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aadeshrao123

Unreal-MCP

by aadeshrao123

spawn_actor_by_class

Spawn any AActor subclass in Unreal Engine by providing its class path, blueprint asset path, or short name. Supports undo via EditorActorSubsystem.

Instructions

Spawn ANY AActor subclass by full path, short name, or Blueprint asset path.

Replaces the hardcoded whitelist of spawn_actor. Resolves class_path in this order:

  1. Full UClass path with '.' (e.g. "/Script/Engine.PostProcessVolume", "/Script/Engine.SkyAtmosphere")

  2. Blueprint asset path (e.g. "/Game/Blueprints/BP_Miner") — loads the asset and uses its GeneratedClass.

  3. Short name fallback — iterates loaded UClasses for a name match (handles "PostProcessVolume", "APostProcessVolume", "Sky_Sphere_C", etc.)

Validates: must be AActor subclass, not abstract, not deprecated. Uses UEditorActorSubsystem::SpawnActorFromClass when available so Ctrl+Z restores.

Args: class_path: Full path, BP asset path, or short class name. name: Optional outliner label + UObject name. location: [x, y, z] world location. rotation: [pitch, yaw, roll] degrees. scale: [x, y, z] scale.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
nameNo
scaleNo
locationNo
rotationNo
class_pathYes

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes
Behavior5/5

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

With no annotations, the description fully handles behavioral disclosure. It explains the resolution order, validation conditions (must be AActor subclass, not abstract, not deprecated), that it loads assets, iterates classes, and uses UEditorActorSubsystem for Undo support. This is comprehensive.

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 longer but well-structured: purpose, resolution order, validation, then parameters. It could be slightly more concise, but every sentence adds value. Front-loading with the main purpose is effective.

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

Completeness5/5

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

Given the complexity (5 parameters, no annotations, output schema exists), the description covers all necessary aspects: what the tool does, parameter semantics, validation, and even Undo support. The output schema is present, so return values need not be explained.

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

Parameters5/5

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

The schema coverage is 0%, so the description carries the full burden. The 'Args' section provides clear, detailed explanations for each parameter: class_path (with examples), name, location, rotation, and scale. This adds significant meaning beyond the schema.

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 clearly states the tool 'Spawn ANY AActor subclass by full path, short name, or Blueprint asset path.' It distinguishes itself from the sibling tool 'spawn_actor' by mentioning it 'Replaces the hardcoded whitelist of spawn_actor.' The verb is specific and the resource is well-defined.

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

Usage Guidelines4/5

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

The description explains when to use this tool (for spawning any actor subclass) and mentions it replaces spawn_actor. It provides the resolution order for class_path, which guides usage. However, it does not explicitly state when not to use it or compare to other sibling tools beyond spawn_actor.

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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