The checker connects to the server on port 443, reads the certificate and chain, and reports the issuer, validity dates, days to expiry, all covered hostnames (SANs), whether the name matches, whether the chain is trusted, plus the TLS protocol and cipher.
How to check an SSL certificate
- Enter the domain, for example example.com or www.example.com.
- Press Check SSL.
- Fix anything marked in red: expired, name mismatch or untrusted chain.
Common SSL problems
- Name mismatch: the certificate covers example.com but not www.example.com (or the reverse). Reissue it with both names.
- Incomplete chain: the server sends the certificate without the intermediate certificate, so some browsers and apps fail. Install the full chain (fullchain.pem).
- Expired: Let’s Encrypt certificates last 90 days; check that auto-renewal is running.
Frequently asked questions
How long are SSL certificates valid?
Public certificates are currently valid for up to 398 days, and the CA/Browser Forum has approved gradually shorter lifetimes from 2026 onwards. Let’s Encrypt issues 90-day certificates.
Updated October 2026 · Built and tested by Sharjeel Tahir · How our tools are tested