Atlas / MCP servers / pzfreo / Build123d

Build123dBLOCK

Name: Build123d
Author: pzfreo

mcp/pzfreo/build123d

MCP server by pzfreo · ai tools · build123d · cad · Audited 2026-10-08

⚑ Report / re-scan Source ↗

MCP server for build123d to improve AI cognition when creating 3D CAD models

Verdict

BLOCK

Grade

Trust score

46 /100

Exposed tools

44 30r · 12w · 2d

Transport

stdio · streamable-http

License

Apache-2.0

Stars

110

Overview

From the repository's own README, as read at the audited commit. Badges and raw HTML are left out.

[](https://pypi.org/project/build123d-mcp/) [](https://pepy.tech/project/build123d-mcp) [](https://pypi.org/project/build123d-mcp/) [](https://github.com/pzfreo/build123d-mcp/actions/workflows/ci.yml) [](LICENSE) [](https://registry.modelcontextprotocol.io/v0/servers?search=build123d) [](https://glama.ai/mcp/servers/pzfreo/build123d-mcp)

[](https://insiders.vscode.dev/redirect/mcp/install?name=build123d-mcp&config=%7B%22command%22%3A%22uv%22%2C%22args%22%3A%5B%22tool%22%2C%22run%22%2C%22--python%22%2C%223.12%22%2C%22build123d-mcp%40latest%22%5D%7D) [](https://cursor.com/en/install-mcp?name=build123d-mcp&config=eyJjb21tYW5kIjoidXYiLCJhcmdzIjpbInRvb2wiLCJydW4iLCItLXB5dGhvbiIsIjMuMTIiLCJidWlsZDEyM2QtbWNwQGxhdGVzdCJdfQ==)

Give your AI CAD eyes.

build123d-mcp is not a standalone chatbot or CAD program. It is a CAD toolbox that an AI/LLM app can use through MCP.

With an LLM app such as Claude, Cursor, VS Code, Continue, Cline, or Codex CLI, build123d-mcp lets the assistant create build123d CAD models, render previews, measure geometry, fix mistakes, and export files such as STEP, STL, SVG, and DXF. Instead of writing a whole CAD script blindly, the assistant can build a part in small steps and check the result as it goes.

On the public [CADGenBench](h

Read from source at commit de8e6242de54OBSERVED · 2026-10-08

Connect

Built from this server's own package name, version and transport as found in its source — not copied from anyone's documentation, so it cannot drift against a page we do not control.

claude-code (pypi)

claude mcp add build123d-mcp -- None build123d-mcp==0.3.91

Exposed tools (44)

30 read · 12 write · 2 destructive. Blast radius: 2 tools can delete or overwrite — an agent that can be talked into calling a tool can be talked into calling this one.

Tool	Risk	Description
`analyze_printability`	read	Analyse a build123d shape for FDM printability using augura (BREP-exact analysis).
`bank_candidate`	read	Atomically promote a gate-clean STEP as the safe output/checkpoint. Writes the candidate to a private sibling file, runs the authoritative written-and-reimported STEP gate, and replaces filename only on a fully verified PASS; on FAIL or an unchecked mesh gate, the candidate is deleted and any existi
`compare`	read	Unified comparison tool.
`crop_drawing`	write	Save one model-selected raster drawing region at readable scale. bbox_px is exact source-image [x0,y0,x1,y1]; scale is 0.25..12. Returns the saved PNG path and an exact crop-pixel→source-pixel transform, so coordinates read from the enlargement remain usable. This is a mechanical crop only: it perfo
`cross_sections`	read	Compute cross-sectional areas at evenly spaced planes along an axis. Returns a list of {position, area} pairs. axis: X, Y, or Z (default Z). num_slices: number of planes (default 10, minimum 2). Useful for detecting internal voids, wall-thickness variation, or verifying that a shape
`design_audit`	read	Audit the current session program as a design, not just a shape: surface its named numeric parameters (Θ) and test how robust each is to editing. Parses the assembled program (see script()) for top-level numeric assignments (e.g. `plate_thickness = 5.0`), then rebuilds the program with each parame
`destroy_session`	destructive	Close THIS client
`edit_feature`	write	Transactionally resize one plain cylindrical through hole identified by a current @feature handle. Reject holes with counterbores, spotfaces, countersinks or multiple constituent faces. Predict the annular volume change, then check exact added/removed material, hole recognition, every other hole and
`execute`	write	Execute build123d Python code in the persistent session. Errors include automatic fix hints — read them before retrying. Use show(shape, name) to register named objects (name defaults to
`execute_file`	write	Execute a canonical build123d .py file in a clean namespace and atomically promote its result. The prior active model is restored if the source has a syntax/runtime error, times out, produces no shape, or does not produce result_name. Assign a Shape to `result` or call show(); optionally set result_
`export`	read	Export model. format: step, stl, 3mf, dxf, svg, or comma-separated list e.g.
`find_bored_bosses`	write	Find candidate bored bosses and report target-selection/edit evidence: bore opening location, axis into the part, outward axis, bore diameter/depth, planar cap faces at the opening, whether the cap is split across multiple faces, and construction advice. Use this before lengthening any boss that car
`find_bosses`	read	Recognise external cylindrical bosses on a session object (defaults to current shape), including a turned part
`find_candidates`	read	List recognised instances of a hole, boss, polygonal boss, slot, chamfer or fillet. qualifiers is JSON with optional axis (X/Y/Z), side (+X/-X/+Y/-Y/+Z/-Z, relative to the part bounding-box centre), and value_field; matches are reported for the literal axes and grouped over all 24 proper rotations o
`find_countersinks`	read	Recognise countersinks (conical screw-head recesses) on a session object (defaults to current shape) — the feature find_holes reports only as a plain opening. A countersink is an internal cone flaring from a drilled bore out to a larger opening, coaxial with the drill; drill-point cones and external
`find_hole_patterns`	read	Recognise hole patterns on a session object (defaults to current shape): ≥3 identical-spec holes equally spaced on a circle → bolt_circle (center, diameter/BCD), collinear at constant pitch → linear_array (pitch, direction). Returns JSON: {count, patterns: [{type, holes: [HoleFeature records], cente
`find_holes`	read	Recognise drilled holes on a session object (defaults to current shape). Coaxial internal cylinders are grouped into one record per hole: drill + counterbore + spotface stacks, keyway-split bores, and bores interrupted by crossing holes all count once. Returns JSON: {count, holes: [{axis (drilling d
`health_check`	read	Verify that render and export dependencies are working. Tests PNG render (VTK), SVG render (build123d HLR), STEP export, and STL export with a trivial shape. Returns JSON with ok/error per capability. Run at session start if you suspect a missing dependency.
`import_cad_file`	write	Import a STEP (.step/.stp), STL (.stl), or 3MF (.3mf) file as a named object in the session. path: absolute or relative path to the file. name: name to register the shape under (defaults to the filename stem). The shape becomes both the named object and the current_shape. A multi-object 3MF register
`inspect_part`	read	Return one compact generation-checkpoint inventory: bbox, solid/topology counts, holes grouped by axis/diameter/depth/bottom, bosses grouped by axis/diameter/height, recognised patterns with member counts, and a cross-section area profile. expected is an optional JSON object derived from the drawing
`install_skill`	write	Copy a b123d workflow skill into the current project.
`interface_features`	read	Suggest planar mounting faces from recognised hole openings, with exact hole handles. These are geometric candidates, not a declaration of design intent. Pass chosen hole handles as protected_refs to edit_feature(); that edit also checks every other recognised hole and the outer envelope.
`last_error`	write	Return details of the last failed execute() call: exception type, message, and (for runtime and syntax errors) line number and a 5-line excerpt around the failing line. Security errors include a message but no line/excerpt. Returns {\
`list_sessions`	read	Report how many CAD sessions this server process is holding, its configured limit, and how long each has been idle. Handles are secrets and are never returned. Operator/diagnostic tool for HTTP deployments — over stdio there is always exactly one session.
`load_part`	read	Load a named part from the library into the session. name: part name from search_library. params: optional JSON object of parameter overrides e.g.
`locate_gate_defects`	read	Report WHERE a solid fails the validity gate, with 3D coordinates — so you can fix the exact edge/face instead of guessing. validate()/export() tell you WHAT is wrong (e.g.
`measure`	read	Measure a shape and return a complete geometric summary: volume (mm3), surface area (mm2), topology (face/edge/vertex counts), bounding box with per-axis size and center, volumetric center of mass, 6-component inertia tensor (Ixx/Iyy/Izz/Ixy/Ixz/Iyz), and a face-type inventory classifying every face
`mesh_holes`	read	Find fastener holes in a MESH by slicing it on all three axes. Returns JSON {count, holes:[{axis, diameter, location, span, depth, through}]} where axis is the drilling direction and location is the hole centre in world coordinates. This is the mesh counterpart to find_holes(), which needs real topo
`mesh_section`	read	Loops on one cross-section plane of a mesh, largest first. Returns JSON {axis, position, loop_count, enclosed_passages, loops:[{points, center, size, min, max, enclosed}]}, all in the two axes that are not `axis`. enclosed_passages counts loops at odd nesting depth, representing passages through mat
`prepare_drawing`	read	Prepare a raster engineering drawing for efficient inspection. Detects substantial spatial regions, saves one labelled overview plus readable PNG crops, and returns their pixel bounding boxes and paths. Region ids are layout evidence only: this tool does NOT label views, recognise CAD features, inte
`recognise_features`	write	Run the shared quiddity inventory once and return exact, run-local edit evidence. With families=
`render_view`	read	Render model. Auto-detects 3D vs 2D: solids use VTK; flat drawings use the 2D pipeline. Renders confirm appearance, not geometry. format: png, svg, dxf, or both. direction accepts top, bottom, front, rear, side, left, right, or iso. quality: preview, standard, or high; a timed-out standard/high PNG
`repair_advice`	write	Return structured, field-proven repair/edit recipes for an agent to implement explicitly in execute(). Unlike repair_hints(), which gives short error-specific tips, this emits a sequenced plan with code-pattern names, acceptance checks, and stop conditions. Provide the full validate()/export()/last_
`repair_hints`	read	Given an error message or validity-gate reason, return targeted fix suggestions for common build123d mistakes and gate failures: wrong Location syntax, missing .part, CadQuery idioms, blocked imports, degenerate boolean results, fillet edge selection, B-rep defects, mesh non-manifold/open-edge failu
`reset`	destructive	Clear the current session back to empty state, including all snapshots.
`resolve`	read	Evaluate a selector expression against a named object and return a geometry descriptor. selector is a Python expression suffix applied to the object, e.g.
`restore_snapshot`	read	Restore geometric state from a previously saved snapshot (current_shape and the show() registry).
`save_snapshot`	write	Save a named checkpoint of the current geometric state (current_shape and the show() object registry).
`script`	read	Return a single Python script assembled from all successfully executed code blocks in this session. Prepends
`search_library`	read	Search the part library. query: keywords matched against name, description, tags, category (empty returns all). Returns name, category, description, tags, and full parameter specs including types, defaults, and descriptions.
`session_state`	read	Return a structured JSON snapshot of the current session: current_shape metrics, all named objects (replaces list_objects) with geometry stats, snapshot names, and a variables summary of the Python namespace (type + volume for shapes, type + length for collections, type + value for scalars). Use thi
`validate`	read	Check whether a shape would pass a CAD validity gate before exporting it. Returns a PASS/FAIL verdict plus JSON (passes_gate, n_solids, volume, is_manifold, brep_valid, reasons). The gate mirrors what strict CAD and mesh consumers require: a well-formed (BRepCheck), watertight, manifold solid with n
`version`	read	Return the installed versions of the build123d-mcp server, its key dependencies (build123d, build123d-drafting-helpers), and the companion packages importable inside execute() (bd_warehouse for threads/fasteners/gears/bearings, augura for printability analysis). Use this to confirm which server buil
`workflow_hints`	write	Return guidance on how to use these tools effectively. Call this at the start of a session or whenever unsure which tool to reach for.

Trust audit

BLOCKgrade F · trust 46/100 Do not install this without reading the findings. The audit found something that could harm you or your machine.

Layer	What it checks	Result
L0	Provenance & inventory	WARN
L1	Static analysis of the code	FAIL
L2	Instruction surface (what it tells the agent)	FAIL
L3	Class-specific surface	WARN
L4	Behavioural (sandbox)	SKIPPED

What the source does

Filesystem: declared (5 observation(s))
Network: none-observed
Shell: declared (7 observation(s))
Dependencies: pinned
Secrets in source: none-found

Findings (25)

CRITICALPrompt injection · prompt.transfer_instruction · CWE-94, CWE-1427

<tool:list_sessions>:1

Report how many CAD sessions this server process is holding, its configured limit, and how long each has been idle. Handles are secrets and are never returned. Operator/diagnostic tool for HTTP deploy

Why it matters. an instruction to move sensitive data to an outside destination

Fix. remove; a skill never needs the user's secrets off the machine

HIGHCode injection · code.deserialize · CWE-78, CWE-94, CWE-95

src/build123d_mcp/_vtk_render_subprocess_worker.py:22

args = pickle.load(f)

Why it matters. deserialises untrusted bytes into live objects

Fix. use json or yaml.safe_load

HIGHCode injection · code.deserialize · CWE-78, CWE-94, CWE-95

src/build123d_mcp/tools/render.py:506

result = pickle.load(f)

Why it matters. deserialises untrusted bytes into live objects

Fix. use json or yaml.safe_load

HIGHCode injection · code.eval_exec · CWE-78, CWE-94, CWE-95

src/build123d_mcp/session.py:806

exec(compiled, self.namespace)  # noqa: S102

Why it matters. evaluates text as code

Fix. remove; use a parser or a dispatch table

HIGHCode injection · code.eval_exec · CWE-78, CWE-94, CWE-95

src/build123d_mcp/tools/library.py:160

exec(compile(source, entry["path"], "exec"), namespace)  # noqa: S102

Why it matters. evaluates text as code

Fix. remove; use a parser or a dispatch table

HIGHCode injection · code.eval_exec · CWE-78, CWE-94, CWE-95

src/build123d_mcp/tools/resolve.py:234

result = eval(expression, namespace)  # noqa: S307

Why it matters. evaluates text as code

Fix. remove; use a parser or a dispatch table

MEDIUMInventory / provenance · inv.binary · CWE-1104

.coverage

.coverage

Why it matters. a compiled or binary member cannot be reviewed from source

Fix. ship source, or explain the binary in the README

MEDIUMInventory / provenance · inv.symlink · CWE-1104

.claude/skills/b123d-drawing/SKILL.md

.claude/skills/b123d-drawing/SKILL.md

Why it matters. link not followed

MEDIUMCode injection · code.dynamic_import · CWE-78, CWE-94, CWE-95

src/build123d_mcp/bd_warehouse_resource.py:158

m = importlib.import_module(mod_name)

MEDIUMCode injection · code.dynamic_import · CWE-78, CWE-94, CWE-95

src/build123d_mcp/worker.py:277

fn = getattr(importlib.import_module(module_name), func_name)

MEDIUMFilesystem / path · mcp.destructive_tools · CWE-22, CWE-59

destroy_session, reset

Why it matters. 2 tool(s) can delete or overwrite

Fix. prefer a read-only mode or scoped tokens; the page states the blast radius

LOWInventory / provenance · inv.hidden_file · CWE-1104

.coverage

.coverage

Why it matters. hidden member outside the usual dotfiles

Fix. review its purpose

LOWCode injection · code.dynamic_import · CWE-78, CWE-94, CWE-95

tests/test_worker_boundary_coverage.py:76

fn = getattr(importlib.import_module(module_name), func_name)