Network & Files

Look up DNS records for a name, work out a subnet from a prefix, see the address and network this site sees your connection arriving from, and open a zip archive to inspect what is inside it before extracting anything.

Two of these are the site’s only exceptions to local processing, and they are labelled: a DNS query and reading your own address both require a server, so they are answered by this site’s own rather than by a third-party lookup service that would log your visit. Archive inspection is local, which is the safe way to look inside a zip you were sent before trusting its contents.

The other two read what a message or a response carries. Raw email headers hold the delivery chain with the delay at each hop, and the SPF, DKIM and DMARC results exactly as the receiving server recorded them — which is how you tell a forged sender from a real one. HTTP response headers hold the security and caching decisions a site has made, and reading them back is the quickest way to find the one that is missing. A .eml file holds the whole message — both bodies, every attachment and the MIME tree — and opening one here never fetches a remote image, so the sender learns nothing.

Then there are the three files that decide how a site is crawled and where its URLs go, none of which tells you it is wrong: a robots.txt rule blocks a URL you meant to keep, a sitemap.xml lists a relative URL or a malformed lastmod, an .htaccess redirect loops. Each of those is a rule you can only really check by running a URL through it and seeing which line fired — which is what these do. nginx has its own tester, which follows a request through server choice, location precedence and rewrite, hop after hop.

A MAC address rounds it out: five IEEE registries, what the address bits say about it, and the EUI-64 or IPv6 link-local form it becomes.

And a link rewritten by an email security service can be read without opening it: Microsoft 365 and Proofpoint protection links, redirects and the like unwrapped layer by layer to the address underneath, with the usual phishing tricks pointed out.

Email Header AnalyserPaste raw email headers: the delivery chain with the delay at each hop, SPF, DKIM and DMARC as the receiver recorded them, and who the message is really from.HTTP Header AnalyserPaste response headers and read them: security headers graded with what to change, caching explained in plain words, and every cookie flag checked.robots.txt TesterPaste a robots.txt and a list of URLs to see which are blocked for the crawler you pick, and exactly which rule and line decided it. Nothing is fetched.Sitemap Builder & ValidatorCheck a sitemap.xml against the sitemaps.org protocol, or build one from a list of URLs. Finds relative URLs, bad lastmod dates, mixed hosts and duplicates.MAC Address LookupLook up a MAC address in all five IEEE registries, read what the address bits say about it, and convert it to an EUI-64 or IPv6 link-local address.htaccess Redirect TesterPaste your .htaccess and a list of URLs to see the whole redirect chain, which rule and line fired, and where it loops. Apache only. Nothing is fetched.Email (.eml) ViewerOpen a .eml in your browser: headers, both bodies, every attachment and the MIME tree. Remote images are never fetched, so the sender is not told you looked.My IP & IP InspectorSee the IP address this site sees, with its network and rough location, and take any IPv4 or IPv6 address apart. No outside lookup service.DNS Lookup & Subnet CalculatorLook up A, AAAA, MX, TXT, NS and more through this site rather than your browser, and work out any IPv4 or IPv6 subnet. Ranges, masks and splits.Safe Link DecoderSee where a wrapped email link really goes: unwrap Microsoft 365, Proofpoint and other protection links and redirects, without opening them.nginx Redirect TesterPaste an nginx config and URLs: see which server and location take each request, what rewrite and return do, and every redirect hop, loop or 500.