Describe it. Point at it. Tweak it.
Three ways to shape a part, and they all end in the same place: one build123d script that the exact kernel executes. No feature tree, no hidden state, nothing you cannot read.
Describe
“60 × 40 × 8 plate, four Ø5 holes 8 mm from the corners, a Ø20 boss with a Ø8 bore.” Attach a photo or a napkin sketch if you have one. The agent writes the model with named dimensions.
Point
Click a face, an edge or a body and it becomes a chip on your message, with its exact type, centre, normal and size. The agent works on that face, not a guess.
Tweak
Press/pull, holes, fillets, chamfers, shells and sketches from a Fusion-style ribbon, or change a number in the Parameters card. Written into the same script, undoable, visible to the agent.
Point at a face. See what the agent sees.
This viewer runs the app's renderer on meshes baked from the real kernel. Hover and click faces: the chip and the [Selected geometry] block are exactly what a chat message carries.
Because the message carries the geometry, the agent can write faces().sort_by_distance((x, y, z))[0] and hit the face you meant, then confirm with inspect_model or a screenshot. Every rebuild renumbers faces, so the app matches chips again by type and centre.
“I just want to tweak it.”
Sometimes you know exactly what you want and do not want to say it. The ribbon works like a desktop CAD tool: pick, type a number, ↵. A command dialog walks you through each tool with a live prompt, chips for what you picked and unit fields. Under the hood the operation is appended to the body's expression in the script, so it is undoable, reproducible and visible to the agent.
_plate = plate.part
_plate2 = _plate + extrude(_plate.faces().sort_by_distance((7, 0, 19))[0], amount=5, dir=(0, 0, 1))
_plate3 = tap(_plate2, "M4", at=(18, 0, 4), depth=6, axis=(0, 0, -1))
result = {"Plate": _plate3.fillet(2, [*_plate3.faces().sort_by_distance((7, 0, 24))[0].edges()])}Hover a tool. Shortcuts match the app: B C O K create, Q H F X L V modify, I measure, D drawings, P slice.
Sketches on any face
Select a face, press K: rectangles, circles, polygons and slots with grid snap. Stored as an editable block that is also a real Sketch the agent can extrude, cut or revolve.
Metric and inch threads
ISO metric (M4) and Unified inch (1/4-20, #10-32): tap drill, clearance, hex and socket heads, nuts and washers from the tables. tap(part, "M4", …) cuts the hole and drawings call it out as M4×0.7.
Parameters and measure
Every top-level number is a field. Measure snaps to vertices, edges and faces: lengths, radii, angles, hole spacing, mass, clearance between bodies.
Exact B-rep, not triangles
Planes, cylinders, cones, spheres, tori and B-splines from OCCT. The display mesh has exact normals; the geometry underneath is analytic.
