Paste a PEM certificate, certificate chain or CSR (or a bare base64/hex DER blob), or choose a file. Everything is decoded locally in your browser; nothing is uploaded or stored, and the page has no analytics.
Paste the text between BEGIN CERTIFICATE and END CERTIFICATE above and press Decode. You get the subject, issuer, SANs, validity dates, key type and size, and SHA-1/SHA-256 fingerprints.
Decoding happens in JavaScript in your browser. Nothing is sent to a server. Certificates are public data anyway, but never paste private keys into any website.
Yes: CSRs, bundles with several certificates, and DER files are all supported. It also converts between PEM and DER.