Input and output rails as ordinary Ruby objects, returning passed, modified, or blocked, and reporting whether a rail actually reached the decision. Deterministic rails need no network at all; model-backed ones call any OpenAI-compatible endpoint through a provider abstraction that prefers a local proxy. Reads and writes NeMo Guardrails configuration folders and executes their Colang flows in process, with an optional client for teams who already run the Python server. Standard library only.