autocad-mcp-pro/CLAUDE.md

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Project Overview

AutoCAD MCP Pro is a FastMCP 3.0 server that exposes ~154 tools, 6 resources, and 5 prompt templates for AutoCAD automation. (The exact tool count is reported dynamically by system_status / system_about — never hardcode it.) It runs with a dual-engine architecture: a live COM backend (Windows/AutoCAD required) and a headless ezdxf backend (works anywhere).

Running the Server

# STDIO mode (default, for MCP clients like Claude Desktop)
python server.py

# HTTP mode
fastmcp run server.py:mcp --transport http --port 8000

# Force a specific backend
AUTOCAD_MCP_BACKEND=ezdxf python server.py   # headless file ops
AUTOCAD_MCP_BACKEND=com python server.py     # live AutoCAD (Windows only)
AUTOCAD_MCP_BACKEND=auto python server.py    # auto-detect (default)

Installation

# Core (ezdxf backend only)
pip install -e .

# With COM backend (Windows + AutoCAD)
pip install -e ".[com]"

# With PDF/screenshot support via matplotlib
pip install -e ".[pdf]"

# Everything
pip install -e ".[full]"

Running Tests

pytest
pytest tests/test_specific.py::test_name   # single test
pytest -x                                   # stop on first failure

Uses pytest-asyncio for async test support.

Architecture

Dual-Backend Pattern

The server uses a strategy pattern with an abstract base:

• backends/contracts/ — the interface, one module per domain (drawing.py, layouts.py, entity_creation.py, …). Split in v1.5.0 out of a single 1854-line ABC; some slices (premium, gdt, settings) also carry shared concrete implementations, so they are mixins rather than pure interfaces.
• backends/capability.py — the refusal vocabulary (UnsupportedCapabilityError) plus @capability(key, reason=...), which marks a contract method optional and gives it a default that raises that refusal. Use it only for genuine engine boundaries, never for an unfinished method; @abstractmethod stays the default. Every key used must be declared in both capability maps — tests/test_capability_contract.py fails otherwise, which is what stops the decorator becoming a way to ship undeclared holes.
• backends/base.py — shared dataclasses (EntityInfo, LayerInfo, BlockInfo, DrawingInfo, CapabilityMap) and the AutoCADBackend composition of every contract. Import surface is unchanged: from backends.base import AutoCADBackend, UnsupportedCapabilityError still works.
• backends/ezdxf_backend.py — EzdxfBackend: file-based DXF operations using the ezdxf library. All sync ezdxf calls are wrapped with asyncio.to_thread via _async(). Transactions are implemented as full DXF snapshots on an _undo_stack.
• backends/com_backend.py — ComBackend: live AutoCAD control via pywin32 COM. All COM calls are routed through a ThreadPoolExecutor with a single thread to satisfy AutoCAD's STA (Single-Threaded Apartment) COM requirement.

Backend selection at startup (in server.py::_make_backend):

1. Check AUTOCAD_MCP_BACKEND env var
2. On Windows with auto/com: try COM first, fall back to ezdxf
3. On non-Windows: always use ezdxf

FastMCP Server Structure (server.py)

The mcp FastMCP instance is configured with:

• Lifespan (autocad_lifespan): initializes the backend singleton; stores it in ctx.lifespan_context["backend"]
• Middleware stack: ErrorHandlingMiddleware → AuditMiddleware (custom timing/audit log) → TimingMiddleware → LoggingMiddleware
• _backend(ctx) helper: retrieves the backend from lifespan context, raises ToolError if not ready

Tools are organized into sections (counts are indicative — system_about is authoritative):

1. Drawing Management (12 tools): drawing_* (includes drawing_redo)
2. Entity Creation (14 tools): entity_create_* (includes entity_create_table, leader_create_mleader)
3. Dimensions (5 tools): dimension_*
4. Entity Modification (16 tools): entity_move/copy/rotate/scale/mirror/offset/delete/array_*, corner ops (entity_trim/extend/fillet/chamfer), plus in-place entity_edit_text (TEXT/MTEXT content/height/rotation) and entity_edit_geometry (CIRCLE/LINE/ARC — center/radius/endpoints/angles), both handle-preserving
5. Entity Query (4 tools): entity_get, entity_list, entity_delete_many, selection_get
6. Layer Management (14 tools incl. 2 linetype_*): layer_*, linetype_list, linetype_load
7. Block Operations (7 tools): block_*
8. Analysis & Query (8 tools): analysis_* — plus Batch (2), Templates (2), Validation (1)
9. View & Screenshot (4 tools — includes view_zoom_and_screenshot): view_*
10. Transactions (3 tools): transaction_begin/commit/rollback
11. System (8 tools): system_status/get_variable/set_variable/run_command/run_lisp/about/capabilities, plus drawing_settings (friendly units/scale/precision/osnap facade over system variables)
12. Engineering / Deterministic CAD (8 tools): gear_draw_*, keyway_draw_*, titleblock_apply_iso_a3, drawing_finalize
13. Premium meta-tools (12): drawing_preflight, drawing_plan, drawing_critique, drawing_refine, drawing_deliver, point_from_snap/intersection/tangent, construction_*, drawing_apply_iso_layers, dimension_auto, entity_select_smart
14. GD&T (ISO 1101 / ASME Y14.5): gd_frame (feature control frames), datum_feature — enforced by the gdt critique focus
15. Layouts & Paper Space (12 tools): tab lifecycle layout_list/create/set_current/delete/rename/copy, viewports viewport_create/list/set_scale/lock/delete, and entity_change_space (CHSPACE — tagged layout and modify, and layout wins the group priority, so it files here). drawing_export_pdf takes an optional layout param and does project model content through viewports on both engines (viewport_render — v1.4 declared this COM-only and was wrong; the headless renderer only omits the viewport borders). entity_change_space is the mirror case — ezdxf-only (chspace), because ActiveX exposes no change-space member and the COM route is unverified.
16. 3D Solids (5 tools, opt-in via ENABLE_3D=true, COM only): solid_box/cylinder/extrude/revolve/boolean — hidden from discovery and rejected while disabled; ezdxf reports solid_3d as unsupported (no headless ACIS).

Tool profiles: TOOL_PROFILE=lean|full (default full) controls the advertised surface — lean ≈ 47 curated drafting tools (including cad_batch, since a client with a tight tool cap is exactly the client paying most per turn). Applied in the lifespan; reported by system_about. The core profile was removed in v1.5.0 (the discovery layer replaced it); TOOL_PROFILE=core falls back to full with a warning.

Tool discovery: DISCOVERY_MODE=off|search (default off). search replaces the advertised catalog with search_tools + call_tool, ranking hits over an AutoCAD command / synonym corpus (discovery/aliases.py) layered on fastmcp's BM25 index.

ISO 129 tolerances: dimension_linear / dimension_radius / dimension_diameter take tol_upper / tol_lower / tol_mode (symmetric ± / deviation +a/-b / limit / basic) and text_override (e.g. ⌀20 H7). Prefer these over hand-drawn tolerance text.

ISO 286 fits: the same dimension tools take fit="H7" (mutually exclusive with tol_*) — deviations are resolved from authored ISO 286 tables (engineering/fits.py; shafts d/e/f/g/h/js/k/m/n/p, holes D/E/F/G/H/JS, sizes 1–500 mm) against the measured nominal and the fit code is appended to the dimension text.

Drawing score: drawing_finalize returns payload["score"] — a 0-100 scalar + invalidity_ratio + A-F grade over the validator + critique union. Use it as the objective quality metric.

Measuring: never read vertices back and shoelace them — that loses 28.2% of the area on a semicircular edge, silently. analysis_measure_entity(handle) reads the real geometry, and its payload states its own accuracy: exact, flatten_tolerance, assumed_closed, self_intersecting. A HATCH reports the area it fills (outer loops minus islands) plus hatch_style; on a curved hatch edge flatten_tolerance is not the accuracy knob, because ezdxf hands boundaries over as cubic Beziers whose ~0.028% circle error is already baked in. boundary_trace / boundary_from_entities report the same number analysis_measure_entity gives for the polyline they just drew — if those ever diverge, one of them is approximating and neither says so.

Benchmark matrix: benchmarks/tasks_v3.py is the current set (15 tasks; --matrix v2 reproduces the v1.4 ten). The published competitor reports are pinned v1.4 runs against v2 and are never back-filled for the five v3 tasks — the chart shows them not run, not zero. benchmarks/correctness_suite.py (26 checks) is the release A/B gate: python benchmarks/compare_versions.py v1.4.0.

Adding a New Tool

1. Add the method to the matching module in backends/contracts/ — @abstractmethod if both engines must have it, @capability("key", reason=...) only if it is a real engine boundary (and then declare key in both capability maps, or the gate fails)
2. Implement it in EzdxfBackend (backends/ezdxf_backend.py) using the _async(func) wrapper
3. Implement it in ComBackend (backends/com_backend.py) using self._com(func)
4. Register the tool in server.py with @mcp.tool(...) calling _backend(ctx).your_method(...)
5. Use _dc(result) to convert dataclass returns to dicts

Key Conventions

• Entity handles: hex strings (e.g. "1A2B"). Always returned from create/copy operations; required by all modify/query operations.
• Coordinates: drawing units (mm by default); angles in degrees, counter-clockwise from X axis. Every coordinate in or out of a tool is WCS on both engines. DXF stores CIRCLE/ARC/LWPOLYLINE/TEXT/INSERT geometry in a per-entity frame (extrusion); backends/ocs.py translates at the backend boundary, so OCS never reaches a tool. An entity in a plane tilted out of WCS XY reports plane_normal and omits the fields xy cannot express; writing an xy into such an entity is refused with capability: "ocs_tilted_plane" — use entity_move instead.
• ACI colors: 1–255 for specific colors, 256=ByLayer, 0=ByBlock.
• COM backend only: system_run_command, system_run_lisp, and view_zoom_extents/window (view ops are no-ops in ezdxf).
• Screenshot: COM uses Win32 window capture (Pillow required); ezdxf renders via matplotlib.
• _dc(obj): converts dataclasses to dicts recursively for JSON serialization.
• Engineering layer scaffold: drawing_new auto-bootstraps standard linetypes (CENTER, HIDDEN, PHANTOM) and engineering layers (GEOMETRY, DIM, CENTER, HIDDEN, PHANTOM, HATCH, TEXT, TITLEBLOCK). Pass bootstrap=False to opt out.
• Production drawings: For real engineering output, use the engineering/ package primitives via the gear_* / keyway_* / titleblock_* MCP tools — do NOT hand-draw teeth/keyways/sections with raw entity_create_* calls. Always end with drawing_finalize for the 8-step validator.

Premium Drawing Rules

These rules are non-negotiable for production engineering output.

1. Plan before draw: Call drawing_plan(intent, scale, sheet) before any entity_create_*. The returned PlanSpec is held by the backend and replayed by drawing_critique at finalize time.
2. No coordinate guessing: Never compute snap points (endpoints, midpoints, intersections, perpendicular feet) from memory. Use point_from_snap(handle, "end"|"mid"|"center"|"quad"|"perp"|"near", ref_x, ref_y).
3. Layer discipline: All geometry on engineering layers (GEOMETRY, HIDDEN, CENTER, ...). Construction geometry on CONSTRUCTION layer (color 250, lightest weight); wipe with construction_clear() before finalize.
4. Lineweights are ISO 128: 0.13/0.18/0.25/0.35/0.50/0.70/1.00/1.40/2.00 mm only. Use drawing_apply_iso_layers("mech"|"pid"|"iso13567") to bootstrap correct lineweights per layer; never set lineweight manually outside this set.
5. Corners must be explicit: Two intersecting lines that should meet at a sharp corner must use entity_trim (with keep_x/keep_y) — leaving overshoot is reported as untrimmed_corner by drawing_critique. Rounded/beveled corners use entity_fillet / entity_chamfer.
6. Dimensions via auto: Prefer dimension_auto(handles, "chain"|"baseline"| "ordinate") over individual dimension_linear calls. Manual dimensions only for special cases (leader notes, ordinate origins).
7. Critique-then-finalize: drawing_critique(focus=[...]) must return zero issues before drawing_finalize. Available focuses (closed enum): iso128, layer_color, dim_overlap, untrimmed_corner, duplicate_entities, construction_left. Pass focus=None for all.
8. Meta-tools over raw: When a meta-tool exists for a workflow, use it; do not reimplement with low-level primitives. Same rule as the engineering- primitives line above.

Standard Premium Workflow (template)

1. plan = drawing_plan(intent, sheet_size="A3", scale=1.0)
2. drawing_apply_iso_layers("mech")        # or "pid", "iso13567"
3. construction_xline(...)                 # scaffolding (optional)
4. entity_create_line / circle / ...       # main geometry on engineering layers
5. entity_trim / fillet / chamfer          # close corners explicitly
6. handles = entity_select_smart({...})    # avoid handle-memorization
7. dimension_auto(handles, style="chain")  # ISO 129 dims
8. issues = drawing_critique(focus=None)   # must be []
9. construction_clear()                    # wipe scaffolding
10. drawing_finalize(save_path=..., screenshot_path=...)