Free Online SSL Certificate Checker

1. Enter a domain such as example.com — the checker connects over TLS on port 443.
2. Press Check to open the connection and read the live certificate.
3. Confirm the certificate is valid and trusted at the top of the result.
4. Watch the days-remaining figure and renew well before it reaches zero.
5. Verify the host you use appears in the SAN list to avoid mismatch errors.

An SSL/TLS certificate is an X.509 document that binds a domain name to a public key and is signed by a certificate authority, letting browsers verify they are talking to the genuine site and encrypt the connection. Every certificate has a validity window with a not-before and not-after date, an issuer, a subject common name, and a Subject Alternative Name (SAN) list naming every hostname it covers, such as example.com and www.example.com.

We open a real TLS connection to the domain on port 443 from our server and read the live certificate, reporting whether it is trusted, who issued it, when it expires and how many days remain. A certificate that lapses triggers a full-page browser warning that blocks visitors, so the days-remaining figure is the number to watch — many teams renew at 30 days or automate renewal entirely. A mismatch between the host you visit and the SAN entries causes a security error even when the certificate itself is valid.

Server-side connection is required because browsers do not expose raw certificate details to page JavaScript.