Serpentine3D

An open-source NURBS surface modeller for Linux, Windows & macOS — a Rhino-style freeform workflow with native AI integration.

Download for Linux · Windows · macOS · Website

Serpentine3D (serp3d) is a freeform surface modeller in the spirit of Rhinoceros 3D — BREP/NURBS geometry on the OpenCASCADE kernel, not meshes. It is built for set designers, architects, and industrial designers who want a genuine Rhino-style workflow: a command line that prompts for input, layers, object snaps to a construction plane, STEP/OBJ/FBX interchange, and a dark, focused interface. The whole modelling engine also runs headless, so the same geometry you build by hand can be scripted, batch-processed, or driven by an AI.

Named after the serpentine stone of Zimbabwean Shona sculpture, and the S-curve at the heart of NURBS geometry.

Why

• No open-source freeform NURBS surface modeller exists. FreeCAD is parametric solid CAD; Blender is mesh-based. Serpentine3D fills the freeform surface-modelling gap — on Linux, Windows and macOS alike.

• First CAD tool with native AI integration. The bundled MCP server lets Claude (or any MCP client) see your viewport, create geometry, run any command, and manage the scene.

• Headless-first. The modelling core is fully decoupled from the GUI — script it (serp3d-batch), import it as a Python library, or drive it over MCP. Repeatable, configurable, light, CI-friendly.

Related MCP server: Maya MCP Server

Install

Download

Each download bundles the OpenCASCADE kernel and Python runtime — nothing else to install. The GUI needs a GPU with OpenGL 3.3 drivers, which any normal desktop has; GPU-less VMs and remote-desktop sessions that only expose OpenGL 1.1 get a clear message instead of a viewport. Headless use (serp3d-batch, the MCP server, file conversion) works anywhere.

From source

Requires Python 3.10+.

git clone https://github.com/chisomobanzi/Serpentine3D && cd Serpentine3D
python3 -m venv .venv
.venv/bin/pip install -e .
.venv/bin/serp3d        # launch

The OpenCASCADE kernel installs as pip wheels (cadquery-ocp) — no conda, no system packages. The same install works on Linux, Windows and macOS; the full test suite (360+ tests) passes on all three.

The command line

Everything works Rhino-style: type a command, answer its prompts. Prompts accept typed coordinates (10,5,0, relative @5,0,0) or viewport clicks on the construction plane. Tab completes command names, Up/Down recall history, Enter on an empty line repeats the last command, Escape cancels. As in Rhino, a right-click in the viewport acts as Enter — it runs whatever you've typed, commits a value mid-command, or repeats the last command.

Most commands have Rhino-compatible aliases (l, pl, c, m, co, mi, ...). Command options appear as clickable chips under the prompt (Cap=Yes, BothSides=No, Style=Normal) and can be typed Rhino-style (cap=n) at any moment without losing your place; numeric prompts show a live gold ghost preview of the result while you type. help (or F1) opens a searchable command reference. Arrow keys nudge the selection along the CPlane (Shift ×10, Ctrl ×0.1).

Navigation & shortcuts

• Middle mouse orbit in perspective, pan in Top/Front/Right · Shift+Middle pan · Ctrl+Middle orbit anywhere · Scroll zoom

• F1–F4 top/front/right/perspective · Ctrl+E zoom extents · F7 grid

• Ctrl+Z / Ctrl+Y undo/redo · Ctrl+A select all · Delete delete selection

• Ctrl+S / Ctrl+O / Ctrl+N save/open/new

• Click to select (Shift-click adds, Ctrl-click removes), click empty space to deselect

• Box selection: drag left-to-right for a window (fully enclosed, gold box), right-to-left for a crossing (anything touched, white box); Shift adds, Ctrl removes

• Control points: pointson (F10) shows CVs on curves — drag a CV to edit the curve live; pointsoff (F11) hides them

• Object snaps — end, mid, center, quadrant, intersection, perpendicular, and nearest-point, each with a distinct cursor marker. Toggle types on the osnap bar under the command line, or in Settings. gridsnap snaps picked points to the grid

• Launch with a file: serp3d model.serp (or any importable format)

Drafting & documentation

Serpentine3D has a full two-space drafting workflow — model in 3D, document in 2D, print to PDF — without leaving the app:

• Layouts (layout): paper-space sheets (A4–A0, Letter, Tabloid or custom) with tabs at the bottom of the viewport: [Model] [Sheet 1] …

• Detail views (detail): live windows into the model placed on the sheet — pick two corners, a view direction (top/front/right/…/perspective) and a scale (1:10, 1:50, …). Double-click a detail to enter it, then pan (nav-button drag) and zoom (wheel changes the scale); click outside to exit. detailscale, detailmode, detaillock, detailborder, detaildelete manage the active detail.

• Hidden-line rendering: each detail can be technical (hidden lines removed), hidden (dashed hidden lines), wireframe or shaded — powered by OCCT's HLR engine, isolated in a worker process so degenerate geometry can never crash the app. The same engine drives the model-space technical display mode.

• make2d: project the current view (or a selection) into real, editable 2D curves on Make2D visible / Make2D hidden layers.

• Annotations: multiline text, leader, dim / dimradius / dimdiameter / dimangle, hatch (pick corners or Mode=Region to click inside detail linework), scalebar, titleblock, sheetindex and per-sheet revision tables. Everything on a sheet is selectable — drag to move, grips resize detail frames, Delete removes, annotedit edits — and dimensions picked inside a detail are associative: they re-project when the detail pans or rescales. dimstyle manages named text/arrow styles.

• exportpdf (Ctrl+P): true vector PDF — linework stays crisp at any zoom; shaded details are embedded as rendered images. Layouts save/load with the .serp file.

The gumball

Select anything and a gumball appears: drag the arrows to move along an axis, the pads to move in a plane, the circles to rotate (Shift snaps to 15°), the square knobs to scale along an axis (Shift = uniform). Alt-drag moves a copy. Escape cancels a drag. gumball toggles it.

Ctrl+Shift-click a face of a solid and the gumball becomes a push/pull handle along the face normal — drag it, or type a distance, to extrude the face outward or carve it inward; the solid rebuilds live and the handle stays on the moved face for repeated pulls. A curved face (a cylinder or cone wall, a sphere) offsets instead — push it to grow or shrink the radius, adjacent faces extending to meet it. Select several faces and one handle offsets them all together, each along its own normal — inflate a shape, or grow a slab from both sides at once.

Each axis carries two boxes. The filled one on the shaft extrudes: a curve grows a surface along the axis and stays where it is, a closed curve gives you the solid it encloses, and a surface becomes the solid it sweeps out. A selected edge grows a surface of its own and leaves the object it came off alone. The filled box only appears on an axis where there is something to grow, so a solid does not offer one at all, and a flat surface offers one only on the axis it faces: swept the other two ways it would come back as the surface it already is. Ctrl and a translate arrow does the same thing if that is the habit you arrived with.

The hollow box on the far side of the pivot, at the end of the dashed leader that mirrors the arrow, is scale. Type a distance for either instead of dragging.

Ctrl+Shift-click one or more edges and the gumball becomes a fillet handle — drag it outward, or type a radius, to round the edges; every selected edge fillets together at that radius, previewing live. Hold Alt while dragging to chamfer instead of fillet.

Units

units sets the document units (mm/cm/m/in/feet-and-inches) with an optional model rescale. Every prompt then accepts unit input — 3'6", 2' 4 1/2", 30cm, 1.5in — and coordinates support polar entry (10<45) and Shift-ortho constraint while picking. Tab locks the direction you are pointing in for any direction, not just the four ortho ones, leaving the cursor to set only the distance along it.

Scripting & automation

The modelling engine runs with or without a GUI, so anything you can do by hand can be automated:

• Python console (Tools menu, Ctrl+`): the live scene, geometry builders and the full API in an interactive session.

• serpentine3d.scripting.Document: the same power headless — doc.add(geo.make_box(...)), doc.run("filletedge", [...]), doc.export("part.step"). The command layer is decoupled from Qt, so every interactive command runs offscreen.

• serp3d-batch script.py: run scripts from the command line / CI with doc, geo and args predefined. No display needed.

• MCP server (serp3d-mcp): the same modelling surface as tools an AI agent can call — full CRUD over the scene (see below).

• Autosave & crash recovery: every 5 minutes (configurable); on launch after a crash Serpentine3D offers to restore the autosave.

• Drop a ~/.config/serpentine3d/template.serp to start every new document from your own template (units, layers, title blocks).

Settings

Tools → Settings (Ctrl+,) — five flat pages, changes apply instantly:

• Mouse — orbit with the middle or right mouse button, scroll direction, orbit/zoom speed

• Keyboard — bind any key to any command; import from a text file (F5 zoomextents per line) or JSON

• Aliases — custom command aliases; imports Rhino alias exports (Options → Aliases → Export) and maps known commands automatically

• Object Snaps and Display (grid size)

Settings live in ~/.config/serpentine3d/settings.json.

File formats

The assistant (AI modelling)

Serpentine3D has a built-in AI assistant: open it from the View menu (or type ai, or Ctrl+Shift+A), describe what you want, and it builds real BREP geometry in your live scene —

a spiral staircase, 3 m tall, 14 steps, 900 mm radius fillet every edge of the box 2 mm what's the volume of the hull?

It works with the full command set (the same commands you type), can measure and inspect the scene, and can look at the viewport — it takes a screenshot, checks its own work, and fixes mistakes before answering. Everything it does streams into the panel as it happens, and everything is undoable.

Bring your own Anthropic API key (Settings → Assistant, or the ANTHROPIC_API_KEY environment variable — get one at console.anthropic.com). Usage is billed to your Anthropic account; the assistant never phones home anywhere else, and the key never leaves your machine except to call the API.

MCP server (AI integration)

Prefer driving Serpentine3D from an external agent (Claude Code, Claude Desktop)? The same modelling surface is exposed as MCP tools. Start the app, then register the server with your MCP client:

claude mcp add serpentine3d -- /path/to/.venv/bin/serp3d-mcp

Tools: serp_scene_info, serp_screenshot (returns an image of the viewport), serp_create_curve, serp_create_surface, serp_boolean, serp_transform, serp_select, serp_command (run any command with its interactive inputs), serp_layers, serp_import, serp_export, serp_measure, serp_undo, serp_viewport.

The combination of serp_screenshot and serp_command means an AI assistant can model alongside you: it sees what you see and can operate every tool the command line offers. The bridge is a localhost-only JSON-RPC socket (~/.serpentine3d/rpc.port); set SERP3D_NO_RPC=1 to disable it.

Architecture

serpentine3d/
├── core/          # kernel layer: geometry builders, tessellation,
│                  #   scene graph, layers, selection, undo history
├── commands/      # generator-based interactive commands (Rhino-style
│                  #   prompt protocol, shared by GUI + MCP)
├── ui/            # Qt: GL viewport, command line, panels, dark theme
├── fileio/        # .serp, STEP, 3DM, OBJ, FBX, STL, DXF, SVG, GLB, USD
├── scripting.py   # stable headless Document API (serp3d-batch)
├── mcp_server/    # stdio MCP server -> RPC bridge
├── api.py         # programmatic API over a running session
└── rpc.py         # localhost JSON-RPC bridge

Geometry is exact BREP on OpenCASCADE 7.9 (via the OCP pybind11 bindings); the viewport tessellates on demand with trim-aware isocurve display. Commands are Python generators that yield typed input requests — the same command code serves typed input, viewport clicks, and MCP calls.

Plugins

Drop a .py file into ~/.serpentine3d/plugins/ defining serpentine3d_plugin(ctx), or ship a package with a serpentine3d.plugins entry point — plugins register first-class commands (with prompts, osnaps, undo and MCP support for free) and menu items. See docs/scripting.md.

Development

.venv/bin/pip install -e ".[dev]"
.venv/bin/pytest            # unit tests (geometry, scene, commands, file I/O)

Keep the lights on

Serpentine3D is free and always will be. No subscription, no licence server, no "upgrade to Pro." One person builds and maintains this in the hours between other work.

If it's useful to you, a small contribution helps keep development moving: bug fixes shipped, features added, servers paid for. Not required. Never expected. But genuinely appreciated.

Bug reports, sample files and documentation fixes are worth as much and cost nothing: see CONTRIBUTING.md. Not here yet is the running list of what is missing, if you are looking for somewhere to start.

License

MIT