OpenDoor is a production-grade, open-source CLI web reconnaissance and directory enumeration scanner. It performs dictionary-based path discovery, subdomain enumeration, WAF detection, technology fingerprinting, and passive vulnerability detection (secrets, stacktraces, malware, open redirects). The architecture is a monolithic CLI application with a plugin-based design for response analysis and reporting, featuring a concurrent scanning engine, transport abstraction (direct, proxy, VPN), auto-calibration for false positive reduction, and session persistence. The codebase demonstrates high engineering standards with 99% test coverage, multi-OS CI, and comprehensive documentation. Several components, such as the redirect classifier, calibration engine, and thread pool, are well-isolated and exhibit high craftsmanship, making them potentially reusable in other projects.