Fitter is used as a part of a program complex on spectrometer YuMO. It is designed to be easily is understood by the experimenters. Both command line interface and GUI are provided. Despite of simplicity of offered models wide usage of fitter for many major appendices is supposed. The further development of the program is connected to expansion of offered models and introduction in the program of processing of the account of the structural factor. Fitter's design allows the simple adding of new models.