left_mouse_down · Computer Use MCP Server MCP: Risk & Policy

WHAT IT DOES

What left_mouse_down does on Computer Use MCP Server

AI agents invoke left_mouse_down to trigger actions in Computer Use MCP Server. 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 left_mouse_down needs a policy

This tool executes a desktop automation action (holding down the left mouse button) whose effects depend entirely on what is under the cursor at the time. It can trigger UI interactions, drag operations, or selections. It is reversible via left_mouse_up, so not Destructive, but it is an active execution of an external operation in the desktop environment.

From the tool's definition 'Press the left mouse button at the current cursor position and leave it held' — triggers a physical UI interaction (mouse button press) that depends on current cursor context and requires a subsequent release action

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

left_mouse_down Rate-limited

left_mouse_down 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": {
    "left_mouse_down": {
      "limits": [
        {
          "counter": "left_mouse_down_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 Computer Use MCP Server, so you can run agents against it safely.

FAQ

Questions about left_mouse_down

What does the left_mouse_down tool do? +

Press the left mouse button at the current cursor position and leave it held. Use mouse_move first to position the cursor. Call left_mouse_up to release. It is categorised as a Execute tool in the Computer Use MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on left_mouse_down? +

Register the Computer Use MCP Server MCP server in PolicyLayer and add a rule for left_mouse_down: 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 Computer Use MCP Server. Nothing to install.

What risk level is left_mouse_down? +

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

Can I rate-limit left_mouse_down? +

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

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

left_mouse_down is provided by the Computer Use MCP Server MCP server (syedazharmbnr1/computer-use-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.