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Paste a PEM certificate to see its subject, issuer, validity dates, subject alternative names, key details, fingerprints and extensions in plain view.
Everything runs locally in your browser. Your data never leaves your device.
Accepts one or more PEM blocks (a full chain), a PKCS#10 CSR, or bare base64 or hex DER.
This tool decodes an X.509 certificate and shows every field in plain view: subject and issuer with each attribute spelled out, the validity window with a clear valid or expired verdict and the days remaining, subject alternative names, serial number, public key details, key usages, basic constraints and the SHA-256 and SHA-1 fingerprints.
Paste a single certificate, a whole chain or a PKCS#10 certificate request. A chain decodes into one card per certificate in order, so you can follow a leaf up to its root. Base64 or hex DER without the PEM armor works too, and every value has its own copy button.
Each certificate shows its subject and issuer with every attribute labeled (common name, organization, country and so on), the notBefore and notAfter dates in UTC and local time, all subject alternative names, the serial number, the X.509 version, the public key (RSA modulus size and exponent, or the EC curve), the signature algorithm, key usages, extended key usages, basic constraints and the subject and authority key identifiers. Extensions the tool has no dedicated field for are listed by name and OID, with critical ones flagged.
PKCS#10 certificate requests decode too: the requested subject, key details and requested subject alternative names, plus a check that the request's own signature verifies.
The input can hold several PEM blocks at once, so pasting a fullchain.pem just works. Private key blocks mixed into the file are ignored, never decoded. Without PEM armor the tool also accepts a certificate's raw DER as base64 or hex.
The tool reads certificates, it does not validate chains. It tells you whether a certificate is expired and what it claims about itself, but it does not verify signatures against issuers, check revocation or build a trust path.
Open source does the heavy lifting in this tool. Thank you to:
An X.509 certificate library built on the Web Crypto API.
Everything this site builds on is listed on the credits page.
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