trigger_build · Unreal Editor MCP: Risk & Policy

WHAT IT DOES

What trigger_build does on Unreal Editor

AI agents invoke trigger_build to trigger actions in Unreal Editor. 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 trigger_build needs a policy

The tool executes a build process in Unreal Engine, which is a code compilation operation with side effects (generating binaries, modifying build artifacts, potentially invoking post-build steps). While not irreversible (Destructive) or creating persistent data modifications (Write), it runs external operations whose outcome depends on the engine state and arguments.

From the tool's definition Tool description states 'Start a build' which triggers an external operation (Live Coding build or full compilation).

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

trigger_build Rate-limited

trigger_build 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": {
    "trigger_build": {
      "limits": [
        {
          "counter": "trigger_build_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 Editor, so you can run agents against it safely.

FAQ

Questions about trigger_build

What does the trigger_build tool do? +

Start a build. Default: Live Coding (requires editor running). It is categorised as a Execute tool in the Unreal Editor MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on trigger_build? +

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

What risk level is trigger_build? +

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

Can I rate-limit trigger_build? +

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

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

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