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gpambrozio

onshape-mcp

by gpambrozio

Create an assembly

onshape_create_assembly

Create a new assembly tab in an Onshape document workspace by providing the document ID, workspace ID, and desired tab name.

Instructions

Add an assembly tab to a workspace.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
wsYesWorkspace id — the <ws> segment of the document URL.
docYesDocument id — the <doc> in cad.onshape.com/documents/<doc>/w/<ws>/e/<elem>.
nameYesTab name.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

B3.3/5.0
Behavior3/5

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

Annotations provide only a title, so the description carries the full behavioral disclosure burden. It does state the side effect: adding an assembly tab to a workspace. However, it does not disclose what happens on success, whether duplicate names are handled, failure conditions, or prerequisites for the workspace/document.

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 one efficient sentence with a clear verb, object, and target location. It is front-loaded and contains no filler or redundant restatement of the schema.

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?

For a simple creation action with fully documented parameters, the description is minimally viable. It does not mention return values, error behavior, or when this tool should be chosen over similar creation tools, so an agent gets the gist but not full operational context.

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%: all three parameters (doc, ws, name) already have descriptions. The tool description adds little parameter-level meaning beyond the schema, which matches the baseline expectation for high schema coverage.

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 description uses a specific verb and object: 'Add an assembly tab to a workspace.' It clearly identifies the operation and target resource. It does not explicitly differentiate itself from siblings like onshape_create_part_studio or onshape_create_document, but the assembly-tab scope makes the purpose reasonably unambiguous.

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 given about when to use this tool versus alternatives. It does not mention related tools such as onshape_create_part_studio, onshape_get_assembly, or onshape_insert_instance, nor does it give conditions or exclusions. The only usage signal is implied by the tool's name and the one-line description.

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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