Call any Home Assistant service (low-level API access) Args: domain: The domain of the service (e.g., 'light', 'switch', 'automation') service: The service to call (e.g., 'turn_on', 'turn_off', 'toggle') data: Optional data to pass to the service (e.g., {'entity_id': 'light.living_room'}) Returns...
AI agents invoke call_service_tool to trigger actions in Hass-MCP. 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.
This tool executes arbitrary Home Assistant service calls via low-level API access. While many calls are reversible (e.g., turning lights on/off), the open-ended nature allows triggering any service including automations, locks, alarms, garage doors, and other physical actuators. The blast radius is high because a misused call could unlock doors, disable security systems, or trigger dangerous automations.
From the tool's definition 'Call any Home Assistant service (low-level API access)' with arbitrary domain, service, and data parameters — examples include turn_on, turn_off, toggle across lights, switches, automations
Documented attack patterns abuse exactly the kind of access call_service_tool gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Hass-MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for call_service_tool:
{
"version": "1",
"default": "deny",
"tools": {
"call_service_tool": {
"limits": [
{
"counter": "call_service_tool_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}call_service_tool 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.
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Call any Home Assistant service (low-level API access) Args: domain: The domain of the service (e.g., 'light', 'switch', 'automation') service: The service to call (e.g., 'turn_on', 'turn_off', 'toggle') data: Optional data to pass to the service (e.g., {'entity_id': 'light.living_room'}) Returns: A dictionary with success status, the domain/service called, and the list of affected entity states returned by Home Assistant. Examples: domain='light', service='turn_on', data={'entity_id': 'light.x', 'brightness': 255} domain='automation', service='reload' domain='fan', service='set_percentage', data={'entity_id': 'fan.x', 'percentage': 50}. It is categorised as a Execute tool in the Hass-MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Hass- MCP server in PolicyLayer and add a rule for call_service_tool: 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 Hass-MCP. Nothing to install.
call_service_tool is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the call_service_tool 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.
Set action: deny in the PolicyLayer policy for call_service_tool. 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.
call_service_tool is provided by the Hass- MCP server (voska/hass-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 16 Hass-MCP tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
16 Hass-MCP tools catalogued and risk-classified — across an index of 42,500+ MCP servers.