Free tool
SSL certificate checker
See when a certificate expires, who issued it, and whether browsers trust it. For a port other than 443, add it after the name, like example.com:8443.
What the checker looks at
Expiry date
When the certificate ends and how many days are left. 30 days or less shows as expiring.
Trust
Whether a browser would accept it: trusted issuer, full chain, and a name that matches the domain.
Connection
Whether the server answers on that port with TLS 1.2 or newer and presents a certificate.