Free SEO tools.
The toolkit we use in-house, open to everyone. No disguised freemium, no email required to see results. You paste, you get the answer.
Snippets & SERP
Visualize and prep the Google presentation before publishing.
Structured data
Generate and validate Schema.org / JSON-LD markup.
Schema.org JSON-LD Generator
Produce valid Schema.org JSON-LD markup for Article, Product, FAQ, Breadcrumb, LocalBusiness, Organization, HowTo, Recipe, Event, VideoObject, Review, and Person.
Schema.org Validator
Paste your JSON-LD: schema.org structural validation, required and recommended fields checked, common errors flagged. 12 types supported.
Linking
Audit a backlink profile quality, anchor diversity, internal linking.
Backlink Anchor Audit
Paste your backlink anchors and measure their diversity: brand, naked URL, exact match, long-tail, generic. Auto-detects over-optimization.
Domain Age & WHOIS
Domain creation date, registrar, nameservers, status. Official RDAP data to evaluate a domain before purchase or before posting a backlink on it.
Outbound Links Audit
Before buying a backlink on a page, check it's not a link farm. Counts dofollow vs nofollow, internal/external ratio, density per 1000 words, top destinations.
Hidden Text Detector
Before buying a backlink, scan the host page for CSS-hidden links: display:none, visibility:hidden, font-size:0, negative text-indent. Classic PBN pattern.
Sellable URL — eligibility
Is a URL eligible to receive an editorial backlink? Score 0-100 across 7 axes: indexability, substance, structure, links, brand, cleanliness, freshness.
Internal Linking Opportunities
Paste a host URL + target keywords: find existing paragraphs that mention your KWs without linking yet. Editorial anchors ready to place.
Internal PageRank Simulator
Compute your site's internal PageRank from an edge CSV: real hubs, orphan pages, dead-ends, Gini distribution. Configurable damping factor and iterations.
Backlink Quality Scorer
0-100 authority score of a URL via DataForSEO live: dofollow RD, Link Rank, broken-link ratio. 10 req/day.
Anchor Profile from URL
Fetch real anchors pointing to a URL via DataForSEO + brand/exact/partial/generic classification + Penguin risk score. 10 req/day.
Editorial content
Measure readability, extract metas in bulk, audit what your pages really say.
Readability Analyzer
Measure your English text readability: Flesch Reading Ease, Gunning Fog, long sentences, lexical diversity, complex words. Calibrate tone to your audience.
Bulk Meta Extractor
Extract title, meta description, H1 and H2 from up to 50 pages at once. Ideal for auditing the editorial consistency of a category or a competitor.
A/B Test SEO Calculator
Measure whether the gap between two variants (titles, layouts, snippets) is statistically significant. Two-proportion Z-test with p-value and confidence interval.
Page E-A-T Profile
E-A-T score based on objective signals: identified author, published and modified dates, citations to authority sources, Article+Person Schema.org markup.
AI Overview Readiness
Is your page ready for AI Overviews and ChatGPT Search? FAQ/HowTo schema, Q&A pattern, lists, direct answer, brand mentions — score 0-100.
Duplicate Content Detector
Compare 2 URLs: Jaccard shingle similarity on 4-grams. Verdict identical / near-duplicate / derived / original.
Semantic Cocoon Generator
Hierarchical clustering on cosine of bag-of-words: turns a raw KW list into a pillar → clusters → leaves plan. To structure a silo before writing.
TF Gap Analysis
Compare your URL to 1-5 competitors: terms they use and you don't (semantic gaps), terms unique to your page, entity bigrams.
Technical SEO
Inspect robots, hreflang, canonical, headers — the plumbing that decides indexing.
robots.txt Multi-Bot Tester
Test your robots.txt against 18 user-agents: Googlebot, Bingbot, GPTBot, ClaudeBot, PerplexityBot, Applebot and other AI crawlers. Path × bot matrix.
hreflang Tester
Verify your hreflang tags: valid ISO codes, reciprocity between language versions, x-default, conformance with Google's recommendations.
HTTP Headers SEO Checker
Inspect HTTP response headers: x-robots-tag, cache-control, HSTS, link, vary, server. SEO + security annotations on impactful headers.
sitemap.xml Validator
Validate your sitemap.xml: structure, URL count, lastmod outliers, sitemap-index recursion. Conforms to sitemaps.org and Google.
Bulk Status Code Checker
Test up to 200 URLs at once: HTTP code, redirect chain, response time. Ideal for backlink profile audits.
Canonical Chain Checker
Audit a URL's canonical tags: self-canonical, canonical chain, HTML vs HTTP header conflict, loop detection.
HTTPS Mixed Content Checker
Detect HTTP resources served on an HTTPS page: images, scripts, iframes, fonts. Silent cause of "not secure" warnings and user-trust loss.
Heavy Resources Detector
Detect images, scripts, videos and CSS files over 2 MB on a page — the resources Google struggles to crawl and that wreck your crawl budget.
Indexability Verdict
One URL, one verdict: indexable or not, and if not, why exactly. Combines HTTP status, robots.txt, meta robots, X-Robots-Tag, canonical chain and hreflang into a single check.
Googlebot vs Chrome Diff
Compare what Googlebot sees vs a regular browser. Detects cloaking, JS-only renders, and content served differently by user-agent.
Soft 404 Detector
A page returns 200 but displays "page not found"? Soft 404s fool standard tools but wreck your indexing. This tool hunts them explicitly.
TTFB, Protocol & Compression
Three perf measures in one check: server Time To First Byte, HTTP version (1.1 / 2 / 3), Brotli or gzip compression detected. Quick sniper to flag a slow or misconfigured server.
Lazy-Load Above the Fold
Detects <code>loading="lazy"</code> images visible immediately on screen. Silent LCP killer — Google penalizes mechanically.
Core Web Vitals Checker
LCP, INP, CLS + Lighthouse score for any URL via Google PSI API. Mobile vs desktop choice.
More tools coming
AI bot robots.txt tester, hreflang validator, internal linking audit, PageRank simulator, backlink quality scorer. The public roadmap is on GitHub.
See the roadmapBeyond the tools?
Stringer is a network of publisher sites selling backlinks direct. Public catalog, publisher pricing shown, no commission, no opaque marketplace.