View full cert chain, expiry, SANs, issuer. Free SSL certificate checker.
The SSL Certificate Checker connects to a domain and reports certificate details: issuer, subject, validity dates, Subject Alternative Names (SANs), and the full chain from the server certificate through intermediates to a trusted root. Use it to verify production certificates, debug invalid or expired cert errors, and plan renewals. The tool runs from our server so you can check any public domain. It helps you confirm that the correct certificate is deployed, that the chain is complete and trusted by major browsers, and that no hostname mismatches or expiry issues will affect users. Many connection errors in browsers (e.g. NET::ERR_CERT_AUTHORITY_INVALID or ERR_SSL_VERSION_OR_CIPHER_MISMATCH) can be diagnosed by inspecting the chain and validity with this checker.
The chain from your server cert through intermediate CA certs to a root CA. Browsers validate the full chain to trust your certificate.
The certificate was issued for a different name than the one you requested. Get a cert that includes your domain in the subject or SAN.
Renew with your Certificate Authority and install the new cert on your server. Set a reminder before the next expiry date.
Certificate and TLS version are related but separate. Use a TLS version checker to see which protocol versions the server supports.
Most checkers use port 443. For other ports you may need a CLI tool or a checker that supports custom ports.