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Certificate Decoder

Paste a PEM or base64 certificate, decode subject, issuer, SANs, dates.

Why this exists

The TLS checker reads a live host, but plenty of certs arrive as a .cer or PEM blob, code-signing certs, client certs, a ThreatLocker cert policy. This decodes one offline, in your browser, without standing up a server to serve it.

How to use
  1. Paste a certificate in PEM (-----BEGIN CERTIFICATE-----) or raw base64 form.
  2. See subject, issuer, validity dates, SANs, serial, key type, and signature algorithm.
  3. Everything runs locally, the certificate never leaves your browser.

Parsed locally in your browser, the certificate is never uploaded.

Paste an X.509 certificate above, PEM (-----BEGIN CERTIFICATE-----) or raw base64 DER. You'll get subject, issuer, validity, SANs, key + signature info and fingerprints.