fusion-reconstruct-mcp

by ab7646

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Python

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fusion_sketch_add_arc_three_point

Adds a three-point arc to a Fusion 360 sketch using start, end, and on-curve coordinates.

Instructions

Add a 3-point arc (start, end, point-on-arc) to a sketch, in mm.

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": {
      "sketch_id": "<sketch_id>",
      "x1": "<x1>",
      "y1": "<y1>",
      "x2": "<x2>",
      "y2": "<y2>",
      "x3": "<x3>",
      "y3": "<y3>"
    },
    "name": "fusion_sketch_add_arc_three_point"
  }
}

Input Schema

Name	Required	Description	Default
`x1`	Yes
`x2`	Yes
`x3`	Yes
`y1`	Yes
`y2`	Yes
`y3`	Yes
`sketch_id`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Aug 21, 2026

TDQS

B3.4/5.0

Behavior2/5

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

With no annotations, the description carries the full burden but only adds the unit (mm) and the point roles. It does not disclose whether the operation mutates the sketch, what happens on invalid geometry, whether the arc is constrained, or what result is returned.

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?

One sentence is front-loaded with the actionable verb and object and contains no filler or redundant restatement.

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?

For a 7-parameter mutation tool with no annotations and no output schema, the description is quite thin. It names the geometry and unit but omits coordinate system, sketch precondition, return/result behavior, and failure semantics, leaving an agent to guess important operational details.

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 0%, but the description maps the coordinate pairs to start (x1,y1), end (x2,y2), and point-on-arc (x3,y3), and states mm units. This meaningfully fills in what the bare schema omits, though per-parameter details are not fully elaborated.

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?

Clearly states a specific action (Add), target (sketch), geometry (3-point arc), and unit (mm). It explicitly defines the three points as start, end, and point-on-arc, differentiating it from sibling tools like fusion_sketch_add_line or fusion_sketch_add_circle.

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?

No guidance is provided about when to use this tool versus the available alternatives (line, rectangle, circle, etc.), nor does it mention prerequisites such as an existing sketch_id or when a different arc method would be better. The only implied context is from the tool name/description.

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