SSL & X.509 Certificate Decoder

Paste a PEM-formatted certificate (-----BEGIN CERTIFICATE-----) to parse Subject, Issuer, SAN domains, validity period, and fingerprints 100% locally in your browser.

Certificate PEM

{{ pemSize }} bytes

Certificate Details {{ statusBadge.text }}

Subject CN{{ cert.subject.CN || '—' }}

Organization{{ cert.subject.O || '—' }}

Issuer{{ issuerLine }}

Valid From{{ formatDate(cert.validFrom) }}

Valid To{{ formatDate(cert.validTo) }} ({{ validityRemark }})

Serial Number{{ cert.serial || '—' }}

Signature Algo{{ cert.sigAlgo || '—' }}

Public Key{{ cert.publicKey || '—' }}

Versionv{{ cert.version }}

Subject Alternative Names (SANs){{ cert.sans.length }}

No Subject Alternative Name extension present in this certificate.

Fingerprints (computed over the DER certificate)

SHA-256{{ fingerprints.sha256 || '—' }}

SHA-1{{ fingerprints.sha1 || '—' }}

About SSL & X.509 Decoding

This tool walks the Base64 ASN.1 DER structure inside a standard PEM X.509 certificate — subject, issuer, validity, serial, public key and SAN extension are read directly from the bytes, and the SHA-256 / SHA-1 fingerprints are computed with the Web Crypto API. Nothing is transmitted to any server.

Security note: Parsing and fingerprinting run entirely client-side in your browser. No certificate text or key material leaves the page.