set_mode · Home Controller MCP: Risk & Policy

WHAT IT DOES

What set_mode does on Home Controller

AI agents use set_mode 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_mode needs a policy

This tool modifies device configuration by changing the water heater's operating mode. While reversible (modes can be changed back), it affects critical home infrastructure and could impact comfort, energy consumption, and system behavior.

From the tool's definition Tool name 'set_mode' and description 'Change the water heater operation mode' indicate modification of device configuration state. The verb 'Change' is explicit, and operation mode is a reversible state adjustment.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_mode Rate-limited

set_mode 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_mode": {
      "limits": [
        {
          "counter": "set_mode_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_mode

What does the set_mode tool do? +

Change the water heater operation mode. 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_mode? +

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

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

Can I rate-limit set_mode? +

Yes. Add a rate_limit block to the set_mode 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_mode completely? +

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

set_mode 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.

// THE FULL RECORD

set_mode is one line of Home Controller's registry record.

The record carries the whole server: verified identity, auth posture, risk grade, every tool classified, recommended policy — re-checked continuously.

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