What problem does it solve? Machine-learning code often fails silently through preprocessing leakage, wrong cross-validation splitters, or drifted inference schemas. This Skill enforces explicit contracts for scikit-learn estimators, pipelines, splitters, and scorers so models are trained, evaluated, and deployed without hidden data leakage or contract violations. ## Core Features & Use Cases - Leakage-safe pipelines: Cross-validate preprocessing and classification as one cloneable unit so transformers never see validation data. - Group-aware splitting: Use GroupKFold with disjointness verification to prevent entity leakage across folds. - Inference schema guards: Reject drifted feature columns, duplicate names, and unexpected class mappings at prediction time. - Use Case: You are reviewing a teammate's training script and suspect the scaler was fit before the train/test split. Use this Skill to restructure the code into a Pipeline, pick the correct splitter, and add deterministic tests proving no leakage. ## Quick Start Ask the AI to review your scikit-learn training script for preprocessing leakage and rewrite it as a cross-validated Pipeline with the correct splitter and verification tests.