Free SSL tool

SSL Decoder

Paste any PEM-format SSL certificate and instantly decode every field: issuer, subject, Subject Alternative Names (SANs), validity period, public key strength, signature algorithm, and certificate extensions.

How to decode an SSL certificate or CSR

Paste the PEM text — Copy the full PEM block — either a certificate (-----BEGIN CERTIFICATE-----) or a CSR (-----BEGIN CERTIFICATE REQUEST-----) — and paste it into the field.
Click "Decode" — The tool parses the ASN.1 structure and extracts all readable fields.
Review the output — You'll see the subject (Common Name, organization, country), issuer, validity dates, SANs (Subject Alternative Names), public key details, and signature algorithm.
Use the data — Verify the domain names covered, check expiry, or confirm the organization details match what you ordered.

Frequently asked questions

What is PEM format?

PEM (Privacy Enhanced Mail) is a Base64-encoded text format used for certificates, CSRs and keys. It begins with a -----BEGIN ...----- header and ends with a -----END ...----- footer.

What is a Subject Alternative Name (SAN)?

SANs are additional domain names covered by a single certificate. Modern SSL certificates use SANs instead of the older wildcard or multi-domain approach. Check this field to see all domains the certificate is valid for.

Can I decode a CSR before submitting it?

Yes, and you should. Decoding lets you verify that the Common Name, organization name and key size are correct before sending it to the CA.

Is the decoding done server-side?

No. The decoder runs entirely in your browser using JavaScript. The certificate or CSR data you paste is not sent to any external server.