Because the server lives inside the application, every command lands in the live document: an agent can raise walls, drop catalog furniture into them, set a camera and ask for a Sunflow render or an OBJ export without a file changing hands. Object IDs are stable UUIDs across calls, coordinates are in centimetres, and checkpoints let you snapshot the scene before letting it attempt something larger.
A Sweet Home 3D plugin that runs the MCP server inside the application itself, over HTTP on port 9877 at http://127.0.0.1:9877/mcp. There is no proxy and no second process: the assistant edits the document you are looking at, across 42 commands in 12 categories.
- Walls and rooms: create_wall between two points, create_walls for a rectangular room, modify_wall for height, thickness, colour, arc and coordinates, connect_walls so corners render correctly, create_room_polygon from a list of points
- Furniture from the built-in catalog — list_categories and list_furniture_catalog to browse, place_furniture to place, modify_furniture to move, rotate, resize or recolour, plus group_furniture, ungroup_furniture and duplicate_objects
- place_door_or_window works out the position and angle inside the wall for you
- Textures and appearance: list_textures_catalog, apply_texture onto a wall side or a room surface, set_environment for ground and sky colour, lighting, wall transparency and drawing mode
- generate_shape builds custom geometry — box, sphere, cylinder, cone, wedge, arch, stairs, torus, hemisphere and pipe, plus extrude, mesh and boolean union, subtract and intersect
- Output in four forms: render_photo for a ray-traced Sunflow image, export_plan_image for a PNG plan, export_svg, and export_to_obj for the 3D scene with materials and textures
- Multi-storey plans through add_level, list_levels, set_selected_level and delete_level, and add_label and add_dimension_line for annotation
- checkpoint, restore_checkpoint and list_checkpoints give an in-memory undo timeline, and batch_commands sends several commands in one request
Sweet Home 3D 6.0 or newer on Java 11 or newer. Download the .sh3p plugin from the repository's releases, drop it into the Sweet Home 3D plugins folder and restart — the server then starts on port 9877 by itself, and Tools → MCP Server… shows its status and can write the Claude Desktop config for you. Point the client at http://localhost:9877/mcp as an HTTP server. The Mac App Store build is sandboxed and cannot open a listening socket, so use the standalone build from sweethome3d.com instead.