MicroWELT is implemented in Modgen, a freely available generic microsimulation programming language developed and maintained by Statistics Canada. This report documents the implementation of microWELT step by step and allows to reproduce the model from scratch. Most of the steps correspond to a new module that was added in this step. The documentation includes a description of each module as well as the modelling code. The steps are organized in such a way that basic concepts of modgen programming are introduced first. This allows the use of this documentation as a textbook for the implementation of microsimulation models.