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    PEM Certificate Decoder

    Decode and inspect X.509 certificates — subject, issuer, SANs, key info, extensions & security analysis. 100% client-side.

    🔒 Client-Side Only
    X.509 v3
    RSA & EC

    Paste PEM Certificate

    Paste a PEM-encoded certificate (starts with -----BEGIN CERTIFICATE-----). Nothing leaves your browser.

    How It Works

    This tool parses X.509 certificates entirely in your browser using a pure JavaScript ASN.1 DER parser. No data is sent to any server.

    • Decodes ASN.1 DER structure from PEM base64 encoding
    • Extracts subject, issuer, validity, public key info, and extensions
    • Parses Subject Alternative Names (DNS, IP, URI, Email)
    • Analyzes key strength, signature algorithm, and expiry
    • Computes SHA-256 fingerprint using Web Crypto API

    Tip: To get a certificate from a website, run: openssl s_client -connect example.com:443 -servername example.com </dev/null 2>/dev/null | openssl x509