# Web Validators / SEO Tech Tests > Free web validation and technical SEO testing tools. ## Web Validators - [HTML Validator](https://seotechtests.com/html-validator): Check HTML for spec errors, accessibility problems, and SEO markup issues. - [CSS Validator](https://seotechtests.com/css-validator): Find invalid properties, malformed selectors, and unknown values in CSS. - [JSON Validator](https://seotechtests.com/json-validator): Validate, format, and minify JSON with precise error locations. - [XML Validator](https://seotechtests.com/xml-validator): Check XML for well-formedness issues like unclosed or mismatched tags. - [Image Metadata Validator](https://seotechtests.com/image-metadata-validator): Check an image's EXIF, IPTC, and XMP metadata against the IPTC Photo Metadata Standard, including rights and Google Images support. ## HTTP & Crawling - [HTTP Status Checker](https://seotechtests.com/http-status-checker): Check HTTP status codes, redirect chains, and server responses for multiple URLs. - [Response Stability Test](https://seotechtests.com/response-stability-test): Run up to 20 sequential requests to check HTTP status, latency and response consistency. - [Redirect Matrix](https://seotechtests.com/redirect-matrix): Test http/https and www/non-www host variants, follow every redirect hop, and compare destinations across browser and crawler User-Agents. - [HTTP Methods](https://seotechtests.com/http-methods): Compare GET, HEAD, and OPTIONS responses for the same URL to spot method-specific status, redirect, and header mismatches. - [Cache Behavior](https://seotechtests.com/cache-behavior): Send a small controlled sequence of repeated requests to observe cache status transitions, ETag stability, and Cache-Control consistency. - [Conditional Requests](https://seotechtests.com/conditional-requests): Test If-None-Match and If-Modified-Since against a URL's own ETag and Last-Modified headers to verify 304 Not Modified support. - [Security Headers](https://seotechtests.com/security-headers): Semantic analysis of CSP, HSTS, and other security headers, including GET vs HEAD parity and redirect-chain behavior -- not just presence checks. - [Content Negotiation](https://seotechtests.com/content-negotiation): Test HTTP content negotiation by sending different Accept headers (HTML, Markdown, JSON, XHTML, */*) and comparing the responses. - [Compression & Encoding](https://seotechtests.com/compression): Compare identity, gzip, Brotli, and Zstandard representations of a URL to measure real compression ratios and detect malformed encoded responses. ## SEO Tests - [Meta Tag Checker](https://seotechtests.com/meta-checker): Inspect a page's title, description, canonical, and other metadata. - [Open Graph Checker](https://seotechtests.com/open-graph-checker): Preview how a page will look when shared on social platforms. - [Robots.txt Checker](https://seotechtests.com/robots-checker): Fetch and parse a domain's robots.txt for issues and conflicts. ## AI & Crawlers - [AI Agent Readiness Checker](https://seotechtests.com/ai-agent-readiness-checker): Check whether a website exposes the files, headers, crawler rules and emerging protocols used by AI agents. - [User-Agent Checker](https://seotechtests.com/user-agent-checker): Compare HTTP responses for browser, search crawler and AI User-Agent profiles. ## Accessibility - [Accessibility Checker](https://seotechtests.com/accessibility-checker): Run automated accessibility checks against a live page with axe-core. ## Domain Security - [Domain Security Score](https://seotechtests.com/domain-security-score): One weighted 0-100 score combining malware/phishing reputation, spam/abuse, infrastructure, transport security, DNS security, registration, popularity, and authority signals. - [HSTS Preload](https://seotechtests.com/hsts-preload-checker): Whether the domain is on the browser HSTS preload list. - [Cloudflare Radar Domain Ranking](https://seotechtests.com/cloudflare-radar-domain-ranking-checker): Cloudflare Radar's domain categorization, read for malicious-category flags. - [VirusTotal](https://seotechtests.com/virustotal-checker): Aggregated malware/phishing verdicts from dozens of security vendors. - [Google Web Risk](https://seotechtests.com/google-web-risk-checker): Google Cloud's Web Risk Lookup API, checked for malware, social engineering, and unwanted software matches. - [Spamhaus](https://seotechtests.com/spamhaus-checker): Spamhaus Domain Block List (DBL) lookup for spam/malware-associated domains. - [URLhaus](https://seotechtests.com/urlhaus-checker): abuse.ch's database of malware-distribution URLs hosted on this domain. - [AbuseIPDB](https://seotechtests.com/abuseipdb-checker): Abuse reports against the domain's hosting IP address. - [DNSBL / RBL](https://seotechtests.com/dnsbl-rbl-checker): General-purpose DNS-based real-time blocklist lookup against the domain's IP. - [SURBL](https://seotechtests.com/surbl-checker): SURBL multi-list domain reputation lookup. - [URIBL](https://seotechtests.com/uribl-checker): URIBL multi-list domain reputation lookup. - [PhishTank](https://seotechtests.com/phishtank-checker): Community-verified phishing URL database. - [TLD Spam / Abuse Ranking](https://seotechtests.com/tld-spam-abuse-ranking-checker): Aggregate spam/abuse rate for the domain's top-level domain. - [ICANN Domain Metrica](https://seotechtests.com/icann-domain-metrica-checker): ICANN's aggregated abuse-feed and popularity data for this domain. - [Spamhaus Intelligence API](https://seotechtests.com/spamhaus-intelligence-api-checker): Spamhaus's proprietary reputation score, blocklist listing status, and threat tags via their Intelligence API. - [DNSSEC](https://seotechtests.com/dnssec-checker): Whether DNS responses for this domain are cryptographically signed and validated. - [CAA](https://seotechtests.com/caa-checker): Which Certificate Authorities are authorized to issue certificates for this domain. - [SPF](https://seotechtests.com/spf-checker): Which mail servers are authorized to send mail as this domain. - [DKIM](https://seotechtests.com/dkim-checker): Cryptographic signing keys for outbound mail, checked against common selectors. - [DMARC](https://seotechtests.com/dmarc-checker): Policy telling mail receivers what to do with mail that fails SPF/DKIM. - [MTA-STS](https://seotechtests.com/mta-sts-checker): Whether inbound mail transport is required to use authenticated TLS. - [TLS-RPT](https://seotechtests.com/tls-rpt-checker): Whether failed TLS mail delivery attempts are reported. - [SSL/TLS](https://seotechtests.com/ssl-tls-checker): Certificate validity, expiry, and negotiated TLS protocol version. - [Advanced TLS Checker](https://seotechtests.com/ssl-labs-checker): SEOTechTests' own advanced TLS/SSL configuration assessment -- certificate, protocols, cryptography, and configuration findings. - [Certificate Transparency](https://seotechtests.com/certificate-transparency-checker): Public CT log history for certificates issued to this domain. - [CSP](https://seotechtests.com/csp-checker): Content-Security-Policy presence and directive analysis. - [Mixed Content](https://seotechtests.com/mixed-content-checker): Hard-coded http:// resource references on an HTTPS page. - [security.txt](https://seotechtests.com/security-txt-checker): RFC 9116 security.txt vulnerability-disclosure contact file. - [Domain Age](https://seotechtests.com/domain-age-checker): How long ago this domain was registered, via RDAP. - [RDAP / Registrar](https://seotechtests.com/rdap-registrar-checker): Registrar and registration data via the RDAP protocol. - [Domain Registration Status](https://seotechtests.com/domain-registration-status-checker): EPP status codes revealing holds, pending deletion, or transfer locks. - [Nameservers](https://seotechtests.com/nameservers-checker): Configured nameservers and basic redundancy check. - [Hosting ASN](https://seotechtests.com/hosting-asn-checker): Which network (Autonomous System) hosts this domain. - [IP Reputation](https://seotechtests.com/ip-reputation-checker): Abuse history of the domain's hosting IP address. - [Tranco Rank](https://seotechtests.com/tranco-rank-checker): Independent, research-grade domain popularity ranking. - [Cloudflare Radar Rank](https://seotechtests.com/cloudflare-radar-rank-checker): Cloudflare's own traffic-based domain popularity rank. ## Optional - [Full Documentation](https://seotechtests.com/llms-full.txt): Detailed overview of all tools and features. - [Sitemap](https://seotechtests.com/sitemap.xml): Complete XML sitemap listing all pages.