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set_niagara_decal_renderer_material

DestructiveIdempotent

Assign a material to a Decal renderer at a specific index in a Niagara System emitter and save the system. Returns previous and new material paths.

Instructions

Assign a material to the Decal renderer at renderer_index of one emitter in a Niagara System asset and save the system; a failed save returns success false. Returns the previous and new material paths and changed. For sprite, ribbon or mesh renderers use set_niagara_renderer_material.

Returns: { system_path, emitter_name, renderer_index, previous_material_path, new_material_path, changed, saved }

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
system_pathYesNiagara System asset path, e.g. "/Game/Niagara/NS_Example"; the call fails without it.
emitter_nameYesDisplay name of the emitter handle that owns the renderer (case-insensitive); the call fails without it.
material_pathYesObject path of the UMaterialInterface to assign, e.g. "/Game/Decals/M_Blood.M_Blood".
renderer_indexYes0-based index in the renderer list of the emitter, in get_niagara_emitter_renderers order; that renderer must be a Decal renderer. The call fails without it.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed5 schema fields changedv1.2.0
    • changedInput schema / properties / emitter_name / description
      Previous value: -"Name of the emitter handle."New value: +"Display name of the emitter handle that owns the renderer (case-insensitive); the call fails without it."
    • changedInput schema / properties / material_path / description
      Previous value: -"Asset path of the UMaterialInterface to assign as the decal Material."New value: +"Object path of the UMaterialInterface to assign, e.g. \"/Game/Decals/M_Blood.M_Blood\"."
    • changedInput schema / properties / renderer_index / description
      Previous value: -"Index of the Decal renderer within the emitter's renderer list."New value: +"0-based index in the renderer list of the emitter, in get_niagara_emitter_renderers order; that renderer must be a Decal renderer. The call fails without it."
    • changedInput schema / properties / system_path / description
      Previous value: -"Asset path of the Niagara System (e.g. \"/Game/Niagara/NS_Example\")."New value: +"Niagara System asset path, e.g. \"/Game/Niagara/NS_Example\"; the call fails without it."
    • changedInput schema / required
      Previous value: -[
-  "material_path"
-]New value: +[
+  "system_path",
+  "emitter_name",
+  "renderer_index",
+  "material_path"
+]
  2. First observedv1.1.0

TDQS

A4.3/5.0
Behavior4/5

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

Annotations already declare destructiveHint, idempotentHint and non-read-only. The description goes beyond them by disclosing the save semantics, that a failed save returns success=false, and the changed flag that reflects whether the assignment actually altered state (consistent with idempotentHint). It stops short of describing the replacement/destructive nature of overwriting the existing material, so not a full 5.

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 with the core action and consequence, followed by the sibling routing rule. Slightly redundant because the return fields are listed both in prose ("previous and new material paths and changed") and again in the explicit Returns block, which costs some tightness.

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?

There is no output schema, so the description usefully spells out the return shape (system_path, emitter_name, renderer_index, previous/new material paths, changed, saved) and the save/failure behavior. Combined with 100% schema coverage and the sibling routing hint, an agent has what it needs, though the destructive overwrite implication could be stated more explicitly.

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 four parameters in detail (index ordering, case-insensitivity, path formats). The description adds little beyond reiterating renderer_index, so the baseline 3 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 precise verb (Assign a material), the exact target (the Decal renderer at renderer_index of one emitter in a Niagara System asset), and the side effect of saving the system. It also differentiates from the sibling set_niagara_renderer_material by naming the renderer types that tool covers, so an agent can route without opening the schema.

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

Usage Guidelines5/5

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

Gives an explicit alternative and the condition that selects it: "For sprite, ribbon or mesh renderers use set_niagara_renderer_material." The renderer must be a Decal renderer is stated in the schema, and the description frames the tool around that decal-specific path.

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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