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SSL Certificate Checker
Issuer, validity window and days until expiry.
About the SSL Certificate Checker
Connects to the host, reads the certificate chain and reports the issuer, the validity window, the covered hostnames and whether the chain resolves to a trusted root.
The two failures that actually break sites are expiry and hostname mismatch. A certificate covering example.com but not www.example.com throws a full-page browser warning on half your traffic, and nobody clicks through those.
The other thing to check is the intermediate certificate. A chain that is valid in your browser because it happens to have the intermediate cached may fail for other clients and for crawlers. If the chain here shows as incomplete, fix the server configuration rather than assuming it works because it worked for you.
Common questions
Why does my certificate work in my browser but fail here?
Your browser may have cached an intermediate certificate from an earlier visit, masking an incomplete chain on the server. Other browsers, crawlers and API clients without that cache will see the failure this tool reports.
What happens if my certificate covers example.com but not www.example.com?
Visitors on the missing variant see a full-page browser security warning, which stops nearly all of them from continuing — this is one of the most common and most damaging SSL misconfigurations.
How soon before expiry should I renew?
Most automated systems like Let's Encrypt renew around 30 days before expiry. If you're managing certificates manually, check at least two weeks ahead to leave time to fix any issue.