set_ui_element_value · Mac MCP: Risk & Policy

WHAT IT DOES

What set_ui_element_value does on Mac

AI agents use set_ui_element_value to create or update resources in Mac — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Mac environment.

WHY IT NEEDS A POLICY

Why set_ui_element_value needs a policy

This tool creates or modifies data/state through UI interaction. It is Write-category because changes are generally reversible (text can be re-edited, sliders moved again). Severity is high because an AI agent could modify sensitive application settings, form fields containing credentials, financial data, or system preferences.

From the tool's definition Tool modifies UI element values including text fields and sliders. Description explicitly states it 'Sets the value of an editable UI element.' This performs reversible modification of application state.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_ui_element_value Rate-limited

set_ui_element_value stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "set_ui_element_value": {
      "limits": [
        {
          "counter": "set_ui_element_value_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Mac, so you can run agents against it safely.

FAQ

Questions about set_ui_element_value

What does the set_ui_element_value tool do? +

Sets the value of an editable UI element (text fields, sliders, etc.). It is categorised as a Write tool in the Mac MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on set_ui_element_value? +

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

What risk level is set_ui_element_value? +

set_ui_element_value is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit set_ui_element_value? +

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

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

set_ui_element_value is provided by the Mac MCP server (laststance/mac-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.