SSL Certificate Decoder & Inspector
Parse PEM-encoded X.509 SSL/TLS certificates to inspect Common Names, SANs, validity, and expiration dates.
Subject (Issued To)
- Common Name (CN):
- -
- Organization (O):
- -
- Country / State / City:
- -
Issuer (Certificate Authority)
- Common Name (CN):
- -
- Organization (O):
- -
- Country:
- -
Validity Dates
- Valid From (Not Before):
- -
- Valid Until (Not After):
- -
Subject Alternative Names (SAN)
Cryptographic Properties
What is the Online SSL Certificate Decoder & Inspector?
The NexTools SSL Certificate Decoder is an online security utility designed to inspect, parse, and validate X.509 PEM certificates. Whenever web browsers establish secure HTTPS sessions, web servers present digital certificates to guarantee server identity and enable TLS encryption.
Engineered with a client-side ASN.1 DER parser, this tool decodes the certificate's metadata without transmitting your private keys or cryptographic certificates over the public internet. Instantly audit Common Names, all bound Subject Alternative Names (SANs), root Certificate Authorities (CAs), signature algorithms, and expiration countdowns.
Key Capabilities of SSL Certificate Decoder
Subject Alternative Names (SAN) Inspection
View every single domain name, wildcard pattern (*.domain.com), and subzone covered under multi-domain certificates.
Real-Time Expiration Warnings
Computes exact remaining days until expiration, highlighting upcoming certificate renewals before website outages occur.
Cryptographic Fingerprint Auditing
Inspects serial numbers, public key algorithms (RSA 2048/4096 or ECDSA P-256/P-384), and hashing algorithms (SHA-256).
100% Client-Side Privacy
All decoding logic runs locally in your browser. Zero certificate data or server tokens are ever transmitted to any third-party server.
Step-by-Step: How to Decode an SSL Certificate
- Obtain your PEM certificate: Open your
.crtor.pemfile in a text editor and copy the text including the-----BEGIN CERTIFICATE-----and-----END CERTIFICATE-----headers. - Paste into the Decoder: Paste the PEM text into the input field above, or click "Load Sample PEM" to test.
- Click "Decode Certificate": The tool parses the binary ASN.1 structures and displays the certificate details immediately.
- Audit Expiration and Domains: Check the expiration status badge and review all listed SAN hostnames.
Frequently Asked Questions (FAQ)
What is the difference between Common Name (CN) and SAN?
Historically, the Common Name (CN) represented the primary domain of an SSL certificate. Modern browsers (Chrome, Firefox, Safari) have deprecated CN verification and strictly enforce the Subject Alternative Name (SAN) extension, which lists all valid domains and subdomains covered by the certificate.
Can I paste my private key into this tool?
Never paste your private key anywhere. An SSL Certificate (starting with BEGIN CERTIFICATE) is a public document designed to be shared openly with clients. Private keys (starting with BEGIN PRIVATE KEY or BEGIN RSA PRIVATE KEY) must always be kept secure on your origin server.
What is PEM format?
PEM (Privacy-Enhanced Mail) is a base64-encoded ASCII container format for cryptographic keys and certificates, delimited by header and footer lines like -----BEGIN CERTIFICATE-----.
How long are SSL certificates typically valid?
Industry standards governed by the CA/Browser Forum cap public TLS certificate lifespans at 398 days (~13 months). Automated authorities like Let's Encrypt issue 90-day certificates to promote automated renewal cycles.