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About SSL Checker Online
This tool connects to any HTTPS endpoint and reports everything you need to know about its TLS configuration: certificate details (issuer, subject, expiration), supported protocols (TLS 1.2, 1.3), accepted cipher suites, certificate chain, and any common misconfigurations.
SSL/TLS checking is critical for security maintenance. Certificates expire — usually with no warning to the operator until users start seeing browser errors. Outdated TLS protocols (TLS 1.0, 1.1) leave you vulnerable to known attacks. Weak cipher suites enable man-in-the-middle compromises.
Use it after deploying any new HTTPS service, before a certificate renewal, when migrating between hosting providers, or as part of a regular security audit.
How to use this tool
How to inspect a host's TLS certificate
Enter the hostname
Type the host (e.g. example.com) into the Hostname field. Up to 253 characters. SNI is set from this name.
Pick the port
Port defaults to 443 (HTTPS). Use 465 for SMTPS, 993 for IMAPS, 995 for POP3S, etc. — anything that speaks TLS at connect time.
Press Run
Our server opens a TLS connection with SNI = Hostname and rejectUnauthorized: false (so expired/self-signed certs still produce a readout), reads the peer certificate, then closes the socket.
Read the certificate
Output covers subject, issuer, validFrom / validTo, SANs (subject alternative names), fingerprint, key algorithm, and serial number. Mismatched SAN or expired dates are common causes of "NET::ERR_CERT…" errors in browsers.