How to Decode an SSL Certificate Online
Need to inspect an SSL certificate without installing command-line tools? The SSL Certificate Decoder lets you decode a certificate online and view the fields that matter for troubleshooting, security reviews, and hostname checks.
How to decode an SSL certificate online
- Open the online SSL certificate decoder.
- Paste the complete PEM certificate into the text box. Include the lines
-----BEGIN CERTIFICATE-----and-----END CERTIFICATE-----. - If you have a certificate file instead, use the upload option and select the certificate from your device. Common formats include
.pem,.crt, and.cerwhen they contain a PEM-encoded certificate. - Start the decode process and review the parsed certificate details.
What the decoded fields mean
Issuer
The Issuer identifies the certificate authority that signed the certificate. This helps you confirm which CA issued it and investigate trust-chain or renewal issues.
Subject
The Subject describes the certificate holder, including the common name and organization details when they are present. It provides the certificate's legacy identity information.
Subject Alternative Name (SAN)
SAN lists the hostnames and other identities protected by the certificate. Modern browsers rely primarily on SAN, so check that the exact domain you use appears there.
Validity period
Review the Not Before and Not After dates to see when the certificate becomes valid and when it expires. An expired certificate or a device with an incorrect clock can cause TLS warnings.
Serial Number
The Serial Number is a unique identifier assigned by the issuer. It is useful when matching a certificate to an inventory record, renewal, or revocation notice.
Fingerprint
The Fingerprint is a hash of the certificate, commonly shown as SHA-256. Compare it with a trusted copy when verifying that the certificate is the one you intended to install.
PEM paste or file upload?
Use PEM paste when the certificate is already available as text in a configuration file, terminal output, or email. Use upload when you have the original certificate file. The decoder reads the certificate itself; it does not require the private key, and you should never upload a private key.
Check the certificate before deployment
Before installing a certificate, confirm the SAN contains every required hostname, the validity period is appropriate, and the Issuer is expected. Save the Serial Number and SHA-256 Fingerprint if you need to document the deployment or compare certificates across servers.
For a quick check, go straight to the SSL Certificate Decoder homepage, paste the PEM block or upload the certificate, and inspect the decoded results.
