Understanding groundwater-surface water (GW/SW) interactions is fundamental to hydrologic system integrity, particularly in arid and semi-arid regions where unsaturated zone processes exert a dominant influence on recharge, discharge, and interaction dynamics. Despite its importance, existing assessment frameworks often lack spatial adaptability and fail to account for local hydrogeologic complexity, data limitations, and implementation constraints. This study introduces the Iranian Groundwater-Surface Water Interaction Method Selection Decision Tool (IR-GWSW-IA-MSDT), a modular, semi-quantitative framework designed to facilitate scientifically robust and context-sensitive selection of GW/SW assessment methods. The tool synthesizes hydrogeological and socioeconomic indicators, spatially calibrated across 609 officially delineated study areas in Iran, to quantify the relative importance of GW/SW interactions. It employs a dual-pathway decision structure: the first ranks candidate methods based on their alignment with interaction importance scores and expert-assessed accuracy; the second filters methods according to user-defined objectives, data availability, technical feasibility, and site constraints. Evaluations incorporate both compatibility and functional adequacy across interaction types, including river-aquifer interaction, return flow, and precipitation-driven recharge. Application to three representative basins-Dezful-Andimeshk, Tehran-Karaj, and Urmia-demonstrates the tool's capacity to recommend hydrologically appropriate and operationally feasible methods across diverse GW/SW regimes. Unlike conventional frameworks, IR-GWSW-IA-MSDT explicitly integrates unsaturated zone dynamics and enables flexible reconfiguration for regional or international contexts. By aligning method selection with both environmental relevance and institutional capacity, the tool supports improved groundwater-surface water governance and contributes to sustainable development goals (SDGs), particularly SDG 6 (Clean Water and Sanitation) and SDG 13 (Climate Action).