SSL Certificate Decoder — Free Online X.509 Certificate Parser
Decode and inspect X.509 SSL/TLS certificates — extract subject, issuer, validity, SANs, and fingerprints.
Jump to tool ↓Frequently Asked Questions
What Does an SSL Certificate Contain?
An SSL/TLS certificate is a cryptographic data structure encoding your server's identity and public key. It follows the X.509 standard and is typically distributed in PEM (Privacy-Enhanced Mail) format — a Base64-encoded DER structure wrapped in -----BEGIN CERTIFICATE----- headers.
The certificate contains: a Subject (the entity the cert belongs to), an Issuer (the Certificate Authority that signed it), a validity period (NotBefore / NotAfter), the server's public key, Subject Alternative Names (all domains covered), and extensions like Key Usage and Basic Constraints. The CA digitally signs all of this to prove the binding is authentic.
When you decode an SSL certificate, you can verify: which domains it covers, whether it's expired or expiring soon, which CA issued it, the key algorithm and size (RSA-2048 minimum is recommended), and the fingerprint for certificate pinning. DevDecode's SSL Decoder processes everything in your browser — your certificate PEM never leaves your machine.
Standards & References
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