SEO Structural Audit

Overview

Most "SEO problems" that look like content problems are actually structural — a missing canonical, a sitemap that 404s, a hero rendered only after JS hydration that Googlebot can't see, schema that fails validation, a redirect chain that drains link equity. This skill is the diagnostic playbook for that layer: a fetch protocol that gets the evidence in parallel, a per-surface check rubric that turns the evidence into a finding, and a severity matrix that says what to fix first. Output is a prioritized list with cited evidence — never inference where evidence could have been fetched.

Mental model

Structural SEO is a chain of pass-throughs:

1. The crawler can reach the URL (robots.txt allows; no infinite redirect; status 200).
2. The renderer can see the content (raw HTML carries primary content OR pre-rendered; JS hydration doesn't hide it).
3. The indexer can understand the page (meta robots indexable; canonical self-referential or correctly assigned; schema validates).
4. The ranking system can compare it (Core Web Vitals within thresholds; internal-link topology lets PageRank flow; hreflang resolves correctly per locale).

Break any link in the chain and rankings collapse downstream regardless of how good the content is. Audit walks the chain in order; the first broken link is the highest-priority finding.

Instructions

Fetch protocol (parallel, ONE block)

Before scoring anything, get the evidence:

• webfetch the target URL — capture HTML, response headers, render the page if JS-heavy.
• shell curl -sI <url> — capture raw HTTP response and follow redirect chain (-L with -w "%{redirect_url}\n%{http_code}\n").
• shell curl -s <origin>/robots.txt — fetch robots, parse Allow / Disallow / Sitemap: directives.
• shell curl -s <origin>/sitemap.xml — fetch sitemap; check for index file vs flat sitemap; spot-validate 5–10 URLs.
• websearch site:<domain> — sanity-check indexed page count and freshness.
• For JS-rendered sites: compare webfetch raw HTML vs a rendered fetch (skill references/render-parity-check.md if needed).

Run all six in one tool block. Don't serialize. If any fetch fails, the result becomes an "Unverified" finding — never inferred.

Check rubric (per surface)

Severity matrix

• Critical — blocks indexing, blocks rendering, creates indexability conflict, or hits the "poor" CWV band. Fix before anything else.
• Moderate — degrades signal (chain too long, schema missing on eligible page, "needs improvement" CWV). Fix in current cycle.
• Minor — polish (slug aesthetics, alt-text on decorative images, sitemap last-modified timestamp accuracy). Fix when convenient.

A Critical finding stays Critical even when "it's just one tag." Severity is impact-weighted, not effort-weighted.

Unverified checks — escalation rule

If a check could not run:

• 403 on robots.txt or sitemap → "Unverified: server blocks unauthenticated fetch; ask for crawler-allowed IP or share via GSC export."
• JS-render parity untestable (no headless browser available) → "Unverified: render parity needs headless render; recommend a Lighthouse run or rendered-fetch sample."
• GSC data needed (impressions, indexed-page count, crawl errors) → "Unverified: GSC access required; share read-only access or paste a coverage report."

Never infer a finding from absence of evidence. "Could not fetch" is its own finding type — it tells the user what to unblock, and it preserves trust in the rest of the report.

Schema validation notes

• FAQ schema → check mainEntity array, each Question has acceptedAnswer.Answer.text. Highest single-impact schema for AI citation eligibility.
• Article schema → headline, author (Person with name + optional sameAs/url), datePublished, dateModified, description. Missing author on a YMYL page is a Critical-tier finding (March 2026 amplified author-credential signal — 73% of post-update YMYL top results display detailed author credentials, up from 58%).
• Person / Organization schema → required to anchor entity recognition for E-E-A-T. Missing sameAs outbound to LinkedIn / publication / org bio is Moderate.
• HowTo schema → step array with name + text per step. Cited for procedural queries.
• Review / AggregateRating → present only when genuine reviews back it; fake review-schema is a manual-action trigger.

Core Web Vitals — interpretation, not measurement

This skill interprets CWV; it does not measure them. Source measurements:

• Field data: Google PageSpeed Insights, Search Console Core Web Vitals report, CrUX dataset.
• Lab data: Lighthouse CLI (shell capability), WebPageTest, browser DevTools.

When only lab data is available, flag the field-vs-lab gap; lab overstates good performance in many cases. INP needs field data — lab-only INP estimates are unreliable.

Internal-link topology — what to look for

• Pillar pages should link out to every cluster article in their opening section (first 200 words).
• Cluster articles should link back to the pillar within the first 100 words.
• Cluster siblings should cross-link 2–3 times where topically relevant.
• Every indexable page should be reachable within 3 clicks from the homepage.
• Orphan pages (no internal inbound links) are a Moderate finding — they signal abandoned content or template gaps.
• The link graph should mirror the topic graph, not the navigation hierarchy.

Output

Use the canonical output structure from the agent that runs this skill. Every finding includes: severity, evidence (URL + line / header / schema field / metric), why it matters, fix direction. Save as seo-audit-[slug]-[YYYY-MM-DD].md in working directory.

Checklist

• All six fetch operations ran in parallel
• Every check in the rubric was evaluated or flagged as Unverified
• Each finding cites concrete evidence (URL, line, header, schema field, metric)
• Severity assigned by impact, not effort
• Unverified findings name the specific blocker and the unblock path
• Schema findings name the type and the missing/invalid field
• CWV findings name the source (field / lab / PSI) and the band (good / needs improvement / poor)
• Internal-link topology checked for pillar/cluster pattern and orphan pages
• Report saved to disk with timestamped filename

Composition / References

Within-domain pairings:

• Pairs with the sibling SEO skill that audits on-page content quality (titles, meta, headings, intent match, AI-citability, E-E-A-T).
• Pairs with the sibling SEO skill that audits link profile (referring-domain quality, anchor distribution, toxic neighborhoods).

External authoritative sources:

• Google Search Central — Crawling and indexing
• Google Search Central — Structured data general guidelines
• Google Search Central — Core Web Vitals
• Schema.org — full type vocabulary
• web.dev — INP
• Google Search Central — hreflang