Certificate Decoder
Decode X.509 certificates to view subject, issuer, validity period, extensions, and fingerprints.
Drop a certificate file or click to upload
PEM, CRT, CER formats
X.509 Certificates - Technical Details
X.509 certificates are used for SSL/TLS to establish secure connections. They contain the public key, subject/issuer information, validity period, and extensions like Subject Alternative Names (SANs).
Command-line Alternative
# View certificate with OpenSSL\nopenssl x509 -in cert.pem -text -noout\n\n# Download website certificate\nopenssl s_client -connect example.com:443 -showcerts\n\n# Check certificate dates\nopenssl x509 -in cert.pem -dates -noout