set_fan_speed · Home Controller MCP: Risk & Policy

WHAT IT DOES

What set_fan_speed does on Home Controller

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

WHY IT NEEDS A POLICY

Why set_fan_speed needs a policy

This tool modifies the state of a physical device (ventilation fan speed) by writing a new configuration value. It is reversible (speed can be changed back), so it falls under Write rather than Destructive or Execute. Misuse could cause discomfort or affect air quality, warranting medium severity.

From the tool's definition 'Set ventilation fan speed' — sets a specific device parameter to a new value

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_fan_speed Rate-limited

set_fan_speed 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_fan_speed": {
      "limits": [
        {
          "counter": "set_fan_speed_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 Home Controller, so you can run agents against it safely.

FAQ

Questions about set_fan_speed

What does the set_fan_speed tool do? +

Set ventilation fan speed (0=Away, 1=Low, 2=Medium, 3=High). It is categorised as a Write tool in the Home Controller 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_fan_speed? +

Register the Home Controller MCP server in PolicyLayer and add a rule for set_fan_speed: 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 set_fan_speed? +

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

Can I rate-limit set_fan_speed? +

Yes. Add a rate_limit block to the set_fan_speed 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_fan_speed completely? +

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

set_fan_speed 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.