build_target · Unreal MCP: Risk & Policy

WHAT IT DOES

What build_target does on Unreal

AI agents invoke build_target to trigger actions in Unreal. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why build_target needs a policy

This tool triggers compilation of C++ code via UnrealBuildTool, which is a code execution operation. While not destructive (compilation doesn't delete data) and not immediately dangerous like shell execution, it executes external processes whose effects depend on the build target and project state.

From the tool's definition Tool description states 'Build a C++ target using UnrealBuildTool. Compiles the project' - this directly executes the UnrealBuildTool to compile C++ code, which is an external operation with side effects (produces build artifacts, modifies project state).

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

build_target Rate-limited

build_target stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "build_target": {
      "limits": [
        {
          "counter": "build_target_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

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 build_target

What does the build_target tool do? +

Build a C++ target using UnrealBuildTool. Compiles the project. It is categorised as a Execute tool in the Unreal MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on build_target? +

Register the Unreal MCP server in PolicyLayer and add a rule for build_target: 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 build_target? +

build_target is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit build_target? +

Yes. Add a rate_limit block to the build_target 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 build_target completely? +

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

build_target 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.