TLS Version Checker

How the TLS Checker Works

What the Tool Does

The TLS Checker probes a hostname's TLS configuration by attempting connections at each protocol version (TLS 1.0, 1.1, 1.2, and 1.3) and reports which versions are supported. It also retrieves the server's X.509 certificate details including subject, issuer, validity dates, SANs, and key size. The check runs via a server-side API to avoid browser security restrictions on raw TLS socket access.

Common Developer Use Cases

DevOps engineers use TLS checkers to verify that deprecated protocols (TLS 1.0/1.1) are disabled after configuration changes, ensuring PCI-DSS compliance. Developers debug certificate chain issues, check expiration dates before renewals, and confirm that wildcard or SAN certificates cover all required subdomains. Security auditors scan endpoints to identify weak protocol support that could expose services to downgrade attacks like POODLE or BEAST.

Data Formats, Types, or Variants

TLS versions range from 1.0 (1999, deprecated) through 1.1 (2006, deprecated) to 1.2 (2008, widely supported) and 1.3 (2018, fastest and most secure). The certificate information includes the subject Common Name and Subject Alternative Names (SANs), issuer chain, RSA/ECDSA key type and size, signature algorithm, and not-before/not-after validity timestamps. Results indicate whether each protocol version handshake succeeded or was rejected by the server.

Common Pitfalls and Edge Cases

CDNs and load balancers may present different certificates or TLS configurations than the origin server, so always test the actual endpoint your users connect to. SNI (Server Name Indication) is required for hosts serving multiple certificates on one IP — testing by IP address alone may return the wrong certificate. Some servers use TLS termination proxies where the proxy supports TLS 1.3 but the backend only speaks 1.2, giving a misleading impression of the full chain's security posture.

When to Use This Tool vs Code

Use this browser tool for quick ad-hoc checks of individual endpoints during incident response, certificate renewal verification, or compliance spot-checks. For continuous monitoring of TLS configurations across many endpoints, use dedicated tools like testssl.sh, sslyze, or cloud-based certificate monitoring services that provide alerting, historical tracking, and automated scanning schedules.