X.509 Certificate Parser
Parse PEM and DER-encoded X.509 certificates. View all fields: subject, issuer, validity, SANs, extensions, fingerprints, and public key details. All in-browser using the Forge library.
Supported formats: PEM (Base64 with BEGIN/END markers) and DER (hex bytes). X.509 v1/v3 certificates. Extensions include Subject Alternative Name, Key Usage, Extended Key Usage, Basic Constraints, CRL Distribution Points, and more.
How to Use
From browser: Click the padlock icon in the address bar > Connection is secure > Certificate is valid > Export (or Details > Copy to file). Paste the PEM text here.
From OpenSSL: Run openssl s_client -connect example.com:443 -showcerts and copy the certificate block.
From a file: Open any .pem or .crt file in a text editor, copy the content.
Example Use Cases
- Debug TLS issues — Quickly check certificate expiry, SAN mismatches, or chain problems
- Verify certificate details — Confirm the correct subject, issuer, and extensions before deploying
- Security audits — Check key sizes, signature algorithms, and validity windows
- Development testing — Inspect self-signed certificates during local development