SSL Certificate Decoder
Paste a PEM-encoded SSL certificate and inspect its issuer, subject, validity, SANs, and fingerprint.
How to use the SSL Certificate Decoder
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Paste a PEM certificate (the block between -----BEGIN CERTIFICATE----- and -----END CERTIFICATE-----).
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Review the decoded fields.
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Check validity dates and SANs.
What is an SSL/TLS certificate?
An X.509 certificate binds a public key to a domain name and organization, signed by a trusted Certificate Authority. Browsers verify this chain to establish HTTPS. This decoder unpacks the ASN.1 structure and shows every field in readable form — common name, organization, validity window, SANs, key algorithm, and SHA-256 fingerprint. Decoding happens in your browser; the certificate is never sent anywhere.
Key features
- Decodes PEM (base64-encoded) X.509 certificates
- Shows Subject, Issuer, Validity, SANs, and Key Info
- Flags expired or soon-to-expire certificates
- Fully local — the certificate never leaves your browser
Frequently asked questions
Is my certificate uploaded anywhere?
No. Decoding runs entirely in your browser using the Web Crypto API. Your certificate never leaves your device.
What format does the certificate need to be in?
PEM format — the Base64 block wrapped with BEGIN/END CERTIFICATE lines. DER binary is not supported.
Does it verify if the certificate is trusted?
No — this is a decoder, not a validator. It shows what's in the certificate but does not check the CA chain or revocation status.