What is SSL/TLS?
SSL and TLS are the protocols that encrypt traffic between a browser and a server — TLS is the modern, still-used version; "SSL" stuck around as the common name. The certificate itself is issued by a certificate authority (CA) and proves the server is who it claims to be, which is what puts the padlock icon next to a URL in a browser.
What does an SSL/TLS check verify?
An SSL checker connects to a host on the given port, retrieves its certificate chain, and verifies the details that determine whether visitors' browsers will trust the connection: whether the certificate matches the hostname, whether it's signed by a publicly trusted certificate authority (rather than self-signed), and how many days remain before it expires.
Why certificate expiry matters
An expired certificate breaks HTTPS for every visitor — browsers block the page outright rather than showing a warning. Checking days-remaining regularly (or watching for the warning this tool surfaces once a certificate is within 30 days of expiry) avoids that kind of outage.
Checks happen live against the host you enter and aren't stored. See our privacy page for details.