Data handling for energy system optimisation models is a necessary but tedious task. Depending on the workflow, user skill level, and model implementation, the data interfacing requirements can be significantly different. OSeMOSYS Tools for Energy Work, or otoole, is a Python package providing OSeMOSYS energy modellers with options to use different input dataformats, visualize and validate input data, and process result data. otoole exposes three different input data formats to the user, can process result data from four popular solvers, and is designed to be modular and extensible to enable interoperability between OSeMOSYS models developed in different programming languages.