How to Check If Your SSL Certificate Is Properly Installed

Installing an SSL certificate is only half the battle — you need to verify it's correctly installed, the chain is complete, and there are no configuration errors. Here's a systematic checklist.

1. Decode the Certificate You Received

Before installing, paste the certificate PEM into the SSL Certificate Decoder and verify:

• The Subject Alternative Names match the domains you need
• The expiry date is correct
• The issuer matches the CA you ordered from
• The fingerprint matches the CA's confirmation

2. Check the Live Connection with OpenSSL

openssl s_client -connect yourdomain.com:443 -servername yourdomain.com

Look for:

• Verify return code: 0 (ok) — the chain validates successfully
• The certificate chain depth — intermediates should be present
• The server certificate subject and expiry

3. Verify the Full Chain

A missing intermediate causes intermediate certificate errors on some clients even if your browser works fine (because browsers cache intermediates from previous sessions). Test with openssl s_client on a fresh machine, or use -verify_return_error to see strict chain validation.

To check the chain explicitly:

openssl s_client -connect yourdomain.com:443 -showcerts </dev/null 2>/dev/null | \
  grep "subject\|issuer"

4. Check for Mixed Content

A valid certificate doesn't guarantee a clean HTTPS page. Mixed content warnings occur when an HTTPS page loads resources (images, scripts, CSS) over HTTP. Check your browser's developer console for mixed content warnings after installation.

5. Verify the Key Matches the Certificate

A mismatch between the private key and certificate causes the web server to fail to start. Verify with OpenSSL:

# MD5 hashes must match
openssl x509 -noout -modulus -in cert.pem | openssl md5
openssl rsa -noout -modulus -in key.pem | openssl md5

6. Test from Multiple Locations

Use services like SSL Labs' Server Test (ssllabs.com) or a synthetic monitoring service to verify the certificate and TLS configuration from external vantage points — catching issues that local testing might miss.