Аннотация:SpectrRelax has a large number of built-in models and a way to express linear and not linear dependencies between model parameters. Unfortunately it becomes rather difficult to work with models as the number of subspectra and analytical expressions of model parameters increases. To overcome this difficulty we implemented a way to extend SpectrRelax with user-defined models. These models are written in Lua language and are transparently integrated into the application. Extension mechanism demonstrated on the example of the Laves model for processing and analysis of spectra of 57Fe nucleus in the rare earth laves phases with a C15 structure.