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X.509 Certificate Decoder

An offline X.509 parser. Paste any standard SSL/TLS PEM certificate to extract human-readable metadata like the Issuer CA, Expiration Limits, Thumbprints, and Subject Alternative Names (SANs) completely offline.

What is the WebCrypto ASN.1 Inspector?

Public Key Infrastructure (PKI) Certificates are normally encoded in X.509 standard format, serialized in Abstract Syntax Notation One (ASN.1), and wrapped in Base64 (PEM format).

How it Works under the hood

When you paste the PEM payload, the javascript engine reverse-compiles the Base64 sequence back into binary ASN.1. It traverses the tree structure strictly within the browser memory to extract human readable attributes natively bypassying any network API validations.

SysAdmin & Security Use Cases

  • »Inspecting a deployed certificate chain locally to debug untrusted errors
  • »Verifying precisely which subdomains (SANs) a wildcard cert covers
  • »Validating expiry dates exactly down to the GMT second before installation
  • »Extracting SHA1 / SHA256 fingerprints to pin certificates in API clients