SEO Diagnostics

SEO Diagnostics audits a web page or an entire sitemap against a broad battery of checks, far wider
than a single Core Web Vitals or rich-results test. It loads each page in a real headless browser,
inspects the rendered DOM, measures performance, and grades the result. Progress streams live while
the audit runs, and a full categorised report is produced at the end.

Open it from the Tools menu, or go straight to /tools/seo. It is public: you do not need an
account.

Running an audit

  1. Paste a URL (for a single page) or a sitemap.xml URL.
  2. Choose Single URL or Sitemap. In sitemap mode, set how many pages to crawl (up to 50).
  3. Press Run audit. Progress appears immediately: each page is loaded, then every check runs.
  4. When the audit finishes, the score, grade, per-category breakdown and every individual check
    with its recommendation are shown. A link opens the full standalone report.

You can run one audit at a time. Targets that resolve to private or local addresses are refused.

What gets checked

The auditor groups its findings into categories:

  • Crawlability and indexing - HTTP status, redirect chains, HTTPS and HSTS, canonical tags,
    meta-robots and X-Robots-Tag, robots.txt, XML sitemap, URL hygiene, and mixed content.
  • On-page meta and content - title and meta description (presence and length), single H1 and
    heading hierarchy, content depth, language, character encoding, viewport, and favicon.
  • Links - internal and external link profile, descriptive anchor text.
  • Structured data - JSON-LD validity, recognised schema types and their required properties,
    microdata and RDFa detection.
  • Social cards - Open Graph and Twitter Card tags for rich link previews.
  • Performance and Core Web Vitals - Largest Contentful Paint, Cumulative Layout Shift, First
    Contentful Paint, Time To First Byte, page weight, request count, DOM size, compression, caching,
    image optimisation, and console errors.
  • Mobile and accessibility - responsive layout (no horizontal overflow), tap-target sizing,
    image alt coverage, and form labels.
  • Security - the common security response headers and TLS.
  • AI and LLM-search readiness - whether your primary content is in the initial HTML (server
    rendered) rather than JavaScript-only, presence of an llms.txt, and semantic HTML landmarks.

Each check reports a status (pass, warn, fail or info), its severity, the observed value, and a
recommendation when something can be improved. The overall score is a severity-weighted pass rate,
shown as a 0-100 number and an A to F grade, with a subscore per category.

Scoring

Failing a critical check (for example a non-200 status or HTTPS) costs far more than a low-severity
warning. Informational checks never affect the score. A score of 90 or above is an A.

Ask Devii

You can also run an audit in plain language through the Devii assistant:

Run SEO diagnostics on https://example.com and tell me the score.

Devii queues the audit, polls it, and reports the score, grade and a link to the full report.

Programmatic access

The same audit is available over the API: POST /tools/seo/run to queue, GET /tools/seo/{uid}
to poll, and GET /tools/seo/{uid}/report for the full report (HTML or JSON). See the
Tools (SEO Diagnostics) API group for request and response shapes.

Open SEO Diagnostics