SSL Checker

The SSL Certificate Checker inspects the TLS certificate served by any HTTPS site or domain — showing you the issuer, valid-from and expiry dates, subject name and Subject Alternative Names (SANs), key algorithm and size, signature algorithm, and whether the certificate is trusted, self-signed or expired. It also flags certificates that are about to expire, use weak algorithms (SHA-1), or lack the correct SANs for the hostname.

SSL/TLS expiry is one of the top causes of unplanned outages — an expired certificate takes an entire service offline for every user until it's renewed. Automated monitoring (like this tool) is essential. Beyond expiry, you need to verify that the correct hostname is covered by the certificate's SANs — a common issue when adding new subdomains to a system with a manually renewed cert.

DevOps engineers, SREs, security teams and web admins run SSL checks continuously — either through automated monitors or on-demand when investigating an incident. Combine with our HTTP Headers tool to verify HSTS is set (which locks browsers to HTTPS for repeat visitors) and CAA-record lookup to confirm your issuance policy is correctly published.