call_service · Homeassistant MCP: Risk & Policy

WHAT IT DOES

What call_service does on Homeassistant

AI agents invoke call_service to trigger actions in Homeassistant. 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 call_service needs a policy

In Home Assistant, 'call_service' is the fundamental mechanism for triggering any action — turning lights on/off, locking doors, running scripts, activating alarms, etc. This constitutes executing external operations with real-world physical effects.

From the tool's definition Tool name 'call_service' on a Home Assistant MCP server that 'Enables AI assistants to control Home Assistant devices and services'

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

call_service Rate-limited

call_service 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": {
    "call_service": {
      "limits": [
        {
          "counter": "call_service_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 Homeassistant, so you can run agents against it safely.

FAQ

Questions about call_service

What does the call_service tool do? +

call_service. It is categorised as a Execute tool in the Homeassistant MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on call_service? +

Register the Homeassistant MCP server in PolicyLayer and add a rule for call_service: 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 Homeassistant. Nothing to install.

What risk level is call_service? +

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

Can I rate-limit call_service? +

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

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

call_service is provided by the Homeassistant MCP server (robbrad/homeassistant-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.