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onshape-mcp

by gpambrozio

Download the element thumbnail

onshape_get_thumbnail

Fetch the saved thumbnail of an Onshape document element and write it to a PNG file, letting you specify size and output location.

Instructions

Save Onshape's stored thumbnail. Thumbnails are generated asynchronously and lag edits — prefer onshape_shaded_view to see the current state.

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>.
outNoOutput PNG path (default onshape-thumb-<timestamp>.png).
elemYesElement id (tab) — the <elem> segment of the document URL.
sizeNoThumbnail size, e.g. "600x340" or "300x300" (default 600x340).
return_imageNoAlso return the PNG inline (default true).

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4.2/5.0
Behavior3/5

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

The description discloses an important behavioral trait: thumbnails are generated asynchronously and can lag behind edits. However, annotations provide no behavioral hints, and the description does not clarify side effects such as writing a file to disk, returning an image, or whether the operation is read-only.

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?

Two short sentences with no filler. The core purpose is front-loaded, and the caveat plus alternative is delivered immediately after.

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?

The critical caveat about stale thumbnails and the pointer to onshape_shaded_view are present, and the schema fully documents parameters. A minor gap is that return/save behavior is not explicitly described, but the schema's out and return_image fields partially cover this.

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 parameters are already well documented. The tool description adds no parameter-specific meaning, so the baseline score of 3 is appropriate.

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?

The description states a specific action and resource: saving Onshape's stored thumbnail. It also distinguishes this tool from onshape_shaded_view by noting that shaded_view shows current state, so the agent can tell which tool serves which need.

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

Usage Guidelines5/5

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

It explicitly names onshape_shaded_view as the preferred alternative when current state is needed, which tells the agent when not to use this tool. That is clear, actionable usage guidance.

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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