Your site can use HTTPS and still be misconfigured
The padlock in the address bar means a certificate validated and a connection was encrypted. It does not mean the protocol version is current, the cipher suites are strong, the chain is complete, or the certificate will still be valid next month. Those are separate facts, and they are the ones this check reads.
What this check reads
Protocol versions, cipher suites, forward secrecy, the certificate and its chain. It completes handshakes and reads what the server offers. It sends no application data and attempts no known TLS attack.
- Which TLS versions the server accepts, including the deprecated ones
- Whether any offered cipher suite is in a broken family
- Whether forward secrecy is available
- Certificate validity dates, hostname coverage and chain trust
The most common real finding
A certificate that expires in under three weeks with no working renewal. It is not exotic, it is not interesting, and it takes a site offline for every visitor the moment it happens. Renewals fail silently far more often than they fail loudly, so the useful check is not whether renewal is scheduled but whether the served certificate date is actually moving.