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Certificate Decoder

Decode and inspect SSL/TLS X.509 certificates with detailed field breakdown and ASN.1 structure

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About This Tool

Certificate Decoder parses PEM-encoded SSL/TLS X.509 certificates directly in your browser, displaying subject, issuer, validity dates, SANs, key usage, extended key usage, basic constraints, SHA-256 and SHA-1 fingerprints, and the raw ASN.1 structure. No data is sent to any server.

Key Features

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Use Cases

ssl tls x509 certificate pem

Frequently Asked Questions

What is the Certificate Decoder?

The Certificate Decoder is an online tool that parses PEM-encoded SSL/TLS X.509 certificates and displays subject, issuer, validity dates, SANs, key usage, fingerprints, and raw ASN.1 structure β€” all locally in your browser.

What certificate formats are supported?

The tool supports PEM-encoded X.509 certificates, which are the most common format used for SSL/TLS. Simply paste the certificate including the BEGIN CERTIFICATE and END CERTIFICATE headers.

Does the Certificate Decoder send my certificate to a server?

No. All decoding and parsing happens entirely in your browser using JavaScript. Your certificate data is never transmitted to any external server, ensuring complete privacy.

What information can I see after decoding a certificate?

You can view the subject and issuer details, serial number, version, signature algorithm, public key algorithm, validity period with expiry countdown, SANs, key usage, extended key usage, basic constraints, SHA-256 and SHA-1 fingerprints, and the raw ASN.1 structure.

Can I copy the decoded certificate information?

Yes. After decoding, a Copy Report button appears that copies a complete text report of all decoded certificate fields to your clipboard.