X.509 Certificate Decoder
Paste a PEM certificate to parse the subject, issuer, validity, Subject Alternative Names, serial, public key and signature algorithm. Parsed locally · never paste a private key.
PEM certificate
Decoded certificate
Paste a PEM certificate and click Decode.
Related tools
How to use
1
Paste the PEM
Include the BEGIN/END CERTIFICATE lines, or just the base64 body.
2
Decode
Subject, issuer, dates, SAN and key details are extracted locally.
3
Check validity
Expired or not-yet-valid certificates are flagged.
Frequently Asked Questions
A base64 text encoding of a DER X.509 certificate, wrapped in BEGIN/END CERTIFICATE lines · the most common way certificates are shared as text.
The SAN extension lists every identity a certificate covers · DNS names, IPs, emails, URIs. Browsers validate the hostname against the SAN, not the Common Name.
No · it is parsed entirely in your browser. Still, never paste a private key into any online tool. This decoder is for public certificates only.
No, and it should not. It decodes X.509 certificates only. Keep private keys on trusted, offline systems.
A free tool from mlab, the intelligence platform for IOC, domain and file analysis. Rolling this out across a team? Talk to us.