wait_for_function · MacWright MCP: Risk & Policy

WHAT IT DOES

What wait_for_function does on MacWright

AI agents invoke wait_for_function 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 wait_for_function needs a policy

This tool executes JavaScript expressions within Safari, enabling arbitrary code execution in the browser. Although the immediate effects depend on what JavaScript is evaluated, the tool itself is designed to run code with side effects (polling and waiting).

From the tool's definition Tool description states 'Poll a JavaScript expression in Safari until it returns a truthy value' — directly executes arbitrary JavaScript code in the browser context.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

wait_for_function Rate-limited

wait_for_function 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": {
    "wait_for_function": {
      "limits": [
        {
          "counter": "wait_for_function_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 wait_for_function

What does the wait_for_function tool do? +

Poll a JavaScript expression in Safari until it returns a truthy value, or until timeout. The most flexible wait tool — use when wait_for_element and wait_for_text don. 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 wait_for_function? +

Register the MacWright MCP server in PolicyLayer and add a rule for wait_for_function: 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 wait_for_function? +

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

Can I rate-limit wait_for_function? +

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

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

wait_for_function 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.