This tool facilitates the use of complex datasets in LPJ-GUESS by converting diverse land-use and vegetation data into model-ready input formats, enabling ecosystem simulations across both space and time. It manages heterogeneous data sources—spanning different time periods, spatial scales, and classification systems—by applying a consistent set of rules to harmonize landcover and stand-type information. In doing so, it produces the essential transition matrix and fraction files required by LPJ-GUESS, ensuring compatibility with both historical and future land-use scenarios in accordance with the model’s strict input specifications. The tool is built with flexibility and reproducibility in mind, allowing researchers to customize geographic domains, simulation periods, and land-use mapping rules to suit a wide range of scientific questions. Developed with open-source technologies such as Python, the codebase is clean, well-documented, and designed to support ongoing collaboration and further development within the LPJ-GUESS community.