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set_niagara_module_input

DestructiveIdempotent

Override a Niagara module input value by writing to the rapid-iteration store, then recompile and save the system. Supports float, int, vector, and color inputs.

Instructions

Override a Niagara module input by writing the rapid-iteration store. Locates the module function-call node (by its module_node_name, as returned by add_niagara_module_to_stack) on the emitter's spawn or update stack, matches the input by its leaf name, and writes the value into the owning group script's RapidIterationParameters store. The system is recompiled and saved. HONEST GATE: bool / enum / data-interface / object inputs are not rapid-iteration eligible and return a clean error ("override of inputs requires the linked-value path, not supported headless"). The packed value_type must also match the input's actual type or a clean error is returned.

Returns: { system_path: string, emitter_name: string, module_node_name: string, input_name: string, value_type: string, ri_param_name: string, verified: bool, success: bool, saved: bool, save_error?: string }

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
valueNoFor float/int: scalar number. For vector: an [x, y, z] list. For color: an [r, g, b, a] list.
input_nameYesLeaf name of the module input (e.g. "Drag" for "Module.Drag").
value_typeNoOne of "float", "int", "vector", or "color"; defaults to "float"
system_pathYesAsset path of the Niagara System (e.g. "/Game/Niagara/NS_Example").
emitter_nameYesDisplay name of the emitter handle.
module_node_nameYesThe module function-call node name (from add_niagara_module_to_stack's module_node_name).

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv1.2.0
    • changedInput schema / required
      Previous value: -[
-  "emitter_name",
-  "module_node_name",
-  "input_name"
-]New value: +[
+  "system_path",
+  "emitter_name",
+  "module_node_name",
+  "input_name"
+]
  2. First observedv1.1.0

TDQS

A4.6/5.0
Behavior5/5

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

Beyond the annotations (readOnlyHint=false, destructiveHint=true, idempotentHint=true), the description discloses that the system is recompiled and saved after the write — a substantial side effect — and enumerates the exact error conditions (ineligible input types, value_type mismatch). This is exactly the kind of behavioral context structured fields cannot convey.

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 action, then mechanism, then failure gate, then returns. It is on the longer side and slightly dense, but every sentence carries operational weight with no filler. The Returns block is warranted given there is no output schema.

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?

With no output schema, the description supplies the return shape, and for a 6-parameter destructive mutation tool it covers the write path, the safety gate, the type-matching constraint, and the recompile/save side effect. Nothing an agent needs to call it correctly is missing.

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 coverage is 100%, so the baseline is 3, but the description adds real meaning: module_node_name's provenance from add_niagara_module_to_stack, input_name being a leaf name, and the value_type-must-match rule. These connections go beyond the per-property schema text.

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 opens with a specific verb+resource ("Override a Niagara module input") and immediately names the mechanism (writing the rapid-iteration store), distinguishing it from the getter sibling get_niagara_module_input. It also delineates the unsupported linked-value path, so an agent knows exactly what class of operation this is.

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?

It gives clear context for use: locate the node via module_node_name from add_niagara_module_to_stack and the input by leaf name. The 'HONEST GATE' block explicitly states which input types (bool/enum/data-interface/object) will fail and why, which is strong negative guidance. It stops short of an explicit when-to-prefer-this-over-alternatives comparison against other setters, keeping it at 4.

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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