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Free X.509 Certificate
Decoder

Paste the issuer certificate. For a self-issued certificate, you can use the current certificate itself. Verification proves the signature against the supplied key; it does not establish OS/browser trust.

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FreeUse this tool without paying.No sign upStart with the tool right away.Clear stepsRead the tool’s own guidance.

About Free X.509 Certificate Decoder

Decode an X.509 certificate from PEM or DER into a readable security report, inspect every common extension and ASN.1 node, test hostname coverage, verify the certificate against a supplied issuer, and export machine-readable JSON — entirely in your browser.

Workspace options

  • Filter extensions
  • show critical only
  • Search ASN.1 tree
  • Hostname or IP

Available actions

  • Decode
  • Extensions
  • ASN.1 Tree
  • Verify & Hostname
  • Export
  • Guide