add_material_expression

A write tool on the Unreal- MCP server.

SERVERUnreal-MCP SOURCEaadeshrao123/unreal-mcp

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/aadeshrao123-unreal-mcp/add-material-expression.md

WHAT IT DOES

What add_material_expression does on Unreal-MCP

AI agents use add_material_expression to create or update resources in Unreal-MCP, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Unreal-MCP environment.

RISK

Why add_material_expression is rated Medium

This tool creates or modifies material expressions in Unreal Engine, which is a reversible operation (expressions can be deleted or replaced). It does not execute arbitrary code, delete data irreversibly, or move money. The 'add' prefix and material domain context indicate Write category.

From the tool's definition Tool name is 'add_material_expression' which indicates creation/addition of a material expression node in Unreal Engine materials. Sibling tools like 'add_blueprint_node', 'add_component_to_blueprint', 'add_data_table_row' are all additive/creation operations.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs add_material_expression safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Unreal-MCP, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For add_material_expression, this is the rule to start with:

add_material_expression Rate-limited

add_material_expression stays usable, but capped: an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "add_material_expression": {
      "limits": [
        {
          "counter": "add_material_expression_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Unreal-MCP, apply this rule, and every add_material_expression call is checked against it from then on.

FAQ

Questions about add_material_expression

What does the add_material_expression tool do? +

add_material_expression is a write tool on the Unreal MCP server. It is categorised as a Write tool in the Unreal-MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on add_material_expression? +

Register the Unreal MCP server in PolicyLayer and add a rule for add_material_expression: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Unreal-MCP. Nothing to install.

What risk level is add_material_expression? +

add_material_expression is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit add_material_expression? +

Yes. Add a rate_limit block to the add_material_expression rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block add_material_expression completely? +

Set action: deny in the PolicyLayer policy for add_material_expression. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides add_material_expression? +

add_material_expression is provided by the Unreal MCP server (aadeshrao123/unreal-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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