🔐 SSL Certificate Decoder

What Can the SSL Certificate Decoder Do?

The SSL Certificate Decoder is a free online tool for parsing and viewing detailed information in SSL/TLS certificates. Whether it's a website certificate, intermediate certificate, or root certificate, simply paste the PEM format content to quickly extract key fields including Subject, Issuer, validity period, public key info, SAN extensions, and more. Pure frontend processing — certificate data is never uploaded to any server, protecting your privacy.

Core Features

• Certificate Parsing: Complete parsing of all X.509 certificate fields including version, serial number, signature algorithm, etc.
• Certificate Chain Support: Automatically identifies and displays each certificate in the chain, clearly showing the trust path
• Validity Check: Automatically compares with current time, marking expired or soon-to-expire certificates
• SAN Extension Extraction: Extracts Subject Alternative Names, listing all protected domains and IPs
• File Drag & Drop: Supports dragging .pem/.crt/.cer files directly, or pasting PEM text

How to Use

1. Paste Certificate: Paste the PEM format certificate content into the input box, starting with -----BEGIN CERTIFICATE-----

2. Or Import File: Click the file selection area or drag a certificate file onto the page

3. Click Decode: Click the "Decode Certificate" button to parse the certificate content

4. View Results: After decoding, view subject, issuer, validity, public key, SAN extensions, and other details

5. Copy Results: Click the copy button to copy decoded results to clipboard for sharing or archiving

Use Cases

Case 1: Ops Troubleshooting SSL Issues

When a website shows SSL certificate errors, ops personnel can export the certificate and use this tool to quickly check details, determining if the issue is expiration, domain mismatch, or incomplete certificate chain.

Case 2: Developer Verifying Certificate Configuration

After configuring an HTTPS server, developers can check the SAN field to ensure all required domains are included, verifying multi-domain certificate configuration is correct.

Case 3: Security Auditor Analyzing Certificates

Security auditors can parse certificate signature algorithms, key lengths, and other security parameters to evaluate whether certificate strength meets requirements.

Case 4: Students Understanding PKI

Students learning cybersecurity can decode real certificates to intuitively understand X.509 structure, certificate chain trust relationships, and PKI principles.

Extended Knowledge

SSL/TLS certificates are based on the X.509 standard and are core components of HTTPS encrypted communication. Certificates are issued by Certificate Authorities (CAs) and contain public keys and identity information. Browsers verify website identity by checking the certificate chain (server cert → intermediate cert → root cert). Modern certificates widely use SAN extensions instead of the traditional Common Name for specifying protected domains, as Chrome and other browsers no longer check the CN field. The popularity of free CAs like Let's Encrypt has made SSL deployment easier, but correctly understanding and verifying certificate content remains essential for developers and ops personnel.