SSL Certificate Checker
Inspect SSL/TLS certificate chains, SANs, cipher suites, and expiration warnings.
About TLS certificates
This tool connects to a host and reads its TLS certificate. It shows the subject, the issuer, the validity dates, the alternative names, and the cipher suite.
The most common failure is an expired certificate. The second is a missing name: the certificate must list the exact host name in its subject alternative names, so a certificate for example.com does not cover www.example.com.
Check the chain as well. A server must send the intermediate certificates. A browser often hides a missing intermediate, and a command line client or a mobile app then fails.