SSL/TLS Certificate Checker

This tool queries Certificate Transparency (CT) logs to retrieve SSL/TLS certificate information for any domain. CT logs are public, append-only records of certificates issued by Certificate Authorities (CAs), providing transparency and accountability in the certificate ecosystem.

What is an SSL/TLS Certificate?

An SSL/TLS certificate is a digital document that authenticates a website's identity and enables encrypted connections. When you visit a site over HTTPS, the server presents its certificate to prove it is who it claims to be.

Certificate Details Explained

• Common Name (CN): The primary domain the certificate was issued for
• Issuer: The Certificate Authority (CA) that issued the certificate
• Valid From / To: The time window during which the certificate is valid
• Serial Number: A unique identifier assigned by the CA
• Subject Alternative Names (SANs): Additional domains covered by the certificate

Why Check Certificates?

• Expiration Monitoring: Expired certificates cause browser warnings and downtime
• Security Auditing: Detect unauthorized or misissued certificates for your domain
• Compliance: Verify certificates meet organizational security policies
• Transparency: Monitor CT logs for unexpected certificate issuance

Certificate Transparency

Certificate Transparency (CT) is an open framework (RFC 6962) designed to detect misissued certificates. CAs are required to log all issued certificates to public CT logs. This tool queries these logs via crt.sh, a widely used CT log search engine maintained by Sectigo.

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