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Fusion360 Live MCP

Fusion360 Live MCP

by tbrito88
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Hybrid

Draw Spline

draw_spline

Create a spline in the active Fusion 360 sketch using fit points for a curve through points or control points for a control-polygon spline.

Instructions

Draw a spline in the most recent sketch. Use fit_points for a curve through points, or control_points for a control-polygon spline. Unless a parameter says otherwise, lengths and coordinates are in cm (not mm) and angles in degrees.

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": {
      "spline_type": "<spline_type>",
      "points": "<points>"
    },
    "name": "draw_spline"
  }
}

Input Schema

NameRequiredDescriptionDefault
degreeNoSpline degree (only for control_points, 3 or 5)
pointsYesArray of [x,y] or [x,y,z] points
spline_typeYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4.2/5.0
Behavior4/5

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

Annotations already declare readOnlyHint=false, idempotentHint=false, and destructiveHint=false, covering the safety profile. The description adds valuable behavioral context beyond annotations: it specifies that the spline is drawn in the most recent sketch and that lengths/coordinates default to cm and angles to degrees, which is essential for correct invocation.

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?

Three sentences, front-loaded with the primary action and context, followed by parameter guidance and then unit defaults. Every sentence adds necessary information with zero waste.

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

Completeness4/5

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

For a simple drawing tool with three parameters and no output schema, the description covers the essential context: action, target sketch, spline type semantics, and units. It does not state whether a sketch must already exist or what happens if none is active, but those gaps are minor given the tool's scope and the annotations.

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

Parameters4/5

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

Schema coverage is 67% (degree and points documented; spline_type enum lacks a description). The description compensates by explaining the meaning of the two spline_type enum values and by adding unit context (cm, degrees) for coordinate values, which the schema does not provide. The degree parameter is already covered, so this is not a full 5.

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 states a specific verb (draw) and resource (spline) plus the context (most recent sketch), making it immediately distinguishable from sibling drawing tools like draw_line or draw_arc. No ambiguity remains about what the tool does.

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

Usage Guidelines3/5

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

The description gives clear guidance for choosing between the two spline_type values (fit_points vs control_points), but it does not explicitly say when to use draw_spline over alternatives such as draw_arc or create_polygon. Usage is only implied by the tool's name and the prerequisite of an active sketch.

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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