Network Tools

When to use these tools

These are the tools for answering a question about a connection: why is this domain not resolving, what does my server actually return, is this certificate valid. DNS Lookup distinguishes the failure modes people usually conflate — NXDOMAIN means the name does not exist, while a NOERROR answer with no A record means it exists but has no address for that type, and the two point at entirely different problems. SSL Checker reads the presented chain so you can catch a hostname mismatch or an expiry date before your users do. HTTP Header Checker is how you verify what your server sends rather than what you intended it to send, which is the fastest way to confirm HSTS, CSP and cache-control are actually in effect. Redirect Checker traces the full chain, so you can see the hop where a 301 turns into an error page. IP Lookup returns the registered holder of an address block — worth reading the caveat on that page, because a city in the result is the registration location of the block, not the physical location of a person. Unlike every other category on this site, these lookups are proxied through our server because browsers block cross-origin requests; the values you enter are not stored or logged.