What information can I extract from an X.509 certificate?

An X.509 certificate contains the subject (owner), issuer (CA), validity period, Subject Alternative Names (SANs), public key, signature algorithm, serial number, and extensions such as Key Usage and Extended Key Usage.

What is the difference between PEM and DER format?

PEM is a Base64-encoded certificate wrapped in -----BEGIN CERTIFICATE----- headers, commonly used in files. DER is the raw binary form. This tool accepts both formats.

X.509 Certificate Inspector — Parse, Decode & Analyze SSL Certs

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