Free tool
Who issued your certificate, when it expires, which names it covers, and whether the chain of trust behind it is complete.
No account, no card, no limit on how often you run it.
An incomplete chain is the failure worth knowing about. The site works in your browser because your machine already has the intermediate certificate cached, and fails for a visitor whose machine does not. Testing it yourself will not reveal it.
It shows where things stand today, and forgets you were here the moment you close the tab. Every free checker works this way, including the well-known ones.
Watching the same domain and keeping the answers is the paid product. It starts at $15 a month and the record begins the day you do.
One check covering registration, certificate, mail, subdomains and hosting.