How to check an SSL certificate, expiration date and hostname
Learn what an SSL certificate checker verifies, how expiration works, why hostname matching matters and what common certificate errors mean.
What does an SSL certificate checker verify?
An SSL certificate checker connects to a website over HTTPS and inspects the certificate presented by the server. A useful check confirms whether the certificate can be trusted, whether it matches the requested hostname and when its validity period ends.
How to check an SSL certificate expiration date
Every certificate has a validity window with a start date and an expiration date. The expiration date matters operationally because browsers normally reject an expired certificate even if the website itself is still online. The Notinexa SSL Checker calculates the number of days remaining from the certificate presented by the server.
What is hostname matching?
A valid certificate must cover the hostname being visited. For example, a certificate issued for one domain cannot automatically secure an unrelated domain. Modern certificates commonly include one or more DNS names in the certificate's Subject Alternative Name fields.
What does certificate issuer mean?
The issuer identifies the certificate authority or issuing chain responsible for the certificate. A successful browser-style verification requires more than an issuer name: the certificate chain must lead to a trusted root and the certificate must also be valid for the requested hostname and current time.
What happens when a certificate expires?
An expired certificate can cause browser security warnings and break HTTPS clients, integrations and automated requests. Certificate renewal is therefore normally automated and should complete before the expiration date rather than waiting until the final day.
SSL certificate vs TLS
The term “SSL certificate” remains common in searches and product names, but modern HTTPS connections use TLS. The certificate identifies and authenticates the server while TLS provides the encrypted connection.
Common SSL certificate errors
- Expired: the certificate validity period has ended.
- Hostname mismatch: the certificate does not cover the requested domain.
- Untrusted: the certificate chain cannot be verified against the trusted certificate store.
- Unavailable: a usable TLS certificate could not be retrieved from the server.