SSL / X.509 Certificate Decoder
Decode PEM-encoded X.509 SSL certificates (.crt, .pem) to view issuer, validity dates, subject, and fingerprints.
| Subject Domain (CN) | |
| Issuer (CA Authority) | |
| Validity Period | |
| Days Remaining | |
| Serial Number & Algorithm |
1 How to Use the SSL / X.509 Certificate Decoder
Paste your PEM certificate beginning with '-----BEGIN CERTIFICATE-----'.
The parser automatically decodes the X.509 certificate hierarchy.
Inspect Subject, Issuer (e.g. Let's Encrypt, DigiCert), Not Before, Not After, and days left.
Verify SHA-256 fingerprint and serial number.
2 Technical Specifications
| Specification | Details & Capabilities |
|---|---|
| Standard | ITU-T X.509 v3 / RFC 5280 |
| Fields Parsed | Subject, Issuer, Validity Dates, Serial Number, Signature Algorithm, Fingerprint |
| Format | PEM (Base64-encoded DER) |
| Execution | Client-Side Parser |
Trust and Privacy
100% Client-Side Privacy Guarantee
All calculations run directly in your local browser memory. Zero data is ever transmitted, logged, or stored on remote servers.
4 Frequently Asked Questions
Q. What happens when an SSL certificate expires?
Web browsers show a full-page security warning ('Your connection is not private', ERR_CERT_DATE_INVALID) and block visitors from accessing your website.
Q. What is the certificate fingerprint?
The fingerprint is a unique cryptographic hash (typically SHA-256) of the entire certificate binary, used to verify that the certificate matches the intended certificate authority.