SSL Certificate Checker
Inspect the TLS certificate for any domain: whether it's currently valid, how many days until it expires, the negotiated protocol and cipher, subject alternative names, and the full certificate chain up to the root. Useful for catching an expiring cert before it takes a site down, or verifying a certificate was actually reissued after a renewal.
Live checking is discontinued
ProxyChecker.dev no longer runs proxy checks, the API, MCP tools or paid plans. Nothing on this site tests a proxy anymore. The guides below still explain how proxy testing works and what to look for.
Need working proxies? These are the two providers we tested with:
Frequently asked questions
How many days before expiry should I renew a certificate?
Most automated renewal systems (like Let's Encrypt via certbot) renew 30 days before expiry by default. If you're managing certs manually, treat anything under 14 days as urgent since DNS or CA issues can delay a renewal.
What does an invalid certificate chain mean?
It usually means an intermediate certificate is missing from the server's configuration, so browsers that don't already trust that intermediate will fail the connection even though the leaf certificate itself is valid.
What's the difference between the certificate's Subject and its SANs?
The Subject (CN) historically identified the primary domain. Subject Alternative Names (SANs) list every domain the certificate actually covers, modern browsers ignore the CN entirely and only check SANs, so a cert needs the right SANs to be trusted for a given domain.
Is an expired certificate always a security problem?
It means the CA no longer vouches for the certificate's validity as of that date, which browsers treat as untrusted. It doesn't necessarily mean the private key was compromised, but it does mean visitors will see security warnings until it's renewed.