We present a novel, open source 3-D MT forward solver based on a method of integral equations (IE) with contracting kernel. Special attention in the solver is paid to accurate calculations of Green's functions and their integrals which are cornerstones of any IE solution. The solver supports massive parallelization and is able to deal with highly detailed and contrasting models. We report results of a 3-D numerical experiment aimed at analyzing the accuracy and scalability of the code. •New 3-D magnetotelluric forward open source code is presented.•The code shows very good performance in terms of accuracy and run time.•Code accuracy is attained by a new scheme for estimating Green's function integrals.•The implemented scheme of parallelization provides strong scalability of the code.