hass-mcp

call_service_tool

Invoke any Home Assistant service by providing domain, service, and optional data to control devices and automations.

Instructions

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}

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "domain": "<domain>",
      "service": "<service>"
    },
    "name": "call_service_tool"
  }
}

Input Schema

Name	Required	Description	Default
`data`	No
`domain`	Yes
`service`	Yes

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Aug 21, 2026

TDQS

A3.8/5.0

Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

There are no annotations, so the description must carry the full burden of behavioral disclosure. It mentions 'low-level API access' but does not disclose potential side effects, permissions, reversibility, or error handling. Given the generic nature of the tool, this is insufficient transparency.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is concise and well-structured with clear sections (Args, Returns, Examples). It avoids unnecessary verbosity while providing essential usage information, making it easy to parse.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a generic service-call tool, the description provides sufficient context: what the tool does, how to use parameters, what to expect in the return value, and clear examples. It does not cover edge cases or failure modes, but given the broad scope ('any service'), the level of detail is adequate.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The description explains each parameter (domain, service, data) with examples, adding meaning beyond the bare schema (which only has titles). It clarifies how to structure the data dictionary, though it does not exhaustively list allowed service names or data fields, which is reasonable for a generic tool.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the purpose: 'Call any Home Assistant service (low-level API access)'. It identifies the verb (call) and the resource (Home Assistant service), and distinguishes itself from sibling tools that are more specific (e.g., list, get, update).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides examples of usage but does not explicitly state when to use this tool versus more specific sibling tools. It implies it is a catch-all for services without dedicated tools, but this is not explicitly stated, leaving some ambiguity.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.