The main behaviour for MCP servers.

Implement this behaviour to create a custom MCP server. If you are looking for a high-level framework to build tools and resources, see GenMCP.Suite.

Example

defmodule MyServer do
  @behaviour GenMCP

  alias GenMCP.MCP

  @impl true
  def init(_session_id, _opts) do
    {:ok, %{}}
  end

  @impl true
  def handle_request(%MCP.InitializeRequest{} = req, _channel, state) do
    # Protocol version check omitted for brevity
    result = MCP.intialize_result(
      capabilities: MCP.capabilities(tools: true),
      server_info: MCP.server_info(name: "My Server", version: "1.0.0")
    )
    {:reply, {:result, result}, state}
  end

  def handle_request(%MCP.ListToolsRequest{}, _channel, state) do
    result = MCP.list_tools_result([
      %MCP.Tool{
        name: "hello",
        description: "Say hello",
        inputSchema: %{
          type: "object",
          properties: %{
            name: %{type: "string"}
          }
        }
      }
    ])
    {:reply, {:result, result}, state}
  end

  @impl true
  def handle_notification(%MCP.InitializedNotification{}, state) do
    {:noreply, state}
  end

  def handle_notification(_notif, state) do
    {:noreply, state}
  end

  @impl true
  def handle_info(_msg, state) do
    {:noreply, state}
  end
end