SSL Error Message Decoder
Explain browser SSL errors like ERR_CERT_COMMON_NAME_INVALID.
Codes the browser shows with the “Your connection is not private” warning — like ERR_CERT_COMMON_NAME_INVALID, ERR_CERT_AUTHORITY_INVALID or SEC_ERROR_UNKNOWN_ISSUER — point to SSL/TLS certificate problems. Enter the code and this tool explains what's wrong and how to fix it.
Operators get cause-specific fixes; visitors quickly learn why the warning appears.
Cause: The domain in the certificate (CN/SAN) doesn't match the one you visited. Common with www mismatches, wrong virtual hosts, or shared certs.
Fix: Reissue so all hostnames (apex and www) are in the certificate SAN, or bind the correct certificate to the host.
Top cause: missing intermediate certificate
If desktop browsers are fine but some devices/apps show “untrusted issuer,” the server likely has only the leaf certificate instead of the full chain. Install the intermediate certificates too.
If you're the visitor
When only one PC errors, its clock is often wrong, or antivirus/proxy is intercepting HTTPS.