What it checks

crawlie runs 57 rules and counting. Every finding links to plain-English guidance — why it matters, how to fix it, and what happens if you ignore it. Get that for any rule with crawlie explain <rule-id> (or the explain_issue MCP tool).

Technical SEO

Broken links · 4xx / 5xx · redirects & chains · titles & meta descriptions (missing / duplicate / length) · H1s · canonicals · noindex / nofollow / X-Robots-Tag · robots.txt blocking · images missing alt · thin & duplicate content · orphan & deep pages.

Representative rule ids: broken-link, client-error, server-error, redirect-chain, title-missing, title-too-long, title-duplicate, description-missing, description-duplicate, h1-missing, h1-multiple, canonical-missing, image-missing-alt, blocked-by-robots, thin-content, duplicate-content, low-text-ratio, content-requires-js, deep-page.

Performance & security

Slow responses · large pages · missing compression · HTTPS · mixed content · HSTS.

Rule ids: slow-response, large-page, no-compression, not-secure, mixed-content, no-hsts.

Accessibility (WCAG)

Static, false-positive-resistant accessibility checks — decided from the markup alone, no rendering or contrast analysis required. crawlie flags links and buttons with no accessible name (icon-only controls, empty aria-labels), form fields with no associated label (a placeholder isn’t a label), iframes missing a title, viewports that block pinch-zoom (user-scalable=no / low maximum-scale), positive tabindex values that hijack focus order, and headings that skip a level. These run on every HTML page, indexable or not.

Rule ids: a11y-link-no-text, a11y-button-no-text, a11y-input-no-label, a11y-zoom-disabled, a11y-iframe-no-title, a11y-positive-tabindex, a11y-skipped-heading.

Mobile, international & social

Viewport · lang · hreflang · Open Graph · Twitter cards · structured data.

Rule ids: viewport-missing, lang-missing, hreflang-incomplete, og-missing, twitter-missing, structured-data-missing.

Structured-data validation

Beyond detecting JSON-LD, crawlie parses it and validates each item against Google’s rich-result requirements — flagging markup that won’t earn a rich result. It catches JSON-LD that doesn’t parse at all, required properties that are missing (e.g. price on an Offer, image on a Product), and recommended properties worth adding — across Article, Product, Recipe, Event, FAQ, Breadcrumb, JobPosting, LocalBusiness, and more.

Rule ids: structured-data-invalid, schema-missing-required, schema-missing-recommended.

JavaScript rendering

Run a crawl with --render (CLI) or render: true (MCP) and crawlie audits each page from its post-JavaScript DOM via headless Chrome — so content, links and meta tags injected by React, Next.js, Vue and other client-rendered frameworks are seen, not missed. crawlie compares the raw server HTML with the rendered DOM and flags pages whose content only exists after JavaScript runs — a real risk, since Google renders JS on a delayed second pass and most AI answer engines don’t run it at all.

Rule id: content-requires-js.

GEO — Generative Engine Optimization

How citable your pages are by AI search like ChatGPT, Perplexity, and Google AI Overviews: structured data, semantic HTML, answer-readiness, authorship / E-E-A-T, dated content, question-style headings, and extractable blocks — rolled into a per-page GEO score.

Rule ids: geo-not-answerable, geo-no-structured-data, geo-no-semantic-html, geo-no-llms-txt, geo-no-author, geo-thin-for-ai, geo-ready.

Want the live, authoritative list? Run crawlie explain with no rule to print the full catalogue (CLI), or call the list_rules MCP tool — it reflects exactly what your installed version checks.