SSL Certificate Checker

SSL Certificate Checker

This tool opens a live TLS connection to a domain on port 443, retrieves the certificate the server actually presents, and lays out what matters: who issued it, who it's for, when it expires, and which hostnames it covers.

What you're looking at

• Subject / SAN — the names the certificate is valid for. Modern certificates cover their hostnames in the Subject Alternative Name list, not the legacy Common Name. A mismatch here is why browsers throw "your connection is not private".
• Issuer — the Certificate Authority that signed it. A trusted public CA (Let's Encrypt, DigiCert, Google Trust Services…) is what makes the padlock appear.
• Validity window & expiry — certificates are short-lived by design now (often 90 days). An expired certificate breaks every client immediately, so the expiry countdown is the single most operationally important field.
• Fingerprint / serial — the certificate's identity, useful for pinning and for confirming you're seeing the cert you expect.

Why it matters

Expired certificates are one of the most common self-inflicted outages on the internet. Beyond expiry, checking the presented certificate reveals mis-issued or wrong-host certificates, weak signature algorithms, and misconfigured chains. Because this tool connects and reads the actual presented certificate rather than a cached record, it reflects reality right now.

Note on scope

This inspects the leaf certificate the server presents. It does not perform full chain-of-trust or revocation validation — use it for expiry monitoring, host/SAN verification, and issuer confirmation.