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Blender MCP Ultra

Blender MCP Ultra

by 3bdull4h2008
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Python
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set_custom_property

Set custom properties on objects or bones to store user-defined data for rig controls, material parameters, animation drivers, or metadata.

Instructions

Set a custom property on an object or bone.

Custom properties store user-defined data — useful for rig controls, material parameters, animation drivers, or any metadata.

Args: object_name: Target object (or empty if using bone). bone_name: Target bone (with armature_name). armature_name: Armature containing the bone. property_name: Name of the custom property. value: Property value. min_value: Minimum allowed value. max_value: Maximum allowed value. description: Property description.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "set_custom_property"
  }
}

Input Schema

NameRequiredDescriptionDefault
valueNo
bone_nameNo
max_valueNo
min_valueNo
descriptionNo
object_nameNo
armature_nameNo
property_nameNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv3.0.0

TDQS

A3.6/5.0
Behavior2/5

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It explains the object-vs-bone target selection but does not state whether an existing property is overwritten, whether min/max values are enforced, what error conditions apply, or what the tool returns after setting the property.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is front-loaded with the action in the first sentence bun then gives a brief use-case rationale and a compact Args list. No filler or redundant prose; it is proportionally sized for a tool with 8 parameters.

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?

An agent can likely invoke the tool correctly because target rules and all parameter names are documented. However, the absence of an output schema, annotations, and any statement about return values or overwrite behavior leaves important gaps for a mutating operation.

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

Parameters4/5

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

Schema description coverage is 0%, and the Args section compensates by documenting all 8 parameters. It adds useful relationships, especially that bone_name is used with armature_name and object_name should be empty when targeting a bone. Some entries like 'value: Property value' are minimal, but the critical dependency semantics are present.

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 names a specific verb ('Set') and a clear resource ('custom property') with two target modes: object or bone. This distinguishes it from related siblings like get_custom_property and set_material_property without needing to open schemas.

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

Usage Guidelines3/5

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

The use-case sentence ('useful for rig controls, material parameters, animation drivers, or any metadata') implies when custom properties are useful, but it never explicitly contrasts this tool with alternatives such as get_custom_property or set_material_property. There is no when-not-to-use 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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