tap_text · App Screen MCP: Risk & Policy

WHAT IT DOES

What tap_text does on App Screen

AI agents invoke tap_text 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 tap_text needs a policy

Tapping a UI element triggers actions in the simulator that can have a wide range of effects (navigation, form submission, button presses, etc.). This is an Execute-category action because it drives external system behavior. Severity is medium because while the blast radius depends on the app context, misuse could trigger unintended in-app actions, but it is sandboxed within the simulator environment.

From the tool's definition 'Find a UI element by visible text and tap its center' — performs a tap action on the iOS Simulator UI, triggering external UI interactions whose effects depend on what element is tapped

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

tap_text Rate-limited

tap_text 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": {
    "tap_text": {
      "limits": [
        {
          "counter": "tap_text_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 tap_text

What does the tap_text tool do? +

Find a UI element by visible text and tap its center. 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 tap_text? +

Register the App Screen MCP server in PolicyLayer and add a rule for tap_text: 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 tap_text? +

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

Can I rate-limit tap_text? +

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

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

tap_text 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.