Certificate Decoder
Decode X.509 SSL/TLS certificates in PEM format. All processing is done in your browser for maximum security and privacy.
Decoded Certificate
Subject
Issuer
Serial Number
—
Version
—
Signature Algorithm
—
Not Before
—
Not After
—
Validity
—
Public Key
Algorithm: —
Key Size: —
Subject Alternative Names (SANs)
No SANs found
Fingerprints
SHA-256: —
How to Use Certificate Decoder
Paste Certificate
Copy your PEM-encoded certificate including the BEGIN/END headers and paste it into the input field
Auto Decode
The tool automatically parses the ASN.1/DER structure and extracts all certificate fields
Inspect Details
View subject, issuer, validity dates, SANs, public key info, and SHA-256 fingerprint
What is X.509?
X.509 is an ITU-T standard for defining the format of public key certificates. An X.509 certificate binds an identity (subject) to a public key and is signed by a Certificate Authority (CA). SSL/TLS certificates used for HTTPS websites are the most common application of X.509 certificates.
SSL/TLS Certificates
X.509 certificates are the foundation of HTTPS, verifying server identity and enabling encrypted communication
Public Key Infrastructure
X.509 defines the format for public key certificates used in PKI to bind identities to cryptographic keys
ASN.1/DER Encoding
Certificates use ASN.1 Distinguished Encoding Rules (DER) for their binary structure, wrapped in PEM Base64 for text transport
Frequently Asked Questions
The tool supports PEM-encoded certificates (-----BEGIN CERTIFICATE-----). DER and P7B formats are not currently supported.
The tool decodes and displays certificate details but does not verify the chain of trust against root CAs.
Currently only X.509 certificates are supported. CSR decoding may be added in a future update.