The day-ahead market is the largest electricity market in Europe by traded volume, yet up-to-date simulation methodologies for reproducible research remain limited. iberian-day-ahead-market-simulator is a Python package to reproduce and analyze day-ahead market clearing in the MIBEL (which includes Spain and Portugal), with out-of-the-box compatibility with MIBEL public data. It enables reproducible experimentation with real day-ahead market data and provides a foundation for research on price formation, counterfactual scenarios, and policy analysis. We validated the package with more than 190 day-ahead market simulations, showing close agreement with observed outcomes in terms of prices, volumes, and cross-border exchanges.