add_blueprint_variable · Unreal MCP: Risk & Policy

WHAT IT DOES

What add_blueprint_variable does on Unreal

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

WHY IT NEEDS A POLICY

Why add_blueprint_variable needs a policy

Adding a Blueprint variable is a reversible write operation that modifies game project source code. It creates new data in the Blueprint system but can be undone (removed). The severity is medium because while it modifies project assets, the impact is scoped to a single Blueprint and the modification is non-destructive and reversible.

From the tool's definition Tool is named 'add_blueprint_variable' and described as 'Add a variable to a Blueprint.' This creates a new variable definition in Blueprint source code, modifying the Blueprint structure.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

add_blueprint_variable Rate-limited

add_blueprint_variable 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_blueprint_variable": {
      "limits": [
        {
          "counter": "add_blueprint_variable_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Unreal, so you can run agents against it safely.

FAQ

Questions about add_blueprint_variable

What does the add_blueprint_variable tool do? +

Add a variable to a Blueprint. It is categorised as a Write tool in the Unreal 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_blueprint_variable? +

Register the Unreal MCP server in PolicyLayer and add a rule for add_blueprint_variable: 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. Nothing to install.

What risk level is add_blueprint_variable? +

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

Can I rate-limit add_blueprint_variable? +

Yes. Add a rate_limit block to the add_blueprint_variable 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_blueprint_variable completely? +

Set action: deny in the PolicyLayer policy for add_blueprint_variable. 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_blueprint_variable? +

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