Free Tool

Free SSL Certificate Decoder & Analyzer

SSL/TLS certificates are the backbone of secure internet communication, but their encoded format makes it difficult to inspect what they actually contain. Our free SSL certificate decoder connects to any domain, retrieves its certificate, and displays every detail in a human-readable format - subject, issuer, Subject Alternative Names (SANs), validity period, key size, signature algorithm, and full chain of trust. Identify misconfigurations, weak algorithms, and expiring certificates before they cause outages.

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What This Tool Checks

Comprehensive analysis powered by Vysiro's scanning engines

Subject and issuer field extraction (CN, O, OU, C)

Subject Alternative Names (SAN) listing

Validity period and expiration date display

Key size and type analysis (RSA, ECDSA, Ed25519)

Signature algorithm identification

Certificate chain validation and display

Certificate Transparency (CT) log verification

Wildcard and multi-domain certificate detection

How It Works

Get results in seconds with our automated scanning process

Enter your domain name in the scanner above

We establish a TLS connection and retrieve the certificate

The certificate is decoded from its DER/PEM encoded format

We parse every field including subject, issuer, SANs, and extensions

Chain validation verifies the path from leaf to root CA

You receive a complete decoded certificate report

Frequently Asked Questions

Everything you need to know about ssl certificate decoder

What is an SSL certificate?

An SSL/TLS certificate is a digital document that authenticates a website's identity and enables encrypted communication between browsers and servers. It contains the domain name, the certificate authority that issued it, the public key, validity dates, and other metadata. Modern certificates use TLS (Transport Layer Security), though they are still commonly called SSL certificates.

What are Subject Alternative Names (SANs)?

Subject Alternative Names are a certificate extension that lists all the domains and subdomains a single certificate is valid for. For example, a certificate for example.com might also include www.example.com, api.example.com, and mail.example.com as SANs. This replaced the older practice of using separate certificates for each subdomain.

What key size should my certificate use?

For RSA certificates, 2048-bit is the current minimum recommended key size, with 4096-bit preferred for high-security applications. For ECDSA certificates, 256-bit (P-256) provides equivalent security to RSA-3072 with much better performance. Ed25519 keys offer the best performance-to-security ratio but have limited support.

What signature algorithms are considered secure?

SHA-256 with RSA (sha256WithRSAEncryption) or ECDSA (ecdsa-with-SHA256) are the current standard. SHA-384 and SHA-512 variants offer additional security margin. SHA-1 signatures are deprecated and rejected by all modern browsers. Vysiro flags any certificate still using SHA-1 or weaker algorithms.

How do I check if my certificate chain is complete?

A complete chain includes the leaf (server) certificate, any intermediate certificates, and traces back to a trusted root CA. Missing intermediate certificates cause validation failures in some clients. Our decoder shows the complete chain and flags any missing intermediates that could cause browser warnings.

What is Certificate Transparency?

Certificate Transparency (CT) is a framework that requires CAs to log all issued certificates in public, auditable logs. This helps detect misissued certificates and rogue CAs. Modern browsers require CT compliance (SCTs) for certificates to be trusted. Our decoder checks whether your certificate appears in CT logs.