TendonMech is an open-source finite element software for the computation of the mechanical response of tendon fascicles. The software simulates the fascicle structure, accounting for both its inner composite fiber–matrix nature and for its helical structural arrangement. It allows for the simulation of a wide range (35%–65%) of fibrillar contents. The model exploits the periodicity of the helical domain, simulating the fascicle's mechanical response through the discretization of a fascicle cross section. Thereupon, it computes the effective fascicle elastic modulus, Poisson's ratio value and coupling torsional stiffness.