Free SEO Extension

DiagnoSEO is a free SEO Extension for Chrome and Firefox that delivers a complete on-page audit in one click — title, meta, canonical, headings, images, links, structured data, redirect chain, and a quantified 0-100 SEO score. It is the only SEO Extension (Chrome and Firefox) that also checks AI Overviews readiness (GEO) for ChatGPT, Perplexity, and Google AI Overviews.

Complete on-page SEO audit in one click

The Overview tab surfaces every important on-page SEO element at a glance:

• Quantified 0-100 SEO score with transparent deduction logic
• Title, meta description, and canonical URL with live character counts
• HTTP status code, meta robots, and X-Robots-Tag header detection
• Six half-grid checkpoints: word count, language, HTML source size, image counts

What does the DiagnoSEO SEO Extension do?

The DiagnoSEO SEO Extension (available for Chrome and Firefox) turns minutes of source-code inspection into a one-click on-page diagnosis. It surfaces every important SEO element: title with character count, meta description, canonical URL, meta robots, HTTP status code, X-Robots-Tag header, Open Graph and X (Twitter) cards, structured data (JSON-LD and microdata), hreflang with duplicate detection, viewport, charset, HTML lang attribute, and the full H1-H6 heading tree with collapsible navigation. The extension goes beyond inspection — it grades the page with a 0-100 SEO score using transparent deduction logic, runs a keyword placement check across more than 12 on-page locations, and is the only major SEO extension to include a dedicated GEO (Generative Engine Optimization) tab.

How DiagnoSEO helps SEO professionals and developers

• Comprehensive on-page checks across 8 organized tabs: Overview, Headings, Images, Links, Technical, Keyword, GEO, and Tools.
• 0-100 SEO score with transparent deduction logic. Compare pages, track improvements, and communicate page health to non-technical clients in one number.
• GEO / AI Overviews readiness — industry-first checks for /llms.txt, paragraph and sentence length, Organization / FAQPage / Article / speakable schema, and whether the first paragraph contains a number (a known LLM citation signal). No competitor offers this.
• Keyword placement checker with scored checks across title, H1, URL, first paragraph, headings, image alt text, image filenames, anchor text, and OG tags. Each check returns Exact / Partial / Missing with match highlighting in context.
• Redirect chain visualization with color-coded status badges (green for 2xx, orange for 3xx, red for 4xx/5xx) and bold arrows. Long chains (4+ hops) automatically escalate to issue level because they hurt crawl budget.
• Missing noopener detection — catches the reverse-tabnabbing risk on target="_blank" links without rel="noopener". No other major on-page SEO extension flags this.
• Orphan page detection — flags pages with zero internal links, since even one-page sites should link to at least a privacy policy.
• Interactive heading tree — color-coded H1-H6 badges with dashed connectors, collapsible chevrons on headings with children, double-click to highlight any heading directly on the live page.
• Real-time HTTP analysis — status code metric card, X-Robots-Tag header detection from the actual response (not the HTML), and full redirect tracing.
• 100% free forever — no paid tier, no usage caps, no premium upsells, no account required, no tracking. Your data never leaves your browser.

GEO and AI Overviews readiness

The GEO tab is industry-first — it checks every signal that AI search engines look for:

• /llms.txt and /llms-full.txt file detection (the emerging AI crawler standard)
• Organization, FAQPage, Article, and speakable schema validation
• Paragraph length (≤100 words) and sentence length (≤20 words) tuned for LLM parsing
• First paragraph number check — a known LLM citation signal for ChatGPT and Perplexity

Typical uses of the SEO Extension

• Run a full on-page audit in under 30 seconds for any URL — your own or a competitor's.
• Check whether a page is AI Overviews ready for ChatGPT, Perplexity, and Google AI Overviews.
• Score a target keyword's placement across every important on-page element.
• Diagnose indexing problems via meta robots, X-Robots-Tag, canonical, and status code in one glance.
• Inspect heading structure with a collapsible tree, find multiple H1s or empty headings instantly.
• Detect orphan pages and missing noopener on external links.
• Validate Open Graph and X (Twitter) Card metadata before publishing.
• Visualize redirect chains with color-coded status badges and bold arrows.
• Verify structured data, hreflang, viewport, charset, and HTML lang attributes.
• Highlight any heading or element directly on the live page with double-click.

Keyword placement audit across every on-page element

Type any keyword and see exactly where it lands across the page:

• Title, H1, URL, and meta description
• H2-H3 headings, image alt text, and image filenames
• Anchor text, body text density, and Open Graph tags
• Each check returns Exact / Partial / Missing with match highlighting and a weighted 0-100 keyword optimization score

DiagnoSEO compared with other popular SEO extensions

The table below compares DiagnoSEO with six of the most popular on-page SEO extensions: Detailed SEO Extension (by Ahrefs, 450,000+ weekly users), SEO META in 1 CLICK (by Florent Vilmart, established meta inspector), SEO Pro Extension (by MarketingSyrup, ~80,000+ weekly users), SEO Minion (now distributed via Keywords Everywhere paid plans), SEOquake (by Semrush, since 2006), and AITDK SEO Extension (newer entry, ~70,000 installs, 4.8 stars). The comparison reflects features publicly documented by each extension as of 2026.

The conclusion is clear. DiagnoSEO is the only SEO extension that offers a quantified 0-100 score, comprehensive keyword placement scoring with match highlighting, dedicated GEO / AI Overviews readiness checks, and an HTML vs rendered DOM diff. It also pioneered missing noopener and orphan page detection in this category. Each competitor has its own niche: Detailed SEO is the standard for external tool shortcuts, SEO Pro is the only one with Core Web Vitals, SEO META in 1 CLICK is the minimalist meta inspector, SEO Minion has unique SERP preview and location simulator (now bundled with Keywords Everywhere), SEOquake leads on SERP overlay and backlink integration, and AITDK adds traffic estimates and Whois.

Interactive H1-H6 heading tree

The Headings tab gives you a real tree visualization of your page structure:

• Color-coded badges from H1 (mint) to H6 (brown) with dashed tree connectors
• Collapsible chevrons on headings with children — drill into any section
• Multiple H1s, empty headings, and structural problems flagged automatically
• Double-click any heading to highlight it directly on the live page

Who DiagnoSEO is built for

• SEO consultants — run client audits in 30 seconds and communicate page health with a single score.
• In-house SEO teams — optimize landing pages and template-level improvements.
• Content marketers — check keyword placement and AI Overviews readiness before publishing.
• Web developers — verify canonical, structured data, hreflang, and accessibility issues during development.
• Agencies — validate client deliverables before sending reports.
• AI / GEO-focused marketers — optimize content for ChatGPT, Perplexity, and Google AI Overviews citations.

Privacy and pricing

DiagnoSEO is 100% free, forever. There is no paid tier, no usage caps, no premium upsells, and no account required. We do not track you, sell your data, or run analytics. The only network activity is reading HTTP headers from the page you are already viewing, a single favicon validation request, and two optional /llms.txt checks when you open the GEO tab. All of these go exclusively to the website you are currently on. Nothing ever reaches a DiagnoSEO server.

Internal, external, and redirect chain analysis

The Links tab breaks down every outbound link with security and SEO signals:

• 4×2 stat grid: Total, Internal, External, nofollow, sponsored, ugc, Empty anchor, Missing noopener
• Click any card to instantly filter the link list below
• Redirect chain visualization with color-coded status badges and bold arrows
• Long redirect chains (4+ hops) automatically escalate from warning to issue level

Frequently asked questions

• Is the DiagnoSEO SEO Extension really free?

  Yes. The extension is 100% free with no paid tier, no usage limits, and no account required. We do not collect any data, do not run analytics, and do not sell information to third parties.

• What makes DiagnoSEO different from Detailed SEO Extension?

  DiagnoSEO offers three features Detailed SEO does not include: a quantified 0-100 SEO score, a dedicated keyword placement checker with scoring, and a pioneering GEO / AI Overviews readiness tab. Detailed SEO remains stronger for external tool shortcuts.

• How is DiagnoSEO different from SEO META in 1 CLICK?

  SEO META in 1 CLICK is a lightweight metadata inspector focused on display. DiagnoSEO adds a quantified SEO score, keyword placement scoring, redirect chain visualization, schema inspection, hreflang validation, X-Robots-Tag detection, and GEO / AI Overviews readiness — none of which are in SEO META in 1 CLICK.

• How is DiagnoSEO different from SEO Pro Extension?

  SEO Pro Extension excels at Core Web Vitals field data and CSV export. DiagnoSEO offers a quantified 0-100 SEO score, comprehensive keyword placement scoring, GEO / AI Overviews readiness, missing noopener detection, empty anchor text warnings, and orphan page detection — none of which are in SEO Pro Extension.

• How is DiagnoSEO different from SEO Minion?

  SEO Minion is strong on SERP-side workflows: SERP preview, location simulator, PAA extraction. Some of its features moved behind a paid plan (~$70/year). DiagnoSEO stays 100% free and adds on-page depth: 0-100 SEO score, keyword placement scoring, GEO / AI Overviews tab, and HTML vs rendered DOM diff.

• How is DiagnoSEO different from SEOquake?

  SEOquake is built for off-page SERP intelligence: backlink overlay, multi-search-engine SERP metrics, Semrush integration. DiagnoSEO focuses on on-page audit and AI Overviews readiness with no Semrush ecosystem dependency. The two complement rather than replace each other.

• How is DiagnoSEO different from AITDK SEO Extension?

  AITDK bundles traffic estimates, Whois lookup, and on-page audit (Chrome-only). User reviews flag traffic-estimate accuracy issues. DiagnoSEO is on-page-only and reliable for that scope, works on both Chrome and Firefox, and adds GEO readiness and HTML vs rendered DOM diff.

• What is GEO and how is it different from SEO?

  GEO (Generative Engine Optimization) prepares your page for AI search engines like ChatGPT, Perplexity, and Google AI Overviews. DiagnoSEO is the only on-page SEO extension (Chrome and Firefox) that checks for llms.txt files, paragraph and sentence length tuned for LLM parsing, AI-friendly schema types (Organization, FAQPage, Article, speakable), and whether the first paragraph contains a number (a known LLM citation signal).

• Does the extension work on Single Page Applications?

  Yes. The extension includes a content script injection fallback that loads automatically on pages already open when the extension was installed, including React, Vue, Next.js, and other SPA frameworks.

• Does it work on protected browser pages?

  No. Browsers block all extensions on protected URLs such as chrome://, about:, the Chrome Web Store, addons.mozilla.org, and view-source pages. This is a browser security policy that applies to every extension on Chrome and Firefox, not a DiagnoSEO limitation.

• How is the 0-100 SEO score calculated?

  The score starts at 100 and deducts points for each detected issue using transparent rules. Major issues like a noindex meta deduct 30 points, an HTTP 4xx status deducts 40 points, and a missing title deducts 20 points. Minor issues like missing meta robots, empty headings, or empty anchor text deduct 1-2 points each (capped). The complete deduction table is documented in the extension.