SSL Certificate Checker

SSL Certificate Checker connects to a domain over HTTPS and inspects the TLS certificate it presents, reporting whether the certificate is valid, who issued it, and exactly when it expires. It surfaces the key details that determine trust: the common name and any Subject Alternative Names (the hostnames the certificate covers), the issuing certificate authority, the validity window with start and end dates, and the days remaining before expiration. This gives you a quick, authoritative answer about whether a site's encryption is currently trustworthy.

The check works by completing a TLS handshake with the server, retrieving the certificate chain, and validating it the way a browser would. That means confirming the certificate is within its validity dates, that the hostname matches one of the names on the certificate, and that the chain links up to a trusted root authority. The tool also typically reports the intermediate certificates, which is important because a missing intermediate is one of the most common reasons a certificate that looks valid in one client fails in another.

The most common use case is monitoring expiration so a certificate never lapses and triggers browser warnings that scare away visitors. Teams also use it to verify a freshly installed certificate covers the right hostnames, to confirm the correct chain was deployed after a renewal, and to check that a CDN or load balancer is serving the certificate you expect. Anyone migrating hosts or rotating certificates benefits from a fast before-and-after confirmation.

A smart practice is to check well ahead of the expiration date and to automate renewals where possible, since most outages come from forgotten manual renewals rather than technical faults. If the tool reports a hostname mismatch, confirm the SAN list includes every name users access, including the bare domain and www variants. To understand the broader response context around the secure connection, pair this with an HTTP Header Analyzer to review security headers like HSTS that complement TLS.