Characterization of high brightness electron beams has become crucial to ensure reliable operation of radiofrequency and plasma-based linear accelerators, for example aimed at extending free-electron lasers’ longitudinal coherence to the water window and beyond. To date, this goals are often prevented by the detrimental effect of spurious harmonic content in the longitudinal profile of electron bunches, known as microbunching instability. In a series of recent works, inclusion of intra-beam scattering in microbunching model has proved to be an essential step to more faithful predictions of the beam energy spread. Analytical expressions for intra-beam scattering in single pass linacs and multi-bend transfer lines are presented and included in two different semi-analytical description of microbunching. The overall modeling turns out to be a fast comprehensive tool for the optimization of linac-driven free-electron lasers.