We present FoolProofJoint, a software tool that simplifies the assembly of laser-cut 3D models and reduces the risk of erroneous assembly. FoolProofJoint achieves this by modifying finger joint patterns. Wherever possible, FoolProofJoint makes similar looking pieces fully interchangeable, thereby speeding up the user’s visual search for a matching piece. When that is not possible, FoolProofJoint gives finger joints a unique pattern of individual fingers widths so as to fit only with the correct joint on the correct piece, thereby preventing erroneous assembly. In our benchmark set of 217 laser-cut 3D models downloaded from kyub.com, FoolProofJoint made groups of similar looking pieces fully interchangeable for 65% of all groups of similar pieces; FoolProofJoint fully prevented assembly mistakes for 97% of all models.