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UEAgent

by CarlxsMG
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add_virtual_bone

Create a virtual bone in a USkeleton asset by linking a source bone to a target bone and saving. Returns the virtual bone name and count.

Instructions

Add a virtual bone from a source bone to a target bone of a USkeleton asset, named "VB _" by the engine, then save. Bone names are not checked against the skeleton; an existing pair returns that bone with already_exists true. Returns virtual_bone_name and virtual_bone_count.

Returns: { asset_path: string, virtual_bone_name: string, source_bone: string, target_bone: string, virtual_bone_count: int, saved: bool, already_exists: bool }

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
source_boneNoBone the virtual bone starts from (default the first bone, usually the root); not validated.
target_boneNoBone the virtual bone points to (default the first bone that differs from source_bone); not validated.
skeleton_pathYesUSkeleton asset path, e.g. "/Game/Characters/SK_Hero_Skeleton".

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changedv1.2.0
    • changedInput schema / properties / skeleton_path / description
      Previous value: -"Path to the USkeleton asset"New value: +"USkeleton asset path, e.g. \"/Game/Characters/SK_Hero_Skeleton\"."
    • changedInput schema / properties / source_bone / description
      Previous value: -"Source bone name, defaults to first bone"New value: +"Bone the virtual bone starts from (default the first bone, usually the root); not validated."
    • changedInput schema / properties / target_bone / description
      Previous value: -"Target bone name, defaults to first different bone"New value: +"Bone the virtual bone points to (default the first bone that differs from source_bone); not validated."
  2. First observedv1.1.0

TDQS

A4.1/5.0
Behavior5/5

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

Goes well past the annotations: it discloses the auto-generated name ('VB <source>_<target>'), that bone names are not validated, that duplicate pairs return the existing bone with already_exists true, and that the asset is saved. This is exactly the extra behavioral context annotations cannot convey. Note the mild tension with idempotentHint=false, since the duplicate path implies no new state change.

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?

Front-loaded and compact, with the key behavior (naming, non-validation, dedupe) stated up front. Slight redundancy: it previews return fields in prose and then repeats them in a full 'Returns:' block, but since no output schema exists the latter earns its place.

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?

For a mutation tool with no output schema, it covers persistence, naming, validation behavior, and the full return shape. It does not address asset load/dirty state or permission requirements, but nothing essential for correct invocation is missing.

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 the schema already documents all three parameters including defaults and the 'not validated' caveat. The description adds little parameter-specific detail beyond what the schema provides; baseline 3 applies.

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?

States a specific verb (add), resource (virtual bone), and target (a USkeleton asset), plus the engine's naming convention. It is clearly distinguishable from nearby siblings like add_bone/add_rig_bone by specifying the virtual-bone concept and the source->target semantics.

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 context of use is implied (attach a virtual bone to a skeleton) and the already-exists path is described, but there is no explicit when-to-use / when-not-to-use guidance and no routing to alternatives such as add_bone, add_rig_bone, or remove_virtual_bone.

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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