Certificate & CSR Decoder
Paste any X.509 certificate (PEM/DER) or PKCS#10 CSR and decode everything: subject, issuer, validity & expiry, SANs, key usage, extensions, public key, and fingerprints. Auto-detects the type.
Everything is decoded locally in your browser — the certificate or CSR you paste never leaves this page. This tool does not validate CA policy, the certificate chain of trust, or possession of the matching private key.