Free to use, no account
X.509 Certificate Decoder
Inspect an X.509 certificate on this device. Paste a PEM/base64 certificate or choose a PEM, CER, CRT or DER file to read its subject, issuer, validity dates, alternative names and SHA-256 fingerprint.
How do I decode an X.509 certificate?
Paste one PEM certificate or base64-encoded DER, or select a local PEM, CER, CRT or DER file. The decoder displays certificate fields and a SHA-256 fingerprint in your browser.
Frequently asked questions
How do I decode an X.509 certificate?
Paste one PEM certificate or base64-encoded DER, or select a local PEM, CER, CRT or DER file. The decoder displays certificate fields and a SHA-256 fingerprint in your browser.
Is my certificate uploaded?
No. The selected certificate is read and decoded in this browser. It is not sent to a server. Files are limited to 1 MiB.
Does decoding prove that a certificate is trusted?
No. This tool reads certificate fields only. It does not validate signatures, issuer chains, hostnames, revocation status or browser trust.
Can I decode a DER certificate?
Yes. Choose a local DER file. You can also paste its base64-encoded DER representation.
What does the SHA-256 fingerprint identify?
It is a digest of the certificate file bytes, useful for comparing copies. It is not a trust or safety verdict.