What are SANs (Subject Alternative Names)?

SANs list every hostname a certificate is valid for beyond its primary subject — for example, a certificate for example.com might also cover www.example.com and mail.example.com through its SAN list. Modern browsers rely on SANs rather than just the subject CN for validation.

Can I check SSL on a port other than 443?

Yes — this tool lets you specify any port, which is useful for checking certificates on mail servers (like port 465 or 587) or other non-standard HTTPS deployments.

Hostperl DNS Tools

SSL Certificate Checker

Check any domain's SSL/TLS certificate details including issuer, subject, validity dates, days until expiry, and SANs.

An expired or misconfigured SSL certificate breaks trust with visitors and can take a site offline in browsers. Run a quick check below before it becomes a problem.

Frequently asked questions

Browsers will show visitors a security warning and block easy access to the site until the certificate is renewed. Search engines and email systems may also treat the connection as untrusted, which can hurt both traffic and deliverability.