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TLS Certificate Decoder
Paste a PEM certificate to see everything inside it, decoded locally.
Certificate
DER/ASN.1, decoded locallySubject & issuer
| Subject | |
|---|---|
| Issuer | |
| Serial number | |
| Version |
Validity
| Not before | |
|---|---|
| Not after | |
| Status |
Public key
| Algorithm | |
|---|---|
| Size |
Signature
| Algorithm |
|---|
Extensions
| Extension | Critical | Value |
|---|
Fingerprints
| SHA-256 | |
|---|---|
| SHA-1 |
A hand-written DER/ASN.1 reader scoped to what X.509 actually uses — not a general parser. Verified field-by-field against openssl x509 -text output for hand-generated EC and RSA test certificates (see tests/x509.test.ts). This decodes what's inside the certificate; it does not validate the chain, check revocation, or confirm the signature is genuine.