What information does it show from the certificate?

Subject, issuer, and validity period (not-before and not-after dates), the key details most useful for a quick certificate check.

Does it work on both certificates and CSRs?

Yes, it decodes both PEM-encoded X.509 certificates and certificate signing requests.

Is my certificate data uploaded anywhere to decode it?

No, decoding happens locally in your browser — the certificate content isn't sent anywhere.

Does Certificate/CSR Decoder upload my files to a server?

No. Certificate/CSR Decoder runs entirely in your browser using on-device processing, your files never leave your device.

Certificate/CSR Decoder

Decode a PEM X.509 certificate or CSR to view its subject, issuer and validity.

Runs in your browser

PEM certificate or CSR

Decodes common X.509 certificate and CSR fields locally from a from-scratch ASN.1/DER parser, no data leaves your browser.

About this tool

A PEM-encoded X.509 certificate or CSR is a Base64-encoded block that's completely unreadable as-is, and decoding it to check the subject, issuer and validity dates normally means using command-line tools like openssl. This tool decodes a PEM certificate or CSR to show its subject, issuer and validity directly in the browser, giving you a readable summary without needing command-line tools installed.

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