We build a library to help inter-operability between codes in the field of quantum chemistry, primarily focused on enabling the communication of data between the flagship codes of the Targeting REal chemical accuracy at the eXascale (TREX) Center of Excellence (CoE) (NECI, GammCor, Quantum Package, QMC=Chem, CHAMP, TurboRVB, QML). We expect this library to be also adopted by the community beyond the TREX CoE. The data that needs to be stored in the electronic wave function, which is obtained from a post-Hartree-Fock calculation, or the one- and two-body density matrices, together with the one- and two-electron integrals that are necessary to compute the energy or other properties. As a wave function can be obtained by executing multiple codes in a complex workflow, the library should give the possibility to build the files incrementally using multiple codes.