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Blender MCP Ultra

Blender MCP Ultra

by 3bdull4h2008
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
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add_bone_constraint

Constrain a bone's motion by applying a constraint type (track to, copy location, IK) with a target object in Blender.

Instructions

Add a constraint to a bone.

Args: armature_name: Target armature. bone_name: Bone to constrain. constraint_type: TRACK_TO, COPY_LOCATION, COPY_ROTATION, IK, etc. target_name: Target object for the constraint.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "armature_name": "<armature_name>",
      "bone_name": "<bone_name>"
    },
    "name": "add_bone_constraint"
  }
}

Input Schema

NameRequiredDescriptionDefault
bone_nameYes
target_nameNo
armature_nameYes
constraint_typeNoTRACK_TO

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv3.0.0

TDQS

B3/5.0
Behavior2/5

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

No annotations are provided, so the description carries full behavioral burden. It only states the action itself, without disclosing whether constraints are appended or replace existing ones, whether pose mode is required, or what happens with invalid or missing target_name.

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 a short, front-loaded docstring with a one-line purpose followed by a clear argument list. No wasted words, though it could be slightly more structured.

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

Completeness2/5

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

For a 4-parameter tool with no annotations and no output schema, the description omits critical operational details: when target_name is required, whether it operates on edit/pose bones, and how existing constraints are affected. An agent is likely to call it incorrectly without additional context.

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 description compensates by explaining each parameter: armature_name, bone_name, constraint_type with examples, and target_name. It does not explain defaults or conditional requirements, but the basic semantics are supplied.

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?

Clear verb+resource: 'Add a constraint to a bone.' The name and description distinguish it from sibling add_object_constraint by explicitly mentioning bone. However, it does not contrast with other bone-related siblings like setup_ik_chain.

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 on when to use this tool versus alternatives, no prerequisites (e.g., armature existence), and no hint that target_name is conditionally required for certain constraint types.

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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