Any input file format supported by pymatgen. This includes CIF, POSCAR, CSSR and pymatgen JSON. See here for more information. Additional file formats might be supported on request.
{% hint style="danger" %} This is a known issue in some instances, where transformations may time out for certain larger crystal structures or combinations of inputs. Any transformation taking longer than 30 seconds will time out. {% endhint %}
Please ask on the Materials Project forum if this is a problem for you. We are improving this functionality over time. For advanced users, all transformations are also available for use via pymatgen.