X.509 Certificate Viewer

What Is an X.509 Certificate?

An X.509 certificate is a digital document that binds a public key to an identity (such as a domain name or organization). It is the foundation of TLS/SSL security on the web. Certificates contain essential information including the subject (who the certificate is issued to), issuer (who issued it, typically a Certificate Authority), validity period (not before and not after dates), serial number, signature algorithm, public key algorithm and size, and extensions like Subject Alternative Names (SANs), Key Usage, and Basic Constraints. This viewer parses PEM-encoded X.509 certificates and displays all fields in a readable format. It also computes SHA-256 and SHA-1 fingerprints. System administrators, security engineers, and developers use it to inspect certificate details, troubleshoot SSL issues, verify certificate chains, and check expiration dates.

How to Use This Tool

1. Paste a PEM certificate — Enter or paste a PEM-encoded X.509 certificate into the input area.
2. Click View Certificate — The tool parses the certificate's ASN.1 structure and extracts all fields.
3. Review the details — The output displays subject, issuer, validity dates, serial number, signature algorithm, public key information, and extensions.
4. Check fingerprints — SHA-256 and SHA-1 fingerprints are shown for certificate identification.
5. Use examples — Click the example buttons (Server, CA, Self-Signed) to see sample certificates and their parsed data.

Frequently Asked Questions