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Fusion360 MCP Server

Fusion360 MCP Server

by forgemorrow
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
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Draw Arc

draw_arc

Create an arc in the most recent sketch by specifying center coordinates, start point, and sweep angle. Use it to add curved sketch geometry for CAD profiles and models.

Instructions

Draw an arc in the most recent sketch (center + start point + sweep angle)

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "center_x": "<center_x>",
      "center_y": "<center_y>",
      "start_x": "<start_x>",
      "start_y": "<start_y>",
      "sweep_angle": "<sweep_angle>"
    },
    "name": "draw_arc"
  }
}

Input Schema

NameRequiredDescriptionDefault
start_xYes
start_yYes
start_zNo
center_xYes
center_yYes
center_zNo
sweep_angleYesSweep angle in degrees (positive = CCW)

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

B3.3/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations indicate this is a non-readOnly, non-idempotent, non-destructive operation, which the description doesn't contradict. However, it adds little behavioral context beyond the basic action—no mention of effects on the sketch, error conditions, or visual feedback. With annotations covering safety, the description provides minimal additional value.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, front-loaded sentence with zero waste—every word contributes to defining the tool's purpose. It's appropriately sized for a straightforward geometric operation, avoiding redundancy or fluff.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the complexity (7 parameters, low schema coverage, no output schema) and annotations, the description is incomplete. It lacks details on parameter usage, expected outcomes, or integration with the sketching workflow. For a CAD tool with multiple numeric inputs, more context is needed to guide effective use.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is low (14%), with only sweep_angle documented. The description mentions parameters generically ('center + start point + sweep angle') but adds no meaning beyond naming them—no units, coordinate system, or geometric relationships. It fails to compensate for the poor schema coverage, leaving most parameters unclear.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the specific action ('Draw an arc') and the resource ('in the most recent sketch'), with precise geometric parameters (center + start point + sweep angle). It distinguishes from sibling tools like draw_circle, draw_line, and draw_rectangle by specifying arc creation rather than other sketch primitives.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides minimal guidance, only implying usage for arc drawing in sketches. It lacks explicit when-to-use criteria, prerequisites (e.g., requires an active sketch), or alternatives (e.g., using draw_spline for curves). No exclusions or comparisons to siblings are mentioned.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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