How to Check a Website's DNS, WHOIS, and SSL

Whether you’re launching a site, troubleshooting one that’s down, or sizing up a domain you might buy, three quick lookups answer most of your questions: DNS, WHOIS, and SSL. Here’s what each tells you and when to reach for it.

DNS — where the domain points

DNS (the Domain Name System) is the internet’s address book: it maps a domain like example.com to the servers that actually host its website and email. A DNS lookup shows a domain’s records:

• A / AAAA — the IP addresses the site lives on;
• MX — the mail servers that handle its email;
• TXT — verification and policy records (SPF, DKIM, domain-ownership checks);
• NS — the nameservers in charge of the domain.

If a new site “isn’t working yet” or email is bouncing, DNS is the first place to look.

WHOIS — who registered it, and when it expires

A WHOIS lookup reads the domain’s registration record: the registrar, when it was registered, when it expires, and its status. It’s how you check whether a domain is taken, catch a renewal you forgot, or see when an expiring name might become available. (Owners’ personal details are redacted on most domains now for privacy, so expect the registrar and technical record rather than a name.)

SSL — is the certificate valid and current?

The padlock in the browser comes from an SSL/TLS certificate. An SSL certificate check reads the public Certificate Transparency logs to show which certificates were issued for a hostname, who issued them, and when they expire — useful for catching a certificate that’s about to lapse (which would throw browser security warnings) or spotting one you didn’t request. One honest caveat: it reads the issued-certificate logs, not the live handshake, so it confirms what was issued rather than exactly what’s served this second.

A quick troubleshooting order

• Site won’t load at all? Check DNS first — is the A record pointing where it should?
• Browser shows a security warning? Check SSL — the certificate may be expired or mismatched.
• Wondering who’s behind it or when it renews? Check WHOIS.

All three run server-side against public records and store nothing about the domains you look up — so you can diagnose freely.