Paste a certificate in PEM, a whole chain, or DER as base64/hex. Everything is parsed locally: identity, validity, key and signature algorithms, extensions and fingerprint — with plain-English notes on algorithm health.
100% local — everything runs in your browser, nothing is sent to any server
Your certificate never leaves this page. The input is split into PEM blocks (or decoded from base64/hex DER), and each block is parsed with an ASN.1 parser compiled into the page itself — subject, validity, key parameters and extensions are read directly from the DER structure. The SHA-256 fingerprint is computed in JavaScript in your browser as well, so no bytes are uploaded anywhere. Assessment notes are rule-based: signature hashes are checked against what modern clients accept, key algorithms against the NIST IR 8547 post-quantum timeline, and lifetimes against the CA/Browser Forum schedule.