open_app · MacWright MCP: Risk & Policy

WHAT IT DOES

What open_app does on MacWright

AI agents invoke open_app to trigger actions in MacWright. 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 open_app needs a policy

Opening/launching an application triggers an external process execution on the host system. While not destructive by itself, it can have broad side effects depending on which application is launched, making it an Execute-category action with medium severity.

From the tool's definition Launch or activate a macOS application by name

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

open_app Rate-limited

open_app 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": {
    "open_app": {
      "limits": [
        {
          "counter": "open_app_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 MacWright, so you can run agents against it safely.

FAQ

Questions about open_app

What does the open_app tool do? +

Launch or activate a macOS application by name. If already running, it will be brought to the foreground. It is categorised as a Execute tool in the MacWright MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on open_app? +

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

What risk level is open_app? +

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

Can I rate-limit open_app? +

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

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

open_app is provided by the MacWright MCP server (ruchit-p/macwright). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.