Summary: We explicitly evaluate the three-dimensional weight functions for a planar crack in an isotropic homogeneous material; these functions allow to obtain full stress intensity factors induced by a static point force applied at an arbitrary position. If we Fourier decompose the three-dimensional weight functions with respect to the \(z\) variable, then each Fourier mode satisfies the homogeneous equations of elasticity (except at the crack tip) and the boundary conditions on the crack face. Each Fourier mode diverges like \(r^{-1/2}\) near the crak tip, and decays exponentially for non-zero \(k_z\). We prove that these necessary conditions, which hold everywhere in the elastic material excluding the crack tip, are also sufficient to determine the three-dimensional weight functions. In particular, the three-dimensional weight functions can be calculated without considering an explicit loading problem.