Analyze SSL/TLS certificate configurations and security best practices. Check certificate fields, validity, chain of trust, and common misconfigurations — educational and informative.
Certificate Score
SSL Certificate Checker is a free tool that analyzes PEM-encoded SSL/TLS certificates. Paste a certificate and get detailed information about its signature algorithm, key size, format, and detected domains. The tool evaluates the certificate against security best practices and provides a score with actionable recommendations. All analysis happens in your browser — the certificate data is never sent to any server.
Use this tool when you need to inspect a certificate's properties, verify that it uses a strong signature algorithm (SHA-256 or better), check the key size meets minimum requirements, or learn about SSL/TLS certificate best practices. It is useful during certificate renewals, security audits, and when troubleshooting SSL/TLS configuration issues.
Security engineers use this tool to verify certificate properties during renewal processes, check that deprecated algorithms (SHA-1) are not in use, inspect certificates exported from web servers or key stores, evaluate certificate chain components, and document certificate details for compliance audits. Developers use it to understand certificate structure and learn about X.509 fields.
Essential terms and definitions related to SSL Certificate Checker.
A digital document that authenticates a website's identity and enables encrypted communication. It contains the domain name, organization info, public key, issuer (Certificate Authority), and validity period. Browsers display a padlock icon when a valid certificate is present, indicating the connection is encrypted.
A trusted organization that issues digital certificates after verifying the identity of the certificate requester. Major CAs include Let's Encrypt (free, automated), DigiCert, Comodo, and GlobalSign. Browsers and operating systems maintain a list of trusted root CAs to validate certificate chains.
The hierarchical chain from a server's certificate through one or more intermediate certificates to a trusted root certificate authority. Each certificate in the chain is signed by the next, forming a trust path. Browsers validate this entire chain to ensure the server certificate is authentic.
A certificate extension that allows a single certificate to secure multiple domain names (e.g., example.com and www.example.com). Modern browsers require the domain to be listed in the SAN field rather than just the Common Name (CN). Wildcard certificates (*.example.com) use SAN to cover all subdomains of a domain.
This tool operates in educational/analysis mode. It helps you understand SSL certificate fields, evaluate certificate configurations you paste in, and learn about best practices. Browser security restrictions prevent direct SSL certificate inspection from client-side JavaScript. For live certificate checking, tools like openssl s_client or server-side checkers are needed.
The tool accepts PEM-encoded certificates (the text format starting with -----BEGIN CERTIFICATE-----). This is the most common format used by web servers, Let's Encrypt, and certificate authorities. You can export certificates in PEM format from your browser or server configuration.
Key things to verify: the certificate is not expired (check notBefore and notAfter dates), the subject/SAN matches your domain, the issuer is a trusted Certificate Authority, the key size is at least 2048 bits for RSA or 256 bits for ECDSA, and the signature algorithm uses SHA-256 or better (not SHA-1).
SSL (Secure Sockets Layer) is the predecessor to TLS (Transport Layer Security). SSL versions (1.0, 2.0, 3.0) are all deprecated due to security vulnerabilities. Modern secure connections use TLS 1.2 or TLS 1.3. The term "SSL" is still commonly used colloquially to refer to TLS certificates and connections.
Common errors developers encounter and how to resolve them.
Certificate not recognized or parse error Ensure the certificate is in PEM format, starting with -----BEGIN CERTIFICATE----- and ending with -----END CERTIFICATE-----. The content between the markers should be Base64-encoded DER data. Remove any extra whitespace or blank lines within the Base64 block.
Certificate shows as expired Check the notAfter field — if the current date is past this date, the certificate has expired and must be renewed. For Let's Encrypt certificates, the validity period is 90 days. Set up automatic renewal with certbot or your hosting provider to prevent expiration.
Certificate chain incomplete warning Web servers must send the full certificate chain (server cert + intermediate certs) for browsers to validate trust. If intermediate certificates are missing, some clients will fail to establish a secure connection. Check your server configuration to ensure all intermediate certificates are included in the chain file.