Principles helps teams keep an agent's operating guidance consistent as their harness evolves. Name a principle and map the instruction passages, rules, skills, agents, hooks and checks that carry it. The principles CLI reports changed or broken members and guides the agent through assessing the whole set, fixing problems or recording open findings, and keeping the map and audit history in version control. The CLI tracks state and validates references deterministically; the consuming agent supplies the judgement. It calls no model and never edits the project's guidance. Structured results provide the next command, evidence requirements and repairs. Context-loading information helps the agent assess unnecessary guidance. The gem provides a host-independent command-line runtime for Ruby 3.4.x with no runtime gem dependencies.