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set_rigvm_pin_default

DestructiveIdempotent

Sets a pin's default value in a Control Rig Blueprint's RigVM graph, compiles and saves it. Verify with set, pin_found, and current_value.

Instructions

Set the default value of a pin in the main RigVM graph of a Control Rig Blueprint (URigVMController::SetPinDefaultValue, no undo entry), then compile and save it. success reflects the save even when the write failed: check set, pin_found and current_value, which is read back.

Returns: { asset_path: string, pin_path: string, value: string, set: bool, pin_found: bool, current_value: string, saved: bool, save_error: string }

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
forceNoOptional. This command is REFUSED while a Play-in-Editor session is running: it either compiles a Blueprint (the reinstancer can retain a world, and CheckForWorldGCLeaks is Fatal -- it KILLS the editor) or writes to disk (Editor.AllowSavingAssetsDuringPIE=0 makes the engine refuse the write, so it would report success without writing a byte). Stop PIE and retry instead; force=true runs it anyway, at your own risk.
valueYesValue in UE export-text form, e.g. "true", "1.0" or "(X=0.0,Y=0.0,Z=1.0)"; array pins are resized to the given element count.
pin_pathYesPin path NodeName.PinName, e.g. SetTransform.bInitial
control_rig_pathYesAsset path of the UControlRigBlueprint, e.g. "/Game/Rigs/CR_Mannequin".

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv1.2.0
    • changedInput schema / properties / control_rig_path / description
      Previous value: -"Path to the UControlRigBlueprint asset"New value: +"Asset path of the UControlRigBlueprint, e.g. \"/Game/Rigs/CR_Mannequin\"."
    • changedInput schema / properties / value / description
      Previous value: -"UE export-text form of the value, e.g. true or 1.0"New value: +"Value in UE export-text form, e.g. \"true\", \"1.0\" or \"(X=0.0,Y=0.0,Z=1.0)\"; array pins are resized to the given element count."
  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?

Adds substantial behavior beyond the annotations: no undo entry is created, the graph is compiled and saved afterward, and success reflects the save even if the write failed. It directs the agent to check set, pin_found, current_value, saved, and save_error, which is critical operational context consistent with destructiveHint=true and readOnlyHint=false.

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 first sentence front-loads the purpose, scope, and side effects, followed by the key caveat about save reporting and the explicit return fields. The Returns list is lengthy but justified because no output schema exists, keeping the overall structure efficient.

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?

With no output schema, the description supplies the return object fields and the important ambiguity between write success and save success. Together with the exhaustive parameter schema and annotations, this gives an agent enough to call the tool correctly, though explicit alternative-tool routing is absent.

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%, and the schema already documents all four parameters with detailed semantics, including the PIE refusal behavior for force and UE export-text format for value. The description adds no parameter-specific details beyond the schema, so the baseline 3 for high coverage 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?

States a specific verb and resource: setting a pin default in the main RigVM graph of a Control Rig Blueprint, with the underlying URigVMController API named. This distinguishes it from the sibling set_pin_default_value by explicitly scoping it to RigVM/Control Rig rather than generic Blueprint graphs.

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?

Usage is implied by the scope: use this for RigVM graph pins in Control Rig Blueprints, not ordinary Blueprint graph pins. However, the description does not explicitly name alternatives such as set_pin_default_value or state when-not to use this tool, leaving some routing inference to the agent.

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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