SSL Certificate Checker

What is SSL Certificate Checker?

This SSL certificate checker opens a TLS connection to the target and reads the full certificate chain, showing the subject, issuer, validity window, and days remaining at every level, along with the negotiated TLS version and cipher suite and the reason behind any chain validation failure. Reading a certificate requires completing a handshake, so this check runs on this site's server.

How to use SSL Certificate Checker

1. 1Enter a domain name, or host:port when the service runs on a non-standard port.
2. 2Click Check to see the remaining validity and the certificate chain.
3. 3If chain validation fails, work through the reported reason; a missing intermediate certificate is by far the most common cause.
4. 4Confirm that the SAN list covers every domain you actually serve.

How do I do this in code?

Use the tool above for one-off work; for anything you repeat, move it into a script or your project.

# Show the validity dates and subject
echo | openssl s_client -servername example.com -connect example.com:443 2>/dev/null \
  | openssl x509 -noout -dates -subject

# Check whether the certificate chain is complete
openssl s_client -showcerts -servername example.com -connect example.com:443 < /dev/null

Common errors and how to fix them

Frequently asked questions