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add_niagara_module_to_stack

Insert a Niagara module script into a particle emitter's spawn or update stack. Applies script-default inputs, recompiles and saves the system; stateless emitters return an error.

Instructions

Insert an engine module script into a Niagara emitter's particle stack. Loads the module UNiagaraScript and inserts it at the end of the emitter's ParticleSpawn or ParticleUpdate stack via FNiagaraStackGraphUtilities::AddScriptModuleToStack, then recompiles and saves. NOTE: only the module's script-default inputs are applied — per-instance input overrides are out of scope (the response reports added_with_defaults=true). Stateless emitters (no editable graph) return a clean error.

Returns: { system_path: string, emitter_name: string, module_script_path: string, script_group: string, module_node_name: string, added_with_defaults: bool, success: bool, saved: bool, save_error?: string }

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
system_pathYesAsset path of the Niagara System.
emitter_nameYesDisplay name of the emitter handle to modify.
script_groupNoOptional "spawn" (ParticleSpawnScript) or "update" (ParticleUpdateScript); defaults to "update"
module_script_pathYesAsset path of the module UNiagaraScript (e.g. "/Niagara/Modules/Update/Forces/GravityForce.GravityForce")

Schema Changelog

Changes observed during successful MCP inspections.

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

TDQS

A3.9/5.0
Behavior4/5

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

Annotations already establish the mutation and non-idempotence profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false). The description adds valuable behavioral detail beyond that: it recompiles and saves the asset, only script-default inputs are applied, and stateless emitters return a clean error. It does not mention permissions or other operational constraints, keeping it from a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is front-loaded with the core action, then adds implementation context and a precise limitation, followed by a compact Returns listing that compensates for the missing output schema. Every sentence carries operational value and there is no filler.

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?

For a non-read-only Niagara stack mutation with no output schema, the description covers purpose, side effects (recompile and save), scope limits (script-defaults only), error behavior (stateless emitters), and the shape of the response. Together with the complete input schema and annotations, an agent has enough information to invoke it correctly.

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 explains system_path, emitter_name, script_group, and module_script_path. The description reinforces that the module is inserted at the end of the stack and that script_group corresponds to ParticleSpawn or ParticleUpdate, but adds no syntax or format detail beyond the schema. A baseline 3 is appropriate when the schema does the heavy lifting.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a precise verb and resource: inserting an engine module script into a Niagara emitter's particle stack, specifically ParticleSpawn or ParticleUpdate. However, it does not explicitly differentiate this tool from close siblings such as add_niagara_module_to_graph or duplicate_niagara_module_in_stack.

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 description gives useful context about scope (only script-default inputs are applied, per-instance overrides are out of scope) and error behavior for stateless emitters. It does not, however, state when to choose this tool over the alternative add_niagara_module_to_graph or other stack-manipulation siblings, leaving the selection logic largely implied.

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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