Free SSL Certificate Checker: Real-Time TLS Validation and SAN Analysis

SSL Certificate Checker — enter any domain, get full SSL certificate details.

Developer Manja has launched an SSL Certificate Checker that provides deep-level visibility into domain security. The system utilizes raw TLS connections to extract peer certificates, bypassing standard HTTP requests.

Why This Matters

Manual certificate auditing often relies on browser UIs which can obscure technical details like Subject Alternative Names (SANs) or specific protocol versions like TLS 1.3. This tool addresses the gap between ideal automated renewal monitoring and the technical reality of complex multi-domain deployments that require granular verification of key sizes and fingerprints to prevent unexpected service outages.

Key Insights

• Direct TLS handshake extraction (2026) provides certificate data without the need for HTTP overhead.
• Protocol identification for TLS 1.2 and 1.3 ensures compliance with modern encryption standards.
• SAN analysis allows verification of all subdomains and aliases covered by a single certificate for configuration accuracy.
• Key size reporting identifies 256-bit and 2048-bit encryption strengths to audit against security requirements.
• Serial number and fingerprint extraction enables precise certificate tracking and authenticity verification.

Practical Applications

• Use case: Verifying certificate issuer and SANs immediately after a server migration to ensure correct deployment.
• Pitfall: Relying on manual browser UI checks which may not reveal hidden certificate chain issues or protocol version mismatches.
• Use case: Auditing third-party domains to verify that external dependencies meet internal security protocol standards.

References:

• https://dev.to/manja316/free-ssl-certificate-checker-see-expiry-issuer-sans-for-any-domain-1jn
• https://sslcheck-zeta.vercel.app