Tools & Extensions

How extensions provide tool-level capabilities to Tars through the Model Context Protocol.

Overview

Extensions are MCP (Model Context Protocol) servers that expose tools to Tars. They run as separate processes and communicate via stdio, allowing Tars to interact with external systems, manage files, and extend its own intelligence.

How Extensions Work

1. Engine Initialization: During startup, GeminiEngine scans ~/.tars/.gemini/extensions/ for gemini-extension.json files.
2. Manifest Parsing: The engine converts the manifest into an internal MCPServerConfig, resolving ${extensionPath} tokens to absolute paths.
3. Discovery: High-level tools from all enabled extensions are merged into the Gemini Core’s tool definition list.
4. Execution: When the AI invokes a tool, the Core library manages the stdio connection to the extension’s binary (e.g., node server.js).

Extension Structure

Each extension is an npm package with a manifest:

// gemini-extension.json
{
    "name": "tars-tasks",
    "version": "1.0.0",
    "mcpServers": {
        "main": {
            "command": "node",
            "args": ["${extensionPath}/dist/server.js"],
            "env": { "TARS_HOME": "~/.tars" }
        }
    }
}

Deployment & Sync

Tars manages extensions through its internal bootstrap process:

• Built-in Extensions: Source code from the repository’s extensions/ directory is copied to ~/.tars/.gemini/extensions/ on startup.
• Runtime Extensions: Created via the extension-builder skill directly in the target directory.

Extension Enablement

Extensions must be authorized in ~/.tars/.gemini/extensions/extension-enablement.json. Tars uses this file to manage security overrides:

{
    "tars-tasks": { "overrides": ["*"] },
    "tars-memory": { "overrides": ["*"] }
}

Creating Custom Extensions

Tars is capable of self-modifying its own toolset via the extension-builder skill. The process involves:

1. Generating a plain JavaScript MCP server using @modelcontextprotocol/sdk.
2. Creating the gemini-extension.json manifest with relative path tokens.
3. Registering the new extension in the enablement configuration.

Core Extensions

Detailed documentation for each can be found in the Extensions section.