HA Synapse 🧠

HA Synapse is a Model Context Protocol (MCP) server designed to act as a bridge between LLM coding agents (such as Antigravity, Claude Code, Cursor, or Codex) and your Home Assistant instance(s).

Rather than executing ad-hoc API scripts, HA Synapse provides a standardized set of MCP tools and resources. This allows AI agents to read and modify configuration files safely, call services, dry-run templates, query history, and debug automation traces dynamically.

Note: This was largely developed with agentic coding.

Related MCP server: Home Assistant MCP Server

Architecture: Where does HA Synapse live?

HA Synapse runs on the local machine where the coding agent executes (e.g., your laptop or development desktop).

graph TD
    subgraph Local Developer Machine
        Agent[LLM Coding Agent] <-->|MCP Protocol / stdio| Synapse[HA Synapse MCP Server]
    end
    subgraph Smart Home
        Synapse <-->|HTTP REST & WebSockets| HAAPI[Home Assistant API]
        Synapse <-->|SSH / SFTP Commands| HAFS[Home Assistant File System]
    end

It communicates over the network with one or more Home Assistant instances:

1. REST & WebSockets: Used for real-time state caching, service execution, template rendering, history, and automation traces.

2. SSH Connection: Used to read/write configuration files (like configuration.yaml or packages) directly inside the /config or /homeassistant folders without requiring custom HACS components on the Home Assistant side.

Key Features

1. Multi-Instance Support: Manage multiple Home Assistant installations (e.g., home and office) from a single MCP server.

2. Real-time State Caching: Maintains an active WebSocket connection to keep an in-memory copy of all entity states, preventing context bloat and rate-limiting.

3. Atomic Writes & Safety Guard:

   • Checks YAML syntax locally.

   • Backs up files in .mcp_backups/ before modifying them.

   • Runs Home Assistant's configuration validation check after writing.

   • Automatically rolls back to the original file if validation fails, preventing your smart home from locking up.

4. Jinja2 Template Testing: Exposes a template rendering tool, letting the AI verify calculation outcomes before deploying them in automations.

5. Automation Tracing: Exposes execution traces to let the AI see exactly which condition failed in a broken automation.

Installation & Setup

We provide a Guided Setup Wizard to make installation as simple as possible for both technical and non-technical users.

1. Prerequisite

• Home Assistant Long-Lived Access Token:

  • Open your Home Assistant UI, click on your profile name (bottom left), go to the Security tab, scroll to the bottom, and click Create Token. Save this token.

2. Run the Setup Wizard

Clone the repository, install dependencies, and run the interactive setup tool:

npm install
npm run build
npm run setup

The guided wizard will walk you through setting up your connection and offers to:

1. Auto-Provision SSH/SFTP (HA OS & Supervised): Automatically generate a secure SSH key pair locally, install the official "Terminal & SSH" add-on on your Home Assistant OS, configure it with the public key, expose port 22, and start it.

2. Auto-Install HACS: Automatically download and install the Home Assistant Community Store (HACS) over the new SSH link.

3. Manual Fallback: Let you input manual SSH details or local folders if running a containerized/Core Home Assistant instance.

4. Configure Backups: Toggle whether the server keeps persistent timestamped backups of edited files.

Once finished, the wizard will save your configuration to ~/.ha-synapse.json and output the exact configuration block ready to paste into your Claude Desktop, Cursor, or coding agent settings.

Manual Configuration (Optional)

If you prefer to configure the server manually, create a .ha-synapse.json file in your home directory (e.g. C:\Users\<username>\.ha-synapse.json or ~/.ha-synapse.json):

{
  "defaultInstance": "home",
  "instances": {
    "home": {
      "url": "http://10.0.2.52:8123",
      "token": "YOUR_LONG_LIVED_ACCESS_TOKEN",
      "mode": "ssh",
      "backupEnabled": true,
      "remoteConfigDir": "/homeassistant",
      "ssh": {
        "host": "10.0.2.52",
        "port": 22,
        "user": "root",
        "keyPath": "C:\\Users\\<username>\\.ssh\\id_ed25519"
      }
    }
  }
}

Commands

Install dependencies:

npm install

Compile TypeScript to Javascript:

npm run build

Run integration test suite:

npm run test-conn

Start the MCP server:

npm start

Integrating with Claude Desktop

To use HA Synapse with Claude Desktop, add it to your claude_desktop_config.json configuration (typically found at %APPDATA%\Claude\claude_desktop_config.json):

{
  "mcpServers": {
    "ha-synapse": {
      "command": "node",
      "args": ["/path/to/ha-synapse/build/index.js"],
      "env": {
        "HA_MCP_CONFIG_PATH": "/path/to/ha-synapse/ha-synapse.json"
      }
    }
  }
}

Exposed MCP Tools

• Entity Exploration:

  • get_entity_list: Returns friendly_name, entity_id, and state.

  • get_entity_details: Returns full attributes of selected entity IDs.

  • search_entities: Search by area, domain, or query matching.

• Control:

  • call_service: Execute any Home Assistant service (e.g. light.turn_on, tts.speak).

• Configuration & File Management:

  • read_ha_file: Sandbox-constrained file read.

  • write_ha_file: Safety-wrapped file writing with config validation rollback.

  • validate_ha_config: Triggers configuration check.

  • reload_ha: Reloads core, templates, automations, scripts, and themes.

  • restart_ha: Restarts the Home Assistant core.

• Orchestration & Diagnostics:

  • render_template: Evaluates Jinja2 template strings in the HA engine.

  • get_history: Fetches historical state changes.

  • get_automation_traces: Fetches run histories of automations.

  • get_automation_trace_details: Fetches execution steps of a specific trace.