Free Tools

Free SEO Tools for Prerendering &
JavaScript Sites

Seven browser-based diagnostics for JavaScript SEO: see how bots render your URL, verify prerendering, audit structured data, measure Core Web Vitals, and parse any sitemap. No sign-up, no quotas.

Prerender Checker

Verify your prerendering setup — fetches as Googlebot and confirms x-prerender-id header.

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Crawler Checker

See how Googlebot, GPTBot, ClaudeBot, and other bots actually render your URL.

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View as Bot

Compare no-JS HTML vs prerendered HTML side by side. Catch hidden indexation gaps.

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Quick SEO Audit

70+ technical checks: indexation, meta, structured data, security, performance.

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Core Web Vitals

LCP, CLS, INP measured for mobile + desktop using Google PageSpeed Insights.

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JSON-LD Validator

Verify schema.org markup blocks for rich-results eligibility and Google requirements.

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XML Sitemap Extractor

Parse any sitemap.xml (incl. sitemap-index) and group URLs by path. CSV export.

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Frequently Asked Questions

Are these SEO tools free?
Yes — every tool on this page runs in your browser, returns results immediately, and is free for unlimited use. There are no daily quotas, no premium tiers, and no paid features locked behind a sign-up. We make money from the underlying prerendering service (ostr.io), not from the tools themselves.
Do I need to sign up or create an account?
No account is required for any of the tools. Paste a URL, click run, get results. We do not require email, OAuth, or any other identification step before showing data.
Can I use these tools if I don't use ostr.io prerendering?
Absolutely. The Crawler Checker, Core Web Vitals, JSON-LD Validator, XML Sitemap Extractor, SEO Audit, and View-as-Bot tools all work on any public URL regardless of your hosting or rendering stack. The Prerender Checker is specifically designed to detect ostr.io setup, but it will also tell you when prerendering is not configured.
Do you store the URLs or data I submit?
We do not persist URLs or response bodies. Requests are made server-side to fetch the target page, results are returned to your browser, and the data is not stored. Aggregated, anonymous usage counts (e.g. "tool was used N times today") are tracked via standard analytics for capacity planning only.
How accurate is the data these tools return?
Tools fetch real HTTP responses using the exact User-Agent of each crawler (Googlebot, GPTBot, etc.) and parse the response with the same heuristics those bots use. Lighthouse-based metrics in Core Web Vitals are powered by Google PageSpeed Insights and match what Search Console reports. We always show the raw response so you can verify findings yourself.
Can I integrate these tools via API?
Direct API access is not exposed publicly today — the tools are wrappers around server actions used by the UI. If you need programmatic access for monitoring or CI, contact ostr.io support to discuss the prerendering analytics API, which provides per-bot crawl logs and verification data.

Background Reading

The why behind the tools — how rendering, crawlers, and prerendering middleware fit together.

Isometric prerendering SEO diagram showing bot, CDN, prerender cluster and origin server on a dark background
SEOFeatured

What Is Prerendering and Why Does It Matter for SEO

Learn how prerendering serves static HTML to search engine bots, solving JavaScript indexing problems and boosting organic traffic by up to 300%.

ostr.io Teamostr.io Team6 min·
Dark 3D comparison diagram of CSR, SSR, SSG and ISR columns for JavaScript SEO rendering
JavaScript

JavaScript Rendering for SEO: Complete Guide to CSR, SSR, SSG, and ISR

Compare four JavaScript rendering architectures and learn which one maximizes your SEO performance. Includes real-world benchmarks and decision framework.

ostr.io Teamostr.io Team6 min·
Dark isometric proxy and middleware cluster diagram showing bot traffic split between CDN and prerendering cluster
SEO

Pre-rendering Middleware Explained: Technical Architecture for SEO

Understand the technical architecture of pre-rendering middleware. Deploy Ostr.io to optimize JavaScript rendering and ensure immediate search engine indexation.

ostr.io Teamostr.io Team18 min·
Skip the diagnosis

Stop checking,
start prerendering

The tools above tell you what bots see. Ostr.io makes sure they see the right thing — fully rendered HTML, served from a co-located CDN, on every crawl.

Set up prerendering →