Certificate Decoder
Decode and inspect X.509 SSL/TLS certificates. View subject, issuer, validity period, SANs, and fingerprint.
About This Tool
X.509 Decoding
Parse PEM-encoded X.509 certificates and extract subject, issuer, key information, and extensions.
Validity Check
Instantly see if a certificate is currently valid, expired, or self-signed with days remaining.
SAN Inspection
View all Subject Alternative Names including DNS names and IP addresses covered by the certificate.
SHA-256 Fingerprint
Compute and display the SHA-256 thumbprint for certificate verification and pinning.
Learn More
Learn how SSL/TLS certificates work, what PEM encoding contains, and how to decode certificates to inspect subject, issuer, SANs, and validity.
What Is a Certificate Decoder
SSL/TLS certificates are the backbone of encrypted web communication. Every HTTPS connection relies on a certificate to prove a server's identity and establish a secure channel. But certificates are encoded in PEM or DER format, making their contents opaque without a decoder. A certificate decoder parses the binary structure and displays the human-readable fields like subject, issuer, validity dates, and public key details.