This Python (v.2.7.10) code provides an estimate of the 3D structure of the chromatin fibre in cell nuclei from the contact frequency data produced by a ’Chromosome conformation capture’ experiment. The only input required is a text file containing a general real matrix of contact frequencies. The code features a GUI where all the tuneable parameters are made available to the user. The fibre is divided in independent segments whose structures are first estimated separately and then modelled as single elements of a lower-resolution fibre, which is treated iteratively in the same way until it cannot be divided anymore into independent segments. The full-resolution chain is then reconstructed by another iterative procedure. See the Readme file and the cited references for more detail.