Aleatoric Engine is deterministic market simulation infrastructure for generating reproducible, schema-stable synthetic market data used in financial research, validation, and systems testing. It prioritizes explicit configuration, reproducibility, and operational clarity over statistical novelty or predictive modeling. Given the same SimulationManifest and seed, the engine produces identical outputs, enforces strict versioned schemas at boundaries, and emits provenance metadata with every run. Outputs include L2 order books, trade events, and funding events in Parquet, JSONL, or streaming form. Aleatoric Engine is infrastructure—not a predictive system—and it does not generate trading signals, optimize strategies, or forecast prices.