SSL Certificate Decoder Guide
An SSL/TLS certificate is a digital document that binds a public key to an entity's identity (like a website domain). These certificates are typically formatted in Base64-encoded ASCII blocks known as PEM format. The SSL Certificate Decoder helps you parse these opaque blocks into human-readable information to verify expiration dates, identify issuers, and ensure correct domains are covered.
⚙️ Key Features
- Instantly decodes PEM encoded X.509 certificates.
- Displays critical information including Subject, Issuer, and Validity periods.
- Alerts you automatically if a certificate is expired or expiring soon.
- Extracts and lists Subject Alternative Names (SANs) and Key Usages.
📖 How to Use
- Paste your PEM encoded certificate into the input area.
- Alternatively, drag and drop a .pem or .crt file, or use the Upload button.
- Review the decoded details in the output panel.
- Use the 'Copy Summary' button to quickly grab the most important details for reports.
All certificate decoding happens purely client-side using JavaScript. No certificate contents or metadata are transmitted over the network.
Frequently Asked Questions (FAQ)
What is a PEM certificate?
PEM (Privacy Enhanced Mail) is the most common format for X.509 certificates, CSRs, and cryptographic keys. A PEM file is essentially a Base64-encoded block of data enclosed between '-----BEGIN CERTIFICATE-----' and '-----END CERTIFICATE-----' headers.
What are Subject Alternative Names (SANs)?
The SAN extension allows multiple domain names to be protected by a single SSL certificate. This is the modern standard for identifying which hostnames a certificate is valid for, superseding the Common Name (CN) field.
Is my certificate sent to a server for decoding?
No. All parsing and decoding is performed locally in your browser. Your public certificate data never leaves your device.