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OpenLegion supports the Model Context Protocol (MCP) — the emerging standard for LLM tool interoperability. Any MCP-compatible tool server can be plugged into an agent via config, with tools automatically discovered and exposed to the LLM alongside built-in skills.

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Configuration

Add mcp_servers to any agent in config/agents.yaml: 
agents:
  researcher:
    role: "research"
    model: "openai/gpt-4o-mini"
    mcp_servers:
      - name: filesystem
        command: mcp-server-filesystem
        args: ["/data"]
      - name: database
        command: mcp-server-sqlite
        args: ["--db", "/data/research.db"]
Each server is launched as a subprocess inside the agent container using stdio transport. Tools are discovered automatically via the MCP protocol and appear in the LLM’s tool list alongside built-in skills.

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How It Works

  1. Agent container reads MCP_SERVERS from environment (set by the runtime)
  2. MCPClient launches each server subprocess via stdio transport
  3. MCP protocol handshake discovers available tools and their schemas
  4. Tools are registered in SkillRegistry with OpenAI function-calling format
  5. LLM tool calls route through MCPClient.call_tool() to the correct server
  6. Name conflicts with built-in skills are resolved by prefixing (mcp_{server}_{tool})

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Server Config Options

FieldTypeDescription
namestringServer identifier (used for logging and conflict prefixes)
commandstringCommand to launch the server
argslistCommand-line arguments (optional)
envdictEnvironment variables for the server process (optional)

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Example: SQLite Database Access

mcp_servers:
  - name: db
    command: mcp-server-sqlite
    args: ["--db", "/data/mydb.sqlite"]
Once configured, the agent can query the database using natural language — the MCP server translates tool calls into SQL queries.

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Example: Filesystem Access

mcp_servers:
  - name: fs
    command: mcp-server-filesystem
    args: ["/data/workspace"]
This gives the agent structured file operations beyond the built-in file tools, such as directory tree listing and file metadata.