Kingfisher is an open-source secret scanning tool developed by MongoDB's Staff Security Engineer to detect and validate exposed secrets in code repositories, Git commit histories, and file systems. It is designed for high-performance, real-time validation, and goes beyond traditional secret scanners by actively validating detected secrets against external systems. Kingfisher supports a rich set of rules defined in YAML files, multi-threaded scanning, and cross-platform support. It helps security teams catch exposed secrets, identify active risks, and strengthen source code integrity, ultimately supporting Supply-chain Levels for Software Artifacts (SLSA) compliance. The tool has been built using Rust, Hyperscan, and Tree-sitter technologies, providing memory safety, high-speed regular expression matching, and accurate source code parsing. Kingfisher is now being released to the broader community to empower developers and security teams to protect their critical assets against evolving cyber threats.