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diverdown1964

Home Assistant MCP Server

get_entity_state

Retrieve the current state and attributes of a Home Assistant entity, such as a light or sensor, to monitor device status and conditions.

Instructions

Get the current state and attributes of a specific entity

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
entity_idYesThe entity ID (e.g., 'light.living_room')

Implementation Reference

  • The handler function for the 'get_entity_state' tool. It retrieves the state of the specified Home Assistant entity using the haClient and returns it as a formatted JSON string in the tool response.
    case "get_entity_state": {
      const entity = await haClient.getState(args?.entity_id as string);
      return {
        content: [
          {
            type: "text",
            text: JSON.stringify(entity, null, 2),
          },
        ],
      };
    }
  • Tool schema definition including name, description, and input schema for 'get_entity_state', registered in the list_tools response.
    {
      name: "get_entity_state",
      description: "Get the current state and attributes of a specific entity",
      inputSchema: {
        type: "object",
        properties: {
          entity_id: {
            type: "string",
            description: "The entity ID (e.g., 'light.living_room')",
          },
        },
        required: ["entity_id"],
      },
    },
  • Helper method in HomeAssistantClient class that performs the actual API call to retrieve the entity state from Home Assistant.
    async getState(entityId: string): Promise<HAEntity> {
      return this.fetch(`states/${entityId}`);
    }
  • TypeScript interface defining the structure of a Home Assistant entity state, used by the get_entity_state tool.
    interface HAEntity {
      entity_id: string;
      state: string;
      attributes: Record<string, any>;
      last_changed: string;
      last_updated: string;
    }
Behavior2/5

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It states the tool 'Get[s] the current state and attributes', implying a read-only operation, but doesn't specify if it requires authentication, has rate limits, or details the return format (e.g., JSON structure). This leaves significant behavioral gaps for a tool with no annotation coverage.

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

Conciseness4/5

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

The description is a single, efficient sentence that directly states the tool's purpose without unnecessary words. It is appropriately sized and front-loaded, though it could be slightly more structured by including usage hints.

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

Completeness2/5

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

Given no annotations, no output schema, and a simple single-parameter input, the description is incomplete. It doesn't explain what 'state and attributes' entail, the return format, or any error conditions, making it inadequate for full agent understanding despite the low complexity.

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

Parameters3/5

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

The input schema has 100% description coverage, fully documenting the single 'entity_id' parameter with an example. The description adds no additional parameter semantics beyond what the schema provides, so it meets the baseline of 3 for high schema coverage without compensating value.

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

Purpose4/5

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

The description clearly states the verb ('Get') and resource ('current state and attributes of a specific entity'), making the purpose understandable. However, it doesn't explicitly differentiate from sibling tools like 'list_entities' (which might list all entities vs. getting details for one), missing full sibling distinction.

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

Usage Guidelines2/5

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

The description provides no guidance on when to use this tool versus alternatives such as 'list_entities' or 'call_service'. It lacks explicit context, prerequisites, or exclusions, leaving the agent to infer usage from the tool name alone.

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

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