boot_simulator · App Screen MCP: Risk & Policy

WHAT IT DOES

What boot_simulator does on App Screen

AI agents invoke boot_simulator to trigger actions in App Screen. 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 boot_simulator needs a policy

Booting a simulator triggers an external system operation (starting a virtual device process). It has real side effects (resource consumption, state changes) but is reversible. It falls under Execute as it triggers an external operation rather than simply reading data or writing a file.

From the tool's definition Boot an iOS simulator by UDID

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

boot_simulator Rate-limited

boot_simulator 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": {
    "boot_simulator": {
      "limits": [
        {
          "counter": "boot_simulator_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 App Screen, so you can run agents against it safely.

FAQ

Questions about boot_simulator

What does the boot_simulator tool do? +

Boot an iOS simulator by UDID. It is categorised as a Execute tool in the App Screen MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on boot_simulator? +

Register the App Screen MCP server in PolicyLayer and add a rule for boot_simulator: 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 App Screen. Nothing to install.

What risk level is boot_simulator? +

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

Can I rate-limit boot_simulator? +

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

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

boot_simulator is provided by the App Screen MCP server (xmuweili/app-screen-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.