0.2.2
on PyPI
MCP server · Rhinoceros 3D · v0.2.2
golem-3dmcp
Gives an AI agent read and write access to a running Rhino 8 session over the Model Context Protocol, through 89 named tools.
pip install golem-3dmcp
89
tools on the bridge
245
tests, run before publish
MIT
license
What it is
golem-3dmcp implements the Model Context Protocol so an agent can drive Rhino 8 directly — create geometry, run booleans, drive Grasshopper, capture viewports, and execute Python inside the application. It works with any MCP-compatible host.
Specification
| Property | Value |
|---|---|
| Protocol | Model Context Protocol (stdio and Docker) |
| Host application | Rhinoceros 3D 8.x, with a plug-in on the application side |
| Tools | 89, counted from the live registry |
| Wire format | 4-byte big-endian length prefix, UTF-8, JSON object body, 64 MB ceiling |
| Python | 3.10 and above on the server side; the embedded interpreter is stdlib-only |
| Dependencies | mcp[cli] >=1.0.0,<2 — every runtime dependency capped at the next major |
| Tests | 245, run before publish |
| License | MIT |
Recorded session
A recorded terminal session for this package is pending. The demo that exists is the generated city — a full Rhino scene built end to end by an agent through these tools: roads, towers, houses, trees, a stadium, a bridge, a harbour and the wind turbines behind it. Nothing stands in for a recording here until one is captured against the published release.
How it works
The bridge has two halves that cannot share code: a modern Python server, and a plug-in living inside the application's embedded interpreter that can install nothing.
The bridge
Two halves, one wire contract
The embedded half cannot install a dependency, so the contract between them is the thing that is kept identical.
Wire
The protocol module is vendored twice on purpose
Once for modern Python, once for the application's stdlib-only embedded interpreter. A shared compatibility shim would have had to satisfy modern lint and type rules on both sides; instead each copy pins the same wire contract and the lint config excludes the old-dialect half by path.
4-byte big-endian length | UTF-8 | JSON body ceiling: 64 MB
Framing
A reply is matched to its request
Every response id is compared with the id of the request it answers. A mismatch raises RhinoProtocolError and closes the connection, instead of returning another command's result as if it were this one's.
if resp["id"] != req_id:
raise RhinoProtocolError(...)Timeout
A timed-out command cannot desynchronise the next one
The socket is closed and the connection marked disconnected, so a late reply is never read by the following command. The next command reconnects.
tests/test_connection_desync.py # regression tests against a fake plug-in
Release
What the last release fixed
The 0.2.2 changelog, because a version number on its own says nothing.
Pin
An unbounded dependency shipped a release the server could not import
mcp 2.0.0 removed mcp.server.fastmcp, which the server imports, so an unbounded requirement broke a fresh install from both pip and the Docker image. Every runtime dependency is now capped at the next major.
mcp[cli] >= 1.0.0, < 2
Build
The Docker image reports its real version
The workflow passes the tag as a build argument the Dockerfile turns into the version. Previously every image built without a git directory reported 0.0.0.
SETUPTOOLS_SCM_PRETEND_VERSION=${VERSION}Limits
What this does not do, and where it should not be trusted. These stay on the page whatever else changes.
Rhino 8 is required, and so is the plug-in on the application side. The package is a bridge; it does not model anything on its own and there is no headless mode.
Tool calls execute inside your running Rhino session with your permissions — including a tool that runs arbitrary Python. Point it only at hosts and prompts you trust.
The two halves of the wire module are vendored copies. They are kept identical by review and by the pinned contract, not by a shared import, so a change has to be made twice.
The published Docker image and the PyPI package track the same tag, but hosted CI runs are unavailable on this account: the release was built and uploaded by hand, and the scheduled dependency matrix is a file waiting for a runner.
Links
Defects in this package are issues in its own repository.
Author approval — 2026-08-23, hash c85a22c4