Start a fresh build on an empty baseplate of width x depth studs. Replaces the current build (previous one stays saved on disk).

List every part in the catalog (the ONLY placeable pieces) and all colors. Sizes are studs; height is in plates (brick=3, plate/tile=1). Tiles have smooth tops. Slopes have studs only on their non-sloped rows (at rotation 0 the slope descends toward +y; rotate 90/180/270 to face it). Baseplates have studs on top, nothing underneath, and only go at z=0.

Place a part with its minimum-x,y corner at stud (x,y), bottom at plate height z (z=0 on the ground; on top of a brick placed at z=0 means z=3). rotation is 0, 90, 180 or 270 (90/270 swap the footprint; slopes descend toward +y at 0 and rotate with the piece). Fails with an explanation if the placement collides, floats, or leaves the build area.

Remove a piece by id. Refused if other pieces would be left floating.

Current build state: piece list with positions, inventory, dimensions.

Top-down ASCII map of each plate layer (pieces shown by id, '.' empty). Optionally limit to plate range [z_from, z_to).

Load a previously saved build by name (see saved .json files in builds/). The save is re-validated piece by piece on load.

Export the build. fmt='ldraw' writes builds/.ldr (openable in BrickLink Studio / LeoCAD); fmt='blender' writes builds/_blender.py, a bpy script that constructs the model in Blender.