Agricultural mitigation measures should be correctly designed and sited to make effective barriers for diffuse pollution. Landscape contexts of soils, slope, erosion and surface runoff generation differ across scales, farm types and management. A diversity of mitigation measures are being developed to improve trapping of key pollutants. There is a need to integrate knowledge on the functioning of these measures according to site context. We provide the narrative of concepts, evidence, workflow and testing of a decision support tool for selection between 16 field edge, riparian mitigation measures for protection of water quality. The tool uses question groupings to implement concepts of severity of runoff and erosion, surface and subsurface flow paths, waterbody and riparian condition. Landscape characterization provides scoring to rank or reject between the measures. The tool is intended for use by famers, advisors and catchment officers and is coded into an openly available webpage user interface.