X.509 Certificate Decoder
Options
Status
Idle
Bytes
0
Certificate details
Subject
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Issuer
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Serial number
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Version
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Expired
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Valid from
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Valid to
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Public key algorithm
—
Public key bits
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SHA-1 fingerprint
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SHA-256 fingerprint
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Subject alternative names
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Key usage
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Extended key usage
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Basic constraints
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About X.509 Certificate Decoder
This tool decodes X.509 certificates from PEM, Base64 DER, or hex DER and shows the most useful certificate metadata in a readable format.
Use it to inspect certificate subject, issuer, validity dates, fingerprints, SAN entries, key usage, and public key information without sending data to external services.
How to use it
- Paste an X.509 certificate in PEM, Base64 DER, or hex DER format.
- Choose the matching input format.
- Click Decode certificate.
- Review the decoded summary, normalized PEM, Base64 DER, and hex DER outputs.
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FAQ
Does this tool support PEM certificates?
Yes. You can paste a full PEM certificate block and decode it directly.
Can I inspect SAN entries and fingerprints?
Yes. The decoder shows subject alternative names and SHA fingerprints when available.