testssl.sh is a mature, command-line Bash tool for comprehensive TLS/SSL security auditing of network services. It tests cipher support, protocol versions (SSLv2 through TLS 1.3), cryptographic vulnerabilities (Heartbleed, CCS, ROBOT, BEAST, POODLE, LOGJAM, FREAK, and many others), certificate validation, HTTP security headers, and STARTTLS on a wide range of protocols. The tool works by performing socket-level TLS handshakes and comparing results against embedded data files. It also includes a client simulation feature that replays ClientHellos from over 100 real-world browsers and libraries to detect server behavior differences. The architecture is a single large Bash script (testssl.sh) with supporting data files under etc/ and utility scripts in utils/. It is driven by command-line options and environment variables, producing output in terminal color, JSON, CSV, HTML, and log formats. The project has active maintenance with a thorough test suite and CI pipelines, though some data sources (e.g., SSL Labs API) are deprecated, and the client simulation data requires manual updates.