Security & Crypto
Certificate Decoder
Read X.509 certificates and chains: subject, SANs, validity, key, extensions and fingerprints.
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About the Certificate Decoder
Paste a PEM certificate or chain, or open a .crt, .cer or .der file, to read its subject and issuer, validity dates, Subject Alternative Names, key algorithm and size, key usage, extended key usage, and SHA-256 and SHA-1 fingerprints. Expired and soon-to-expire certificates are highlighted.
How to use it
- Paste the PEM text or open the certificate file.
- Read the decoded fields for each certificate in the chain.
- Copy the fingerprints you need.
Frequently asked questions
- How do I get a site’s certificate?
- Run openssl s_client -connect example.com:443 -showcerts and copy the BEGIN/END CERTIFICATE blocks, or export it from the browser’s padlock menu.
- Does it check that the certificate is trusted?
- No. It decodes and displays the certificate; it does not verify the signature chain or revocation.
- Is my certificate uploaded?
- No. Everything runs in your browser tab with JavaScript. Nothing you enter is uploaded, logged or stored, and the page works offline once loaded.