SSL Certificate Checker

The tool checks a website's SSL/TLS certificate by domain name and shows all the key information about the connection's security. The service connects to the server over HTTPS on port 443, retrieves the certificate, and breaks it down into its components: the issuing certificate authority, validity period (issue and expiration dates), serial number, signature algorithm, and the domain's Common Name.

Besides the main certificate, the check shows the full chain of trust - the intermediate and root certificates that confirm the authenticity of the site's SSL certificate. It also displays the domain's Subject Alternative Names (SAN), the server's IP address, and the Server header, which can be used to identify the type of web server in use.

Checking the certificate helps catch an expiring SSL certificate, chain validation errors, or a domain mismatch in the certificate in time. Registered users can add a domain to monitoring and receive notifications when the certificate is about to expire, as well as save check results to their history.