SSL/TLS Certificate Checker
Check the SSL/TLS certificate of any domain.
This tool opens a real TLS connection to the server and reads its certificate to show you who issued it, its validity period, how many days remain until it expires, whether it covers the queried domain, and which alternative names (SAN) it includes. Useful to avoid outages from expired certificates.
SSL certificate FAQ
It's a digital file that authenticates a website's identity and enables the encrypted HTTPS connection. It's issued by a certificate authority (CA) and has a limited validity period.
Browsers show a big security warning and block access to the site. That's why it's important to renew it before the expiry date; many services do it automatically (e.g. Let's Encrypt every 90 days).
They are the domain names the certificate covers. A single certificate can protect several domains and subdomains (for example example.com and www.example.com) by listing them in the SAN field.
It opens a real TLS connection to the server on port 443 and reads the certificate it presents, just like a browser would. It doesn't complete the encrypted connection: it only inspects the certificate.
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