create_cad_loon

create_cad_loon is an alternative to create_cad_document that accepts geometry as Loon source code. Loon is a compact Lisp-like language designed for parametric CAD, and it is often more concise than the JSON format -- especially for models with many chained operations. The tool evaluates the Loon source through the WASM kernel and returns an IR document.

Input Schema

Return Value

The tool returns a text response containing the IR document in the requested format. The returned document can be passed to inspect_cad, export_cad, or open_in_browser, just like the output of create_cad_document.

If the Loon source has a syntax error or references an undefined variable, the tool returns an error message describing the problem and the line where it occurred.

Examples

Simple Plate with Hole

{
  "source": "[let plate [cube 50 30 5]]\n[let hole [translate 25 15 0 [cylinder 3 10]]]\n[let result [difference plate hole]]\n[root result \"aluminum\"]"
}

Pipe Chaining

{
  "source": "[pipe\n  [cube 50 50 30]\n  [fillet 3]\n  [shell 2]\n  [translate -25 -25 0]]\n[root _ \"abs-white\"]"
}

The pipe form passes the result of each expression as the last argument to the next, avoiding deep nesting.

Flange with Bolt Circle

{
  "source": "[let disc [cylinder 25 5]]\n[let holes [circular-pattern 0 0 0 0 0 1 6 360 [cylinder 3 10]]]\n[let flange [difference disc [translate 0 0 -1 holes]]]\n[root flange \"steel\"]"
}

Extruded L-Bracket

{
  "source": "[let profile [sketch xy [line 0 0 30 0] [line 30 0 30 5] [line 5 5 5 20] [line 5 20 0 20] [line 0 20 0 0] end]]\n[let bracket [extrude 0 0 15 profile]]\n[root bracket \"aluminum\"]"
}

Multi-Part Scene

{
  "source": "[let base [cube 100 100 10]]\n[let pillar [translate 40 40 10 [cylinder 10 50]]]\n[root base \"steel\"]\n[root pillar \"aluminum\"]"
}

Multiple root directives create a multi-part scene where each root gets its own material assignment.

When to Use Loon vs. JSON

Loon is a good choice when the model involves heavy operation chaining (the pipe form eliminates nesting), when the model is defined by a series of named let-bindings, or when token budget is tight. JSON (create_cad_document) is better when you need structured hole placement with the at position system, assembly definitions with typed joints, or when generating the input programmatically from code.

Both tools produce the same IR format and can be mixed in a workflow -- use create_cad_loon to build geometry, then pass the result to inspect_cad or export_cad.

Error Handling

If the Loon source is invalid, the tool returns an error response:

{
  "content": [{"type": "text", "text": "Error: Unknown variable 'plat' at line 3 (did you mean 'plate'?)"}],
  "isError": true
}

Common errors include undefined variables (typos in let binding names), mismatched brackets, wrong argument counts for opcodes, and attempting to boolean a 2D sketch without extruding it first.

For the complete Loon language specification, see Loon Syntax. For a tutorial on using Loon with AI agents, see Loon for AI.