stop_water · Home Controller MCP: Risk & Policy

WHAT IT DOES

What stop_water does on Home Controller

AI agents invoke stop_water to trigger actions in Home Controller. 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 stop_water needs a policy

This tool executes a command that triggers an immediate state change in a physical system (cessation of watering/water flow). While not destructive in the sense of permanent data loss, it is an Execute-category action because it runs an external operation with real-world consequences. Severity is high because misuse could disrupt home irrigation, affect plant health, or expose water system vulnerabilities.

From the tool's definition Tool name 'stop_water' and description 'Immediately stop any active watering on the given controller' indicate triggering an external operation (stopping a water system) whose effects depend on which controller is targeted.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

stop_water Rate-limited

stop_water 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": {
    "stop_water": {
      "limits": [
        {
          "counter": "stop_water_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 Home Controller, so you can run agents against it safely.

FAQ

Questions about stop_water

What does the stop_water tool do? +

Immediately stop any active watering on the given controller. It is categorised as a Execute tool in the Home Controller MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on stop_water? +

Register the Home Controller MCP server in PolicyLayer and add a rule for stop_water: 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 Home Controller. Nothing to install.

What risk level is stop_water? +

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

Can I rate-limit stop_water? +

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

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

stop_water is provided by the Home Controller MCP server (winsthuang/home-controller). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.