Decode X.509 Certificate PEM — Expiry & Fingerprint
Decode PEM or DER X.509 certificates: subject, issuer, SANs, expiry, fingerprints. Multi-PEM supported. Not a trust store or TLS verifier.
Developer notes
• Order: private key only → error; CERT blocks → decoded; else try DER/base64. • CERT + PRIVATE KEY → certs decoded + warning (key ignored). • Load sample pastes a demo CA (#0) + leaf (#1) — both JSON summaries appear in output order. • Fingerprint = digest of full certificate DER. • No chain / trust-root validation. • 512 KB limit.
Options
When teams pick this route
• Check leaf PEM expiry before deploy. • Compare SHA-256 fingerprints with a ticket. • Read SANs from a staging certificate.
Worked examples
Leaf PEM → JSON summary
Before
After (summary)
Two PEM blocks → sequential JSON summaries
Before
After (summary)
Related security tools
Convert PEM public keys: pem-jwk-converter. Inspect JWKS: inspect-jwks. Hub: security tools.
Decode certificate FAQ
Local PEM / X.509
Does this tool validate the TLS chain / trust roots?
No. This tool decodes fields; it does not validate the chain against trust roots and does not prove TLS trustworthiness.
When should I use jwt-decode?
jwt-decode is for JWT tokens. For PEM certificates use this tool; for JWK/JWKS use inspect-jwks.
What about private keys?
A private key alone is rejected. Mixed with CERT blocks, certificates are decoded and the key is ignored (never shown).
Multiple PEM blocks in one paste?
Each certificate is decoded in paste order. The output shows one pretty-printed JSON summary per certificate, separated by a blank line — not a single JSON array or document. Wrap the blocks in an array yourself if you need one parseable file.
Size limit?
512 KB per paste.
Security & tokens
JWKS, X.509 certificates, and secrets scan — browser-local.
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