Why is the output limited?

Full X.509 parsing requires an ASN.1 parser — we use a heuristic scan that finds common subject attributes (CN, O) and validity dates. For full parsing (signature, extensions, public key), use pkijs on a trusted server.

Does it verify the signature?

No — decoding shows the certificate's contents but doesn't verify the chain. Use a TLS library for verification.

What about DER format?

Not supported — only PEM (Base64-encoded DER with header/footer). Convert DER to PEM with openssl first.

Is my certificate uploaded?

No. Decoding happens entirely in your browser.

X.509 Certificate Decoder

New

Decode a PEM X.509 certificate — subject, issuer, validity.

100% private — no uploads Developer ToolsFree & unlimited Read tutorial

See how it works

Watch a quick simulation of this tool in action — no file needed.

How to use X.509 Certificate Decoder

Follow these steps — everything happens instantly in your browser.

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Step 1. Paste a PEM certificate (-----BEGIN CERTIFICATE----- … -----END CERTIFICATE-----).
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Step 2. Click Decode certificate.
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Step 3. Review the subject, issuer and validity dates.
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Step 4. Click any value to copy it.