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OwlCAD

by com.owlcad.mcp
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See the model

render
Read-onlyIdempotent

Render the model to PNG images you can actually look at, from one or more named views. Use this to CHECK your work — a tree that evaluates cleanly can still be the wrong shape, and this is the only way to notice. Flat-shaded diagnostic render, not a marketing shot.

Input Schema

NameRequiredDescriptionDefault
scadNoOpenSCAD source, as an alternative to `nodes` (supply exactly one). Interpreted by the same engine the editor’s .scad import uses; BOSL2/MCAD includes resolve. minkowski() and resize() are not supported here — use hull() or offset().
sizeNoSquare image size in px (default 512, max 1024).
nodesNoParametric node tree. mm, Z-up, rotations in DEGREES (a rotation.* binding: radians). Read owlcad://schema/primitives for every primitive, modifier and generator and its parameter ranges (unknown params are dropped silently), and owlcad://schema/conventions for the placement arithmetic, which is where most models go wrong.
viewsNoViews to render (default ["iso"]). Up to 4.
projectIdNoId of one of your saved projects, as an alternative to `nodes`/`scad` (supply exactly one).
azimuthDegNoLook from a specific angle instead of a named view: degrees around the model, 0 = the front view, increasing towards the right. Use with `elevationDeg`; ignores `views`.
smoothnessNoCurve quality for shapes that left their segment count automatic. Defaults to "standard", which is the editor default — pass "high" to match a project authored at high smoothness, "draft" for a cheaper check.
elevationDegNoHeight of the camera in degrees above the horizontal (−90 to 90). Use with `azimuthDeg`.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • changedInput schema / properties / nodes / items / properties / generatorKey / description
      Previous value: -"Generator to expand (kind=generator). PREFER one over hand-building the same thing — they carry standards dimensions and solve fits a tree of primitives gets subtly wrong: gearTrain · planetary · rackPinion · wormDrive · herringbone · herringboneTrain · pulley · bearing · belt · spring · adapter · boardMount · enclosure · gridfinity · threadedJar · pinHinge · snapFit · ballSocket · fastener · textPlate · fitCoupon · calibrationBlock · clamp · impeller · axialFan · fanFrame · plugCap · pillowBlock."New value: +"Generator to expand (kind=generator). PREFER one over hand-building the same thing — they carry standards dimensions and solve fits a tree of primitives gets subtly wrong: gearTrain · planetary · rackPinion · wormDrive · bevelPair · herringbone · herringboneTrain · pulley · bearing · belt · spring · adapter · boardMount · enclosure · gridfinity · threadedJar · pinHinge · snapFit · ballSocket · fastener · textPlate · fitCoupon · calibrationBlock · clamp · impeller · axialFan · fanFrame · plugCap · pillowBlock."
  2. Changed1 schema field changed
    • changedInput schema / properties / nodes / description
      Previous value: -"Parametric node tree. mm, Z-up, rotations in DEGREES. Read owlcad://schema/primitives for every primitive, modifier and generator and its parameter ranges (unknown params are dropped silently), and owlcad://schema/conventions for the placement arithmetic, which is where most models go wrong."New value: +"Parametric node tree. mm, Z-up, rotations in DEGREES (a rotation.* binding: radians). Read owlcad://schema/primitives for every primitive, modifier and generator and its parameter ranges (unknown params are dropped silently), and owlcad://schema/conventions for the placement arithmetic, which is where most models go wrong."
  3. Changed1 schema field changed
    • changedInput schema / properties / nodes / items / properties / generatorKey / description
      Previous value: -"Generator to expand (kind=generator). PREFER one over hand-building the same thing — they carry standards dimensions and solve fits a tree of primitives gets subtly wrong: gearTrain · planetary · rackPinion · wormDrive · herringbone · herringboneTrain · pulley · bearing · belt · spring · adapter · boardMount · enclosure · gridfinity · threadedJar · pinHinge · snapFit · ballSocket · fastener · textPlate · fitCoupon · calibrationBlock · clamp · impeller · axialFan · fanFrame · plugCap."New value: +"Generator to expand (kind=generator). PREFER one over hand-building the same thing — they carry standards dimensions and solve fits a tree of primitives gets subtly wrong: gearTrain · planetary · rackPinion · wormDrive · herringbone · herringboneTrain · pulley · bearing · belt · spring · adapter · boardMount · enclosure · gridfinity · threadedJar · pinHinge · snapFit · ballSocket · fastener · textPlate · fitCoupon · calibrationBlock · clamp · impeller · axialFan · fanFrame · plugCap · pillowBlock."
  4. Changed1 schema field changed
    • changedInput schema / properties / scad / description
      Previous value: -"OpenSCAD source, as an alternative to `nodes` (supply exactly one). Interpreted by the same engine the editor’s .scad import uses. minkowski() and resize() are not supported here — use hull() or offset()."New value: +"OpenSCAD source, as an alternative to `nodes` (supply exactly one). Interpreted by the same engine the editor’s .scad import uses; BOSL2/MCAD includes resolve. minkowski() and resize() are not supported here — use hull() or offset()."
  5. First observed

TDQS

A4.2/5.0
Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered and the bar is lower. The description still adds real context: the output is a "flat-shaded diagnostic render, not a marketing shot," which sets expectation about visual fidelity, and it flags that this is the sole means of catching shape errors that validation misses.

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 action and output format, then the use case, then a clarifying caveat about render style. Nothing is padded and every sentence carries distinct information.

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 an 8-parameter render tool with no output schema, the description covers purpose, when to invoke, and the nature of the returned image well enough to call it correctly. It does not describe the return payload shape (e.g. inline image vs URL) or multi-view result ordering, a minor gap given no output schema exists.

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

Parameters3/5

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

Schema description coverage is 100%, so the schema already documents all 8 parameters thoroughly (views, size, scad/nodes/projectId exclusivity, azimuth/elevation pairing). The description only adds "one or more named views," which the schema's `views` field already conveys, so no meaningful uplift beyond the baseline.

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?

States a specific verb and resource ("Render the model to PNG images") plus the scope ("from one or more named views"), so the agent knows exactly what it produces. It also implicitly separates itself from the `evaluate` sibling by contrasting a tree that "evaluates cleanly" with one that "can still be the wrong shape."

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

Usage Guidelines4/5

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

Gives a clear use condition — check visual correctness after the tree evaluates — and frames itself as "the only way to notice" shape errors, which routes the agent here rather than to evaluate. It stops short of explicitly naming alternatives or stating when NOT to call it (e.g. for interference checks vs `check_interference`).

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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