LDR file is used by LDraw CAD program suite, a set of tools for creating 3D Lego models. LDR file contains all the information needed for 3D models, such as dimensions, coordinates, colors etc.

LDraw format is actively developed since its creation in 2003 and gathered a large following among Lego fans around the world. Projects in LDR files are commonly shared and discussed on dedicated internet forums.