kernelCAD

Fetch Part

fetch_part

Read-onlyIdempotent

Fetch one bundled catalog part. Prefer await lib.standard.nema17() and await lib.standard.bearing608() — they are offline and do not download remote STEP. A lookup that cannot finish fails within 45s with errorCode parts.lookup.timeout. Do not retry in parallel.

Input Schema

Name	Required	Description
`id`	No
`model`	No	Verified model options; supplying model implies includeModel.
`query`	No
`family`	No
`category`	No
`standard`	No
`includeModel`	No	Resolve a hash-verified STEP/GLB model file instead of the plain catalog STEP record.
`partsBaseUrl`	No	Opt-in remote endpoint; no default value ships with kernelCAD.

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 24, 2026

addedInput schema / properties / includeModel

Added value: +{
+  "description": "Resolve a hash-verified STEP/GLB model file instead of the plain catalog STEP record.",
+  "type": "boolean"
+}

addedInput schema / properties / model

Added value: +{
+  "description": "Verified model options; supplying model implies includeModel.",
+  "properties": {
+    "attribution": {
+      "type": "string"
+    },
+    "expectedBboxMm": {
+      "description": "Expected [x,y,z] dimensions to compare with the measured model.",
+      "items": {
+        "type": "number"
+      },
+      "maxItems": 3,
+      "minItems": 3,
+      "type": "array"
+    },
+    "license": {
+      "description": "License string supplied by the source.",
+      "type": "string"
+    },
+    "sha256": {
+      "description": "Required SHA-256 digest for an explicit URL; for catalog parts it overrides the catalog GLB digest.",
+      "type": "string"
+    },
+    "source": {
+      "description": "Catalog or manufacturer name, such as KiCad Packages3D.",
+      "type": "string"
+    },
+    "toleranceRatio": {
+      "description": "Relative expected-versus-measured bbox tolerance, default 0.25.",
+      "type": "number"
+    },
+    "url": {
+      "description": "Direct public HTTPS .step/.stp/.glb download URL. Requires sha256, source and license.",
+      "type": "string"
+    }
+  },
+  "type": "object"
+}

Changed2 schema fields changedOct 11, 2026

removedOutput schema / properties

Removed value: -{
-  "cachePath": {
-    "description": "Local cache path of the written STEP file (success).",
-    "type": "string"
-  },
-  "disclosure": {
-    "description": "Referral disclosure. Present only when url carries a referral tag; show it with the link.",
-    "type": "string"
-  },
-  "error": {
-    "type": "string"
-  },
-  "errorCode": {
-    "type": "string"
-  },
-  "errorHint": {
-    "type": "string"
-  },
-  "instruction": {
-    "description": "What to do with the link_out URL.",
-    "type": "string"
-  },
-  "kind": {
-    "description": "'link_out' when the URL is a vendor configurator the agent must drive by hand.",
-    "type": "string"
-  },
-  "ok": {
-    "type": "boolean"
-  },
-  "record": {
-    "additionalProperties": true,
-    "description": "Resolved part record (success).",
-    "type": "object"
-  },
-  "sha256": {
-    "description": "SHA-256 fingerprint of the STEP file (success).",
-    "type": "string"
-  },
-  "source": {
-    "description": "Where the part came from ('local' | 'remote') (success).",
-    "type": "string"
-  },
-  "url": {
-    "description": "Outbound vendor URL (link_out). May carry a referral tag; see disclosure.",
-    "type": "string"
-  }
-}

removedOutput schema / required
```
Removed value: -[
-  "ok"
-]
```

Changed4 schema fields changedSep 28, 2026

addedOutput schema / properties / disclosure

Added value: +{
+  "description": "Referral disclosure. Present only when url carries a referral tag; show it with the link.",
+  "type": "string"
+}

addedOutput schema / properties / instruction

Added value: +{
+  "description": "What to do with the link_out URL.",
+  "type": "string"
+}

addedOutput schema / properties / kind

Added value: +{
+  "description": "'link_out' when the URL is a vendor configurator the agent must drive by hand.",
+  "type": "string"
+}

addedOutput schema / properties / url

Added value: +{
+  "description": "Outbound vendor URL (link_out). May carry a referral tag; see disclosure.",
+  "type": "string"
+}

Changed1 schema field changedJun 15, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "properties": {
+    "cachePath": {
+      "description": "Local cache path of the written STEP file (success).",
+      "type": "string"
+    },
+    "error": {
+      "type": "string"
+    },
+    "errorCode": {
+      "type": "string"
+    },
+    "errorHint": {
+      "type": "string"
+    },
+    "ok": {
+      "type": "boolean"
+    },
+    "record": {
+      "additionalProperties": true,
+      "description": "Resolved part record (success).",
+      "type": "object"
+    },
+    "sha256": {
+      "description": "SHA-256 fingerprint of the STEP file (success).",
+      "type": "string"
+    },
+    "source": {
+      "description": "Where the part came from ('local' | 'remote') (success).",
+      "type": "string"
+    }
+  },
+  "required": [
+    "ok"
+  ],
+  "type": "object"
+}

AddedJun 8, 2026

TDQS

A3.7/5.0

Behavior4/5

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

Beyond the annotations, the description discloses important behavior: remote STEP download implications, a 45-second timeout with errorCode parts.lookup.timeout, and the instruction not to retry in parallel. It does not describe authentication or return structure, but the output schema already covers returns.

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 short, front-loaded with the purpose, and every sentence adds useful operational guidance: offline preference, timeout/error code, and retry constraint. There is no filler or repetition.

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

Completeness3/5

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

With 8 parameters, nested model options, and only 38% schema coverage, the description leaves meaningful gaps around how to choose between id/query/family/category/standard. Annotations and the output schema reduce the burden, and the timeout/retry guidance helps, but the definition is only minimally complete for correct invocation.

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 only 38%, and several top-level parameters such as id, query, family, category, and standard have no descriptions. The description adds little parameter-level meaning beyond saying it fetches one bundled catalog part, so it does not compensate for the coverage gap.

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

Purpose4/5

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

The first sentence gives a specific verb and resource: "Fetch one bundled catalog part." It is clearly a retrieval tool, but it does not explicitly distinguish itself from siblings such as find_part or import_step, so it stops short of a 5.

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?

The description explicitly prefers `await lib.standard.nema17()` and `await lib.standard.bearing608()` for common standard parts because they are offline and avoid remote STEP downloads. It also gives a concrete retry prohibition, but it does not explain when to use this tool instead of sibling part tools like find_part.

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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