SHAP (SHapley Additive exPlanations) is a mature Python library for interpreting machine learning model predictions using Shapley values from cooperative game theory. It provides a unified API across model types: tree ensembles (XGBoost, LightGBM, CatBoost, sklearn, PySpark), deep neural networks (TensorFlow, PyTorch), linear models, and arbitrary callables. The architecture is modular: explainers (Tree, Deep, Kernel, Partition, Gradient, Linear, etc.) consume models and maskers (tabular, image, text) to produce Explanation objects, which are visualized via matplotlib or interactive JavaScript force plots. The library includes benchmarks for evaluating explanation quality, extensive test suites with serialization baselines, and C++/CUDA extensions for performance. Although primarily a library (application), it has a strong research character: it originated from academic papers, includes notebooks reproducing experiments, and contains a user study on human interpretability. The codebase is well-engineered with reusable patterns (serialization, OpChain for lazy operations, MaskedModel abstraction), but carries some technical drift from legacy API aliases, dependency version sprawl, and a large minified JavaScript bundle in the repository.