📖 What is SSL Certificate Decoder?
SSL Certificate Decoder parses PEM-encoded SSL/TLS certificates and displays their details in a readable format — subject, issuer, validity dates, serial number, Subject Alternative Names (SANs), public key algorithm and fingerprint. Use it to inspect certificates before installation, verify cert chains, or debug TLS issues. Everything runs in your browser — your certificate data is never uploaded.
💡 Example
Input
-----BEGIN CERTIFICATE-----
MIIDxTCCAq2gAwIBAgIQ...
-----END CERTIFICATE-----
Output
Subject: CN=example.com
Issuer: CN=Let's Encrypt Authority X3
Valid: 2026-01-01 to 2026-03-31
SANs: example.com, www.example.com
🛠️ Common Use Cases
- Inspecting SSL certificate details before installation
- Verifying certificate chain and issuer
- Checking certificate expiration dates
- Viewing Subject Alternative Names (SANs) for multi-domain certs
- Debugging TLS handshake failures
📝 Certificate Fields Explained
- Subject — the domain or entity the certificate is issued to
- Issuer — the Certificate Authority (CA) that signed it
- Validity — start and end dates (Not Before / Not After)
- SANs — Subject Alternative Names, additional domains covered
- Public Key — algorithm (RSA, ECDSA) and key size
- Fingerprint — SHA-256 hash for identification
⚠️ Common Mistakes
- Missing intermediate certificates — your server must send the full chain, not just the leaf cert
- Expired certificates — check the Not After date and set up renewal alerts
- Wrong SAN entries — if the certificate does not include the exact domain (including www vs non-www), browsers will reject it
❓ Frequently Asked Questions
What format does this tool accept? ▾
PEM format — the text block starting with -----BEGIN CERTIFICATE----- and ending with -----END CERTIFICATE-----.
Can I check if my certificate chain is complete? ▾
Paste the full chain (leaf + intermediates) and verify the issuer of each certificate matches the subject of the next.
How do I find my SSL certificate? ▾
In most web servers, the certificate file is configured in the SSL/TLS settings (ssl_certificate in Nginx, SSLCertificateFile in Apache).
Is my data private? ▾
Yes — all processing runs entirely in your browser. Your data is never sent to any server.
Is this tool free? ▾
Completely free — no login, no usage limits, works offline once loaded.
Yes — completely free, no login required, no usage limits.
Is my data private? ▾
Yes — all processing runs in your browser. Your data is never sent to any server.
Does it work offline? ▾
Yes — once the page is loaded, the tool works without an internet connection.