The effect of germanium doping on the structural, magnetic, elastic and optical properties of the LiMgPdSn-type CoFeZrSi[Formula: see text]Ge[Formula: see text] alloys is predicted by utilizing ab initio density functional theory (DFT) with the generalized gradient approximation (GGA) and the electronic properties of the materials are investigated by using the generalized gradient approximation plus Hubbard coefficient (GGA + U). The estimated elevated lattice constant of CoFeZrGe compound agrees with existing theoretical data. The optimized lattice constants of CoFeZrSi[Formula: see text]Ge[Formula: see text](x = 0, 0.25, 0.50, 0.75) are 5.9022, 5.9631, 5.9752 and 5.9973 Å, respectively. These have been investigated for the very first time. The elastic symmetry (C[Formula: see text], C[Formula: see text], C[Formula: see text], C[Formula: see text], C[Formula: see text] and C[Formula: see text]), bulk modulus, shear modulus, Poisson’s ratio, anisotropy and Pugh ratio (B/G) are predicted and discussed. The calculation of band structure and density of states reveal that the materials considered have half-metallic behavior with 100% spin-polarization. The calculated magnetic moments of CoFeZrSi[Formula: see text]Ge[Formula: see text] are 0.99, 1.06, 1.02, 1.00 and 1.01 [Formula: see text], respectively, and agree with the SP rule, M[Formula: see text] = N[Formula: see text] − 24. The analysis of the elastic moduli indicates that the compounds are mechanically stable with a ductile nature. The CoFeZrSi[Formula: see text]Ge[Formula: see text] alloy is stiffer than the other compounds considered. Moreover, the dielectric functions, optical conductivity, reflectivity and absorption coefficient of CoFeZrSi[Formula: see text]Ge[Formula: see text] compounds are predicted by using complex dielectric functions.