How to Use the SSL Certificate Decoder

Decoding a Certificate

Paste your PEM-encoded SSL/TLS certificate into the input field
Click "Decode Certificate"
View all certificate details including subject, issuer, validity, and fingerprints
Check expiration status and days remaining

Getting a Certificate

You can obtain a certificate from a website using OpenSSL or your browser:

echo | openssl s_client -servername example.com -connect example.com:443 2>/dev/null | openssl x509 -text

What is an SSL/TLS Certificate?

SSL/TLS certificates are digital certificates that authenticate the identity of websites and enable encrypted connections. They contain information about the certificate holder, the issuing Certificate Authority (CA), validity dates, and a public key. X.509 is the standard format for these certificates, used across HTTPS, email encryption, and code signing.

Certificate Information Explained

Subject & Issuer

Subject: The entity (website, organization, person) the certificate is issued to
Issuer: The Certificate Authority that signed and issued the certificate
Common Name (CN): Usually the domain name for SSL certificates

Validity Period

Not Before: Certificate is not valid before this date
Not After: Certificate expires after this date
Days Remaining: How many days until expiration

Fingerprints

SHA-1 and SHA-256 fingerprints are unique hashes of the certificate. They're used to verify certificate authenticity and are often displayed in browsers when examining security details.

Common Use Cases

For DevOps Engineers

Verify certificate expiration dates before they cause outages
Check Subject Alternative Names (SAN) for multi-domain certificates
Validate certificate chains and issuing CAs
Debug SSL/TLS connection issues

For Security Professionals

Analyze certificate properties and extensions
Verify fingerprints for certificate pinning
Check key algorithms and signature methods
Audit certificate configurations

For Web Developers

Troubleshoot HTTPS setup issues
Verify SSL certificate installation
Check certificate details for API integrations
Monitor certificate expiration for renewals

Features

100% Client-Side - All decoding happens in your browser using JavaScript
Complete Information - View all certificate fields including extensions
Expiration Alerts - Instant notification if certificate is expired or expiring soon
Fingerprint Calculation - Automatic SHA-1 and SHA-256 fingerprint generation
Privacy First - Your certificates never leave your browser
PEM Format Support - Standard X.509 PEM-encoded certificates

Frequently Asked Questions

Is my certificate data safe?

Yes! All certificate decoding happens entirely in your browser using JavaScript. Your certificate data never leaves your device and is never sent to any server. We don't log, store, or transmit any data.

What certificate format is supported?

This tool supports PEM-encoded X.509 certificates (the most common format). These start with -----BEGIN CERTIFICATE----- and end with -----END CERTIFICATE-----.

Can I decode certificate chains?

Currently, this tool decodes one certificate at a time. If you have a certificate chain, paste each certificate separately to view its details.

What are Subject Alternative Names (SAN)?

SANs allow a single certificate to secure multiple domain names. Modern certificates use SANs instead of (or in addition to) the Common Name field to specify which domains the certificate is valid for.

Why is fingerprint verification important?

Fingerprints provide a unique identifier for a certificate. They're used in certificate pinning to ensure you're connecting to the expected server and to detect man-in-the-middle attacks.