SSL checker

Check an SSL certificate.

Free SSL checker: see whether a certificate is trusted, valid for the hostname and when it expires, with issuer, chain, TLS version and cipher. No signup.

Get warned before it expires

What the checker looks at

Trust chain : Whether the chain the server sends leads to a root certificate that browsers trust. A missing intermediate is the most common cause of errors on some devices only.
Hostname : Whether the certificate covers the exact name you entered, including wildcard rules: *.example.com covers www.example.com but not example.com itself.
Expiry : How many days remain. Knowing 30 days ahead leaves time to renew by hand when the automation fails.
Connection : The TLS version and cipher the server negotiated with us. TLS 1.2 and 1.3 are current; older versions should be switched off.

Frequently asked questions

What does the SSL checker test?

It opens a TLS connection to the host on port 443, reads the certificate and checks whether a browser would trust the chain, whether the certificate covers the hostname and how many days remain before it expires.

Why is a certificate shown as not trusted?

Usually the server sends an incomplete chain, the certificate is self-signed or expired, or it was issued for a different name. The result shows the reason the verification failed.

How do I get warned before a certificate expires?

Create a free m0nitor account and add an SSL monitor. m0nitor checks the certificate every day and alerts you by email, Slack, Teams or other channels before it runs out.

Is the result cached?

Yes, for five minutes per host, so repeated checks do not load the server. Only the TLS handshake takes place, no page is requested.