Certificate decoder

Inspect a PEM or DER X.509 certificate or CSR — subject, issuer, validity, SANs, key size, and fingerprint.

Decoded in this browser. Nothing is sent anywhere.

PEM or DER up to 2 MiB. Shows the fields written in the certificate — signature validity is not checked.

How to use

  1. Paste PEM text or drop a .crt/.cer/.der/.csr file.
  2. Read the parsed fields.
  3. Copy the summary if needed.

What it supports

X.509 certificates and PKCS#10 CSRs up to 2 MiB. Shows validity dates, subject/issuer, SANs, signature algorithm, public-key size, and SHA-256 fingerprint. Chain verification, revocation, and trust checks are out of scope — use openssl or your CA tooling for those.

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