Security Tools
SSL Certificate Checker
Check a website's SSL/TLS certificate. See who it's issued to, who issued it, and how long until it expires.
Connects on port 443 (HTTPS). No port picker — this checks the standard HTTPS certificate only.
How it works
The tool opens a real TLS connection to the domain on port 443. This is the same handshake a browser performs. It reads back the certificate the server actually presents, and check whether it would be trusted by the standard set of certificate authorities that browsers rely on.
FAQ
- What does "Not trusted" mean?
- The certificate is expired, self-signed, issued for a different domain, or fails the same checks a real browser performs. That means visitors would see a warning page instead of a padlock. This tool connects anyway, so it can tell you why, instead of just refusing to check.
- Why does the expiry date matter so much?
- An expired certificate breaks HTTPS for every visitor. Browsers block the page completely instead of showing a warning people can click past. Most certificate outages happen simply because nobody renewed the certificate before it expired.
- What's the difference between "Issued to" and "Also valid for"?
- "Issued to" is the certificate's primary common name. "Also valid for" lists every extra hostname it covers, known as its Subject Alternative Names. Most certificates today cover several related domains or subdomains on one certificate.
- What do the protocol and cipher tell me?
- The protocol is which version of TLS was negotiated. TLS 1.3 and 1.2 are current, while TLS 1.0 and 1.1 are outdated and increasingly blocked by browsers. The cipher is which encryption algorithm is protecting the connection.