Audit and monitor any domain.
One paste checks DNS, email, TLS and crawler posture. Verify the domain and we keep watching — and tell you what changed.
Try: stripe.com · openai.com · cloudflare.com
Every protocol, every probe.
Each tool wraps a real protocol query — DoH, DNS, WHOIS port 43, TLS handshake, ICMP-style timing, CT logs, robots.txt parsing — with a result panel you can read, copy, or scrape. JSON or Markdown on every endpoint, no rate limits on the public UI.
Most diagnostic sites stop at DNS. We also check whether GPTBot can read you, whether llms.txt is published, and whether your pages are structurally citable by Claude, Perplexity and ChatGPT.
DNS & domain
Resolve, audit, and compare records across global resolvers.
Query A, AAAA, MX, NS, TXT records from Google, Cloudflare, Quad9, and OpenDNS in parallel.
DNS LookupEvery common record type for a domain on one page — A, AAAA, CNAME, MX, NS, TXT, SOA.
Reverse DNSPTR record lookup with forward-confirmed reverse DNS (FCrDNS) verification.
WHOIS LookupRegistrar, creation/expiry dates, status codes, and name servers — with referral following.
DNS PropagationQuery 12 free public DNS resolvers in parallel; spot inconsistencies during a migration.
Domain AgeHow long has this domain been registered? Derived from WHOIS creation date.
Email deliverability
The records receivers actually use to score your mail.
Mail servers, SPF posture, and DMARC policy for any domain — in one shot.
IP Blacklist CheckCheck an IP against Spamhaus ZEN, Barracuda, SpamCop, SORBS, UCEPROTECT and 6 more active RBLs.
DMARC AnalyzerFetch the DMARC record at _dmarc.<domain> and grade its strength (p=, sp=, pct=, rua=).
Look up the DKIM public key at <selector>._domainkey.<domain>. Common selectors tried automatically.
Syntax check (RFC 5322) + MX lookup + disposable-domain detection for any address.
IP & network
See what the rest of the internet sees, and look up any address.
Your public IPv4 and IPv6 with ISP, ASN, and approximate geolocation.
IP LookupGeolocation, autonomous system, and abuse contact for any IPv4 or IPv6 address.
Speed TestDownload, upload, ping, and jitter measured against our streaming endpoints.
Cloud Region DetectorMap any IP to its AWS, GCP, Azure, Cloudflare, Fastly, or Akamai region.
TLS & HTTP security
Inspect certificates and response headers from the browser.
Subject, issuer, validity dates, SAN list, signature algorithm, and days-to-expiry.
HTTP Header InspectorFull response headers plus a security-headers audit (HSTS, CSP, XFO). SSRF-guarded.
Subdomain EnumeratorDiscover subdomains via Certificate Transparency logs (crt.sh). No API key needed.
HTTP/2 + HTTP/3 TestNegotiate HTTP/1.1, HTTP/2, and HTTP/3 against any host; report what worked.
Tech DetectorIdentify the CMS, framework, analytics, CDN, and ecommerce stack of any public site.
Crawler & AEO controls
Audit how search engines, sitemaps and AI agents see your site.
Parse robots.txt — flag invalid lines, show user-agent precedence, list declared sitemaps.
Sitemap.xml ValidatorFetch + validate any sitemap.xml. URL count, lastmod freshness, sitemap-index recursion.
AEO CheckerScore answer-engine readiness: llms.txt, AI-bot posture, JSON-LD coverage, FAQ/HowTo schemas.
AI Crawler ValidatorParse robots.txt for 15+ AI bot UAs (GPTBot, ClaudeBot, PerplexityBot, etc.) and recommend posture.
Built like a tool you'd reach for from the terminal.
Most "diagnostic" sites are SEO farms wrapped around fake data. This one runs the actual queries and shows you what comes back.
Real queries
DoH for DNS, RFC 3912 WHOIS on port 43, TLS handshake for SSL, parallel curl for HTTP. Same answers a sysadmin would get.
Privacy-first
No third-party analytics and no ad trackers. Fonts and scripts are served from our own origin, so running a check doesn't hand your pageview to anyone else. Every tool works without an account, and IP addresses on speed-test runs are deleted after 90 days.
JSON API on every tool
Every tool is also a REST endpoint. 100 calls/day free, paid plans for higher volume. Read the docs →
Mobile-ready
Every page is built mobile-first. Run a DNS check from your phone and the result panel actually fits on the screen.
Field notes for the toolkit
How DNS actually propagates, why your mail lands in spam, what an SSL cert really tells you. Practitioner-level guides.
A practical guide to DNS resolution: how queries flow, what each record type does, and why "propagation" isn't really propagation.
August 23, 2026 Why Your Email Lands in Spam: SPF, DKIM, DMARC, and IP ReputationMost email deliverability problems are about authentication and reputation, not content. Here's the practical playbook for SPF, DKIM,...
August 23, 2026 How to Read an SSL/TLS Certificate (Without the Jargon)A practical guide to TLS certificates: SANs, chains, validity windows, OCSP stapling, and the errors you'll actually see in browsers.
August 23, 2026 What Your IP Address Actually Reveals (and What It Doesn't)A clear-eyed explainer of what an IP address actually exposes: ISP, ASN, approximate location, and the limits of geolocation, plus how VPNs...
August 23, 2026Need scheduled monitoring + bulk lookups?
Pro monitors 50 domains, swept once a day across every host on the domain, and adds bulk CSV lookups, audit history with diff view, a 50k-call/day API, and zero ads.
See pricing →