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Certificate / CSR / PEM Decoder

Decode X.509 certificates, CSRs, CRLs and any ASN.1 structure from PEM or DER.

Free, no uploads, no sign-up. Runs 100% in your browser.

How Certificate / CSR / PEM Decoder works

Certificates are parsed with PKI.js and asn1js. You see subject, issuer, validity, key type and size, every extension (SANs, key usage, policies) and SHA-1 and SHA-256 fingerprints. Unknown blocks are shown as an ASN.1 tree.

Input: PEM, CRT, CER, DER, CSR, CRL.

How to use Certificate / CSR / PEM Decoder

1. Open Certificate / CSR / PEM Decoder and paste or type your input.
2. Results update instantly as you type.
3. Tweak options such as format, indentation or algorithm.
4. Copy the output or download it as a file.

Tips

• Everything is computed locally. Safe for tokens, keys and private data.
• Use Ctrl/⌘ + K to jump between developer tools quickly.

Certificate / CSR / PEM Decoder FAQ

Are my files uploaded?

No. This tool runs entirely in your browser tab. Files are read from your disk into memory and the result is generated locally.

Is it free? Are there limits or watermarks?

Free and open source (MIT). There are no file-size caps, daily quotas, accounts or watermarks.

Does it work offline?

Yes, once the page (and any engine it needs) has loaded, it keeps working without a connection thanks to the service worker cache.

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