Certificate Decoder
Paste your PEM-encoded SSL/TLS certificate to instantly decode and view all fields — validity dates, subject, issuer, SANs, key info, and fingerprints.
About Certificate Decoder
The SSL Certificate Decoder is a free online tool that reads and displays the human-readable contents of an SSL/TLS certificate from its PEM-encoded text. SSL certificates contain important information in an encoded format that is not directly readable — this tool decodes and presents that information clearly.
Server administrators, DevOps engineers and security professionals use certificate decoders to verify certificate details before deployment or troubleshoot SSL configuration issues.
How to Decode an SSL Certificate
- Copy your PEM-encoded certificate (the text block starting with -----BEGIN CERTIFICATE-----)
- Paste it into the input field
- Click Decode Certificate
- View all decoded certificate details
Information Revealed by Decoding
- Common Name (CN) — the primary domain the certificate is issued for
- Subject Alternative Names (SANs) — additional domains/subdomains covered
- Issuer — the Certificate Authority that issued it (DigiCert, Let's Encrypt, etc.)
- Validity period — issue date and expiry date
- Public key algorithm and size — RSA 2048, EC 256, etc.
- Serial number and fingerprint
Use alongside our Certificate Key Matcher to verify your certificate and private key pair correctly. Both tools are free with no login required.
Want to learn more? Read our complete guide: What is SSL and Does HTTPS Affect Google Rankings? →
Frequently Asked Questions
-----BEGIN CERTIFICATE----- and -----END CERTIFICATE----- markers. Most web servers and CAs provide certificates in PEM format.