d4 · tools · cert decoder
Paste a PEM certificate or certificate signing request to read its subject and issuer, validity and expiry, key algorithm and size, subject alternative names, and the usage constraints. The TLS inspector fetches a live endpoint; this one decodes a PEM you already hold. Everything runs in your browser; nothing you type leaves this page.
Accepts an X.509 certificate (-----BEGIN CERTIFICATE-----) or a PKCS#10 request (-----BEGIN CERTIFICATE REQUEST-----). Encrypted or private-key blocks are not decoded.
This tool parses the DER structure of a certificate or request and reports what it contains; it does not verify the signature, check the chain, or contact any certificate authority. Validity is judged against your own device clock, so a wrong local clock will give a wrong verdict. Times are shown in UTC. Certificates and requests can be sensitive, so decoding happens entirely on your device and nothing is uploaded.