LEFT is a free to use, web-based decision support tool originally developed to aid industry in evaluating the pattern of relative ecological value across a landscape to inform their planning of land use in order to minimize the environmental impact of their operations. A user defines an area of interest anywhere globally using a web-based map and the tool then automatically processes a series of high-quality datasets using standard published algorithms to produce maps at 300m resolution of landcover class, numbers of globally threatened terrestrial vertebrate and plant species, beta-diversity of terrestrial vertebrates and plants, habitat fragmentation, wetland habitat connectivity, numbers of migratory species and vegetation resilience. These results are aggregated to produce a single map of relative ecological value. The tool then generates a customised pdf report and a zip file of GIS data for the area requested. Results are delivered to users by email within a few minutes of job submission. This tool has been designed to be highly intuitive to use, and requires no specialized software or user expertise: novice users can submit an analysis within a few minutes and get results which can inform business decisions. www.biodiversity.ox.ac.uk/left