🔒 SSL Checker

When you enter a hostname, the checker uses Python's ssl module to establish a TLS connection to the target server on port 443. During the TLS handshake, the server presents its SSL/TLS certificate, which contains the server's public key, identity information, validity period, and cryptographic signatures. The tool extracts this certificate and analyzes its contents without trusting the server's certificate chain — it reads the raw certificate data directly. It then verifies the certificate chain by traversing from the leaf certificate (the one presented by the server) up through any intermediate certificates to a root Certificate Authority (CA) that is trusted by the system's certificate store. The tool reports the certificate's Subject Alternative Names (SANs) to verify which domains and subdomains it covers, checks the not-before and not-after dates to confirm validity, identifies the issuing CA and key algorithm (RSA or ECDSA with key size), and reports the signature algorithm used. It also checks whether the certificate supports modern TLS versions (1.2 and 1.3) and whether the chain is complete without missing intermediates.

The certificate chain verification is critical for browser trust. When a browser encounters an incomplete chain — where the server presents its leaf certificate but not the intermediate certificates — it must download the missing intermediates itself, which can fail and produce security warnings. The tool explicitly checks whether the server provides the full chain during the handshake. It also validates that each certificate in the chain is properly signed by the next one up, and that the root certificate exists in a recognized trust store. The key algorithm and size assessment checks whether the certificate uses a modern, secure configuration — RSA keys should be at least 2048 bits, and ECDSA keys should be at least 256 bits. The tool also reports the certificate's fingerprint, which can be used to verify that the same certificate is presented consistently across multiple server instances behind a load balancer.

Common Use Cases

DevOps engineers verify SSL certificates are valid and properly configured before deploying to production, catching issues like missing intermediate certificates or incorrect domain coverage that would cause browser warnings. Site reliability engineers monitor certificate expiration dates to plan renewals well in advance, preventing unexpected outages when certificates expire. Security auditors check certificate key strength and algorithm choices to ensure they meet current security standards, flagging weak configurations like RSA-1024 or SHA-1 signatures. Web developers debugging mixed content warnings and certificate errors use the tool to understand exactly what the server is presenting to browsers. Hosting administrators troubleshoot Let's Encrypt certificate installations to verify the ACME challenge process completed correctly and the certificate chain is properly deployed.

Security & Privacy Considerations

The tool initiates a standard TLS handshake, which is the same process any web browser performs when connecting to an HTTPS site. The server's SSL certificate is public information by design — it is presented to every client that connects, which is fundamental to how PKI (Public Key Infrastructure) works. No data beyond the public certificate is accessed or transmitted. The tool does not attempt to downgrade connections, exploit known vulnerabilities like Heartbleed or POODLE, access private key material, or perform any active attack against the server. Results are not stored on our servers. For comprehensive SSL testing including cipher suite enumeration, protocol version scanning, and known vulnerability checks, dedicated tools like Qualys SSL Labs provide more thorough analysis. The tool is designed for quick, non-invasive certificate inspection that is safe to use on any production server.

Frequently Asked Questions