HYTEC is a general purpose numerical simulation software designed for reactive transport (fluid flows of multiphase, multicomponent fluid mixtures in porous and fractured media), developed at the Centre for geosciences and geoengineering, Mines Paris, PSL University. **hytecio** is an open-source python library that provides tools to create, run, post-process and optimize HYTEC-based models using the latest Python standards. It aims to make setting up of a HYTEC simulation user-friendly by relying on existing well-established Python packages: - numpy: vectorized calculation of N-dimensional arrays, - meshio: input/output for many mesh formats, - pyvista: 3D plotting and mesh analysis through a streamlined interface for the Visualization Toolkit (VTK).