Technical SEO

Audit and fix the layer beneath the content: how search engines crawl, render, index, and trust a site. Stack-agnostic.

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When to use

• Site-wide audit before or after a migration
• Investigating indexing or ranking drops
• Setting up SEO foundations on a new site
• Auditing Core Web Vitals or page experience signals
• Fixing crawl waste, redirect chains, or canonical issues
• Setting up multilingual or multi-regional sites

When NOT to use

• Single-page on-page optimization (use seo-onpage)
• Keyword strategy or content planning (use seo-keyword)
• Competitor backlink or SERP analysis (use seo-competitor)
• Pure performance optimization without SEO context (use performance-optimization)

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Required inputs

• The site URL or staging URL
• Access to (at minimum) view the rendered HTML, robots.txt, and sitemap
• Ideally: search console access, server logs, and a crawler

If the site is large (10K+ URLs), confirm whether the audit is a full crawl or a sample.

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The framework: 6 layers

Technical SEO has six layers, stacked. A failure in a lower layer breaks everything above it.

1. Crawlability

Can search engines access the URLs?

• robots.txt does not block important paths
• No accidental noindex on indexable pages
• No accidental disallow patterns blocking CSS or JS (rendering breaks)
• Sitemap is present, returns 200, and lists canonical URLs only
• Sitemap is referenced in robots.txt
• No infinite spaces (faceted nav generating endless URLs)
• Crawl budget is not wasted on low-value URLs

2. Indexability

Of crawlable URLs, which should be indexed?

• One canonical URL per piece of content (no duplicates)
• Canonical tags self-reference on canonical pages
• noindex on staging, search results, filter pages, thank-you pages, internal admin
• No mixed signals (canonical pointing one way, sitemap another, internal links a third)
• Pagination handled correctly (rel=next/prev is deprecated, but consistent canonicals matter)
• Parameter handling deliberate (UTM, session IDs, sort orders)

3. Rendering

Does the rendered HTML match what crawlers see?

• Critical content visible without JavaScript (or properly server-rendered)
• For SPAs: confirm Googlebot sees the rendered content (test with the URL Inspection tool)
• No cloaking (showing different content to bots vs users)
• Lazy-loaded content has proper loading attributes
• Hydration errors do not strip content from the rendered DOM

4. Site architecture

Is the site structured for both users and crawlers?

• Clear URL hierarchy that mirrors site structure
• Important pages reachable in 3 clicks or fewer from the homepage
• Internal linking distributes authority logically
• Breadcrumb navigation present and marked up with schema
• No orphan pages (pages with no internal links)
• No redirect chains (one redirect max)
• No 4xx errors on internally-linked URLs

5. Structured data and signals

Does the site speak crawler language?

• Schema.org markup on appropriate page types
• JSON-LD format (preferred over microdata)
• Validates in the Rich Results Test
• Organization or LocalBusiness schema on the homepage or about page
• BreadcrumbList schema on nested pages
• Author and publisher schema linked correctly on content pages
• llms.txt present at the root (for AI crawlers, see seo-aeo-geo)

6. Page experience and security

Does the site meet the page experience baseline?

• HTTPS on all pages, no mixed content
• HSTS header set
• Core Web Vitals pass (LCP, INP, CLS within thresholds)
• Mobile-friendly (responsive, no horizontal scroll, tap targets sized correctly)
• No intrusive interstitials on mobile
• Stable URL structure (no random URL changes between deploys)
• 404 pages return 404, not 200 with "page not found" content (soft 404)

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Workflow

1. Define scope. Whole site, a subfolder, a migration check, or a specific issue.
2. Confirm access. What can you actually see (HTML, robots, sitemap, search console, server logs, staging)?
3. Crawl. Use a crawler to enumerate URLs and statuses. Sample if the site is huge.
4. Run the 6-layer framework. Score each, note specific issues with example URLs.
5. Cross-reference. Search console for what's actually indexed. Compare to sitemap and crawl output.
6. Prioritize. Critical (blocks indexing or causes traffic loss), Important (suboptimal), Nice-to-have (polish).
7. Write the report. Use the template in references/audit-template.md.

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Failure patterns

• Optimizing rankings on a page that is noindex. Always check indexability before content work.
• Adding sitemaps without fixing canonical issues. A sitemap of duplicate URLs is worse than no sitemap.
• Blocking crawlers from CSS or JS. Breaks Google's rendering. Common in over-aggressive robots.txt files.
• Over-relying on canonical tags. Canonicals are hints, not directives. Use redirects when content actually moved.
• Migrating without a redirect map. Single biggest cause of post-migration traffic loss.
• Treating Core Web Vitals as the only ranking signal. Page experience matters but does not override relevance.

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Output format

Default output is a markdown audit at seo-technical-audit.md. Structure:

1. Scope and methodology
2. Executive summary (3 to 5 critical findings)
3. 6-layer score
4. Critical issues (with example URLs)
5. Important issues
6. Nice-to-have polish
7. Implementation roadmap (sequenced)

For migrations, include a redirect map as a CSV alongside the report.

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If required data is unavailable

This skill's output depends on data, measurements, or tool results it cannot generate on its own. When a required input, tool, or data source is unavailable or unverifiable, the sanctioned output is the deliverable with the gap stated: what was needed, what was actually obtained or verified, and which parts of the output are affected. Fabricating, estimating, or interpolating a required number to complete the deliverable is never sanctioned. A stated gap is a complete answer.

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Reference files

• references/audit-template.md - Fillable technical SEO audit template.
• references/migration-checklist.md - Pre and post-migration checklist (covers the highest-risk scenario).