SSL Certificate Decoder
Paste a PEM certificate to decode its subject, issuer, SANs, validity dates, serial number, and key info — all client-side.
Use the SSL Certificate Decoder
PEM Certificate
How to get your certificate:
openssl s_client -connect example.com:443 </dev/null 2>/dev/null | openssl x509 -outform PEM
No certificate decoded yet
Paste a PEM certificate on the left and click Decode
Validity Period
Valid From
Valid To
Subject & Issuer
Subject Alternative Names
Technical Details
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Summary
The SSL Certificate Decoder parses any PEM-encoded X.509 certificate and displays its structured fields without sending data to a server. Paste the full -----BEGIN CERTIFICATE----- block and get the subject, issuer, Subject Alternative Names, validity window, days until expiry, serial number, signature algorithm, and public key details in seconds.
How it works
- Copy the PEM certificate (the -----BEGIN CERTIFICATE----- block) from your server or browser.
- Paste it into the text area on this page.
- Click "Decode Certificate" to parse the X.509 structure using the node-forge library in your browser.
- Review the decoded fields: subject, issuer, SANs, validity dates, and more.
- All parsing happens locally — your certificate data never leaves your device.
Use cases
- Verify a newly issued certificate before deploying it to production.
- Confirm the Subject Alternative Names cover all required domains.
- Check expiry dates on certificates that are approaching renewal.
- Inspect issuer chain details for troubleshooting SSL handshake errors.
- Audit certificate serial numbers for compliance records.
- Validate the signature algorithm meets current security standards (e.g., SHA-256).
- Quickly read a certificate downloaded from a vendor or partner.
Frequently Asked Questions
Last updated: 2026-06-11 · Reviewed by Nham Vu