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set_tree_parameter

DestructiveIdempotent

Set the value of an existing StateTree root parameter and save it. Supports bool, byte, int32, int64, float, double, name, string, and text types.

Instructions

Set the value of an existing root parameter of a StateTree asset and save it. Works for bool, byte, int32, int64, float, double, name, string and text parameters; array and other types return an error. Add the parameter first with add_tree_parameter. Returns value_changed, new_value and saved.

Returns: { tree_path, parameter, set, value_changed, saved, new_value? }

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
valueYesNew value as JSON matching the parameter type: true or false, a number, or a string for name, string and text parameters.
parameterYesName of a root parameter that already exists, as listed by list_tree_parameters; an unknown name is an error.
tree_pathYesAsset path of the StateTree, e.g. "/Game/AI/ST_Guard".

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed6 schema fields changedv1.2.0
    • changedInput schema / properties / parameter / description
      Previous value: -"Parameter name (must already exist)."New value: +"Name of a root parameter that already exists, as listed by list_tree_parameters; an unknown name is an error."
    • changedInput schema / properties / tree_path / description
      Previous value: -"Asset path."New value: +"Asset path of the StateTree, e.g. \"/Game/AI/ST_Guard\"."
    • addedInput schema / properties / value / anyOf
      Added value: +[
+  {
+    "type": "string"
+  },
+  {
+    "type": "number"
+  },
+  {
+    "type": "integer"
+  },
+  {
+    "type": "boolean"
+  },
+  {
+    "type": "array"
+  },
+  {
+    "additionalProperties": true,
+    "type": "object"
+  }
+]
    • changedInput schema / properties / value / description
      Previous value: -"JSON value matching the parameter's EPropertyBagPropertyType."New value: +"New value as JSON matching the parameter type: true or false, a number, or a string for name, string and text parameters."
    • removedInput schema / properties / value / type
      Removed value: -"string"
    • changedInput schema / required
      Previous value: -[
-  "tree_path",
-  "parameter"
-]New value: +[
+  "tree_path",
+  "parameter",
+  "value"
+]
  2. First observedv1.1.0

TDQS

A4.1/5.0
Behavior4/5

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

Annotations already declare destructiveHint=true and idempotentHint=true, so the safety profile is largely covered. The description adds genuinely useful context beyond them: the call persists changes to the asset ('and save it'), the type-whitelist/error behavior, and the return fields including the conditional new_value.

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 efficient overall, but the tail is redundant: 'Returns value_changed, new_value and saved' is immediately followed by the full 'Returns: { ... }' object, repeating the same information.

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?

No output schema exists, and the description compensates by enumerating the return object fields and the error conditions. For a 3-param setter this is close to complete; only secondary details like permission or asset-lock requirements are 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 value schema already explains the JSON-to-parameter-type mapping, the 'root parameter that already exists' constraint, and the tree_path example. The description largely restates these (supported types, existing parameter), so 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 specific verb+resource+scope: 'Set the value of an existing root parameter of a StateTree asset and save it.' It is immediately distinguishable from add_tree_parameter, which it names, so an agent can route between creating and updating a parameter without opening either schema.

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?

Gives a clear prerequisite ('Add the parameter first with add_tree_parameter') and an explicit boundary condition: which types work (bool, byte, int32, int64, float, double, name, string, text) and that array/other types return an error. It does not name when to prefer other sibling setters (e.g. set_task_property), but the create-vs-update routing is covered.

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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