left_mouse_up · Computer Use MCP Server MCP: Risk & Policy

WHAT IT DOES

What left_mouse_up does on Computer Use MCP Server

AI agents invoke left_mouse_up 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_up needs a policy

Releasing a mouse button is part of desktop automation/interaction — it triggers UI actions (completing clicks, drag-and-drop, etc.) whose effects depend entirely on what is under the cursor at the time. This is an Execute-class action as it drives external GUI operations with context-dependent outcomes.

From the tool's definition Release the left mouse button at the current cursor position. Pairs with left_mouse_down.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

left_mouse_up Rate-limited

left_mouse_up 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_up": {
      "limits": [
        {
          "counter": "left_mouse_up_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_up

What does the left_mouse_up tool do? +

Release the left mouse button at the current cursor position. Pairs with left_mouse_down. 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_up? +

Register the Computer Use MCP Server MCP server in PolicyLayer and add a rule for left_mouse_up: 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_up? +

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

Can I rate-limit left_mouse_up? +

Yes. Add a rate_limit block to the left_mouse_up 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_up completely? +

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

left_mouse_up 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.