What an SSL/TLS certificate proves
An SSL/TLS certificate lets a website prove its identity and encrypt the connection between your browser and the server. A certificate authority (CA) issues it, vouching that the holder controls the domain. Browsers show a padlock when a valid, in-date certificate is presented by a trusted CA.
Why expiry matters
Certificates are issued for a fixed window (often 90 days to a year). If one
expires, visitors see a full-page security warning and many will leave. This
checker shows the exact valid to date and how many days remain,
so you can renew before that happens.
How this works
This tool runs on our server, which opens a TLS connection to the hostname you enter and reads the certificate it presents. We only connect to publicly reachable hosts and don't store anything. Invalid or self-signed certificates are still shown so you can diagnose the problem.