DECALmachine is an extension for non-destructive, UV-less surface detailing using mesh decals. It provides an alternative approach to hard surface texturing by allowing users to project, slice, and generate decals from grease pencil strokes or edge selections. The toolset includes deep support for trim sheets, enabling placement, cutting, and manipulation directly within the 3D viewport. For game development workflows, DECALmachine supports creating decal atlases and baking decals directly to their parent object's UV space for export to engines like Unity and Unreal Engine. It features raycast-based insertion, automatic material matching, parallax effects in EEVEE, and tools for organizing and batch-creating custom decal libraries. The package includes a starter library of 109 decals, 64 trim decals, a trim sheet, and two atlases.