Don't show cached version | | nosnippet | Don't show text snippet in results | | max-snippet:N | Limit snippet to N characters | | max-image-preview:large | Allow large image previews |

<!-- In HTML head -->
<meta name="robots" content="noindex, follow">

<!-- Via HTTP header (for non-HTML files) -->
X-Robots-Tag: noindex, nofollow

MCP Tool: analyze_page extracts both meta robots and HTTP header directives.

Indexing

Canonical Tags

The definitive way to tell search engines which URL is the preferred version.

Rules:

  • Every indexable page: self-referencing canonical
  • Absolute URLs only (https://example.com/page, not /page)
  • Must be consistent: canonical URL must return 200 (not redirect or 404)
  • One canonical per page (if multiple, Google uses the first)
  • HTTP header canonical overrides HTML canonical if both present

Noindex vs Canonical

| Scenario | Use | |----------|-----| | Page should never appear in search | noindex | | Duplicate page, prefer another version | canonical to preferred version | | URL parameter variants | canonical to clean URL | | Paginated content | Self-referencing canonical on each page |

Sitemap Submission

  • Submit via Google Search Console
  • All indexable pages should be in the sitemap
  • Noindex pages should NOT be in the sitemap
  • Keep sitemaps under 50,000 URLs / 50MB per file (use sitemap index for larger sites)

MCP Tools: analyze_sitemap validates structure, gsc_sitemaps checks submission status.

Core Web Vitals

Google's page experience signals. Measured from real user data (CrUX) and lab data (Lighthouse).

Thresholds (2024+)

| Metric | Good | Needs Improvement | Poor | |--------|------|-------------------|------| | LCP (Largest Contentful Paint) | ≤ 2.5s | ≤ 4.0s | > 4.0s | | INP (Interaction to Next Paint) | ≤ 200ms | ≤ 500ms | > 500ms | | CLS (Cumulative Layout Shift) | ≤ 0.1 | ≤ 0.25 | > 0.25 |

LCP Optimization

Largest Contentful Paint measures when the largest visible element finishes rendering.

Common causes of poor LCP:

  1. Slow server response (TTFB > 800ms) → optimize server, use CDN
  2. Render-blocking resources → defer non-critical CSS/JS
  3. Slow resource load → optimize/compress LCP image, use preload
  4. Client-side rendering → server-side render critical content

Quick wins:

  • Preload LCP image: <link rel="preload" href="hero.webp" as="image">
  • Use CDN for static assets
  • Optimize server response (caching, database queries)
  • Avoid lazy-loading the LCP element

INP Optimization

Interaction to Next Paint measures responsiveness to user input.

Common causes of poor INP:

  1. Long JavaScript tasks blocking main thread → break into smaller tasks
  2. Heavy event handlers → debounce, use requestAnimationFrame
  3. Large DOM size → reduce DOM nodes (target < 1,500)
  4. Third-party scripts → defer or lazy-load

CLS Optimization

Cumulative Layout Shift measures visual stability.

Common causes of poor CLS:

  1. Images without dimensions → always set width and height
  2. Ads/embeds without reserved space → use aspect-ratio or min-height
  3. Web fonts causing FOIT/FOUT → use font-display: swap + preload
  4. Dynamically injected content → reserve space before injection

MCP Tool: check_core_web_vitals returns all metrics with specific optimization suggestions.

Page Speed Optimization

Beyond Core Web Vitals, overall page speed impacts user experience and crawl budget.

Critical rendering path

  1. Minimize render-blocking resources (critical CSS inline, defer JS)
  2. Enable compression (Brotli preferred, gzip minimum)
  3. Set cache headers (Cache-Control: max-age=31536000 for static assets)
  4. Use HTTP/2 or HTTP/3
  5. Minimize main-thread work (reduce JS execution time)

Image optimization

  • Use modern formats (WebP/AVIF)
  • Serve responsive images (srcset)
  • Lazy load below-the-fold images
  • Compress aggressively (80-85% quality)

Resource hints

<link rel="preconnect" href="https://fonts.googleapis.com">
<link rel="preload" href="/critical.css" as="style">
<link rel="prefetch" href="/next-page.html">
<link rel="dns-prefetch" href="https://analytics.example.com">

Mobile-Friendliness

Google uses mobile-first indexing — the mobile version of your site is what gets indexed.

Requirements

  • Viewport meta tag: <meta name="viewport" content="width=device-width, initial-scale=1">
  • Responsive design (content adapts to screen size)
  • No horizontal scrolling
  • Tap targets: minimum 48x48px with 8px spacing
  • Font size: minimum 16px for body text
  • No intrusive interstitials (popups covering content)
  • Content parity: mobile version has same content as desktop

MCP Tool: check_mobile_friendly evaluates all mobile usability factors.

HTTPS & Security

HTTPS requirements

  • All pages served over HTTPS (no HTTP pages in index)
  • Valid SSL certificate (not expired, correct domain)
  • No mixed content (HTTPS page loading HTTP resources)
  • HSTS header recommended: Strict-Transport-Security: max-age=31536000; includeSubDomains
  • HTTP pages 301 redirect to HTTPS

Common HTTPS issues

| Issue | Impact | Fix | |-------|--------|-----| | Mixed content | Medium | Update all resource URLs to HTTPS | | Expired certificate | Critical | Renew SSL certificate immediately | | HTTP pages indexed | High | 301 redirect HTTP → HTTPS + update canonical | | Missing HSTS | Low | Add HSTS header |

Redirects

Redirect types

| Code | Type | When to Use | SEO Impact | |------|------|-------------|------------| | 301 | Permanent | URL changed permanently, content moved | Passes ~95% link equity | | 302 | Temporary | Temporary move (A/B test, maintenance) | Does not pass link equity | | 307 | Temporary (strict) | Same as 302 but preserves HTTP method | Does not pass link equity | | 308 | Permanent (strict) | Same as 301 but preserves HTTP method | Passes link equity |

Redirect issues

  • Redirect chains: A → B → C → D. Maximum 2 hops recommended. Fix by pointing A directly to D.
  • Redirect loops: A → B → A. Critical error — page becomes inaccessible.
  • Soft 404s: Page returns 200 but shows "not found" content. Should return actual 404.
  • 302 where 301 needed: Temporary redirect for permanent move wastes link equity.

XML Sitemaps

Requirements

  • Located at /sitemap.xml (or referenced in robots.txt)
  • Valid XML format
  • Only indexable pages (no noindex, no 404s, no redirects)
  • Include <lastmod> with accurate dates (ISO 8601)
  • Maximum 50,000 URLs per sitemap file
  • Maximum 50MB uncompressed per file
  • Use sitemap index for larger sites

Validation

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <url>
    <loc>https://example.com/page</loc>
    <lastmod>2026-01-15</lastmod>
    <changefreq>weekly</changefreq>
    <priority>0.8</priority>
  </url>
</urlset>

MCP Tool: analyze_sitemap parses, validates, and reports issues.

Hreflang (International SEO)

For multi-language or multi-region sites. Tells Google which language/region version to show.

Syntax

<link rel="alternate" hreflang="en-us" href="https://example.com/page">
<link rel="alternate" hreflang="en-gb" href="https://example.co.uk/page">
<link rel="alternate" hreflang="es" href="https://example.com/es/page">
<link rel="alternate" hreflang="x-default" href="https://example.com/page">

Rules

  • Bidirectional: If page A references page B, page B must reference page A
  • Self-referencing: Each page must include a hreflang pointing to itself
  • x-default: Include for the fallback/language selector page
  • Return tags: Every referenced URL must return the same hreflang set
  • Use ISO 639-1 language codes, optionally with ISO 3166-1 region codes

HTTP Status Codes (SEO Impact)

| Code | Meaning | SEO Action | |------|---------|------------| | 200 | OK | Expected for all indexable pages | | 301 | Moved Permanently | Passes link equity. Use for permanent URL changes | | 302 | Found (Temporary) | Does NOT pass link equity. Use only for temporary moves | | 304 | Not Modified | Good — efficient caching | | 404 | Not Found | Remove from sitemap, fix internal links pointing here | | 410 | Gone | Permanently removed. Stronger signal than 404 for deindexing | | 500 | Server Error | Fix immediately — blocks crawling and indexing | | 503 | Service Unavailable | Temporary. Google retries. Use for planned maintenance |

Technical Audit Workflow

Recommended order for a complete technical audit:

  1. Crawlability: analyze_robots_txt → check for blocking issues
  2. Sitemap: analyze_sitemap → validate structure and URLs
  3. Page-level: analyze_page → meta robots, canonical, redirects, status
  4. Performance: check_core_web_vitals → LCP, INP, CLS scores
  5. Mobile: check_mobile_friendly → viewport, tap targets, fonts
  6. Schema: extract_schema → structured data validation
  7. GSC data: gsc_index_coverage → real indexing status from Google

See ERROR_CATALOG.md for the complete issue catalog. See AUDIT_WORKFLOW.md for detailed audit methodology. See HTTP_STATUS_REFERENCE.md for complete status code reference.