Anubis MCP

A high-performance Model Context Protocol (MCP) implementation in Elixir.

Overview

Anubis MCP is a comprehensive Elixir SDK for the Model Context Protocol, providing complete client and server implementations with Elixir's exceptional concurrency model and fault tolerance.

Installation

def deps do
  [
    {:anubis_mcp, "~> 0.13.1"}  # x-release-please-version
  ]
end

Quick Start

Server

# Define a server with tools capabilities
defmodule MyApp.MCPServer do
  use Anubis.Server,
    name: "My Server",
    version: "1.0.0",
    capabilities: [:tools]

  @impl true
  # this callback will be called when the
  # MCP initialize lifecycle completes
  def init(_client_info, frame) do
    {:ok,frame
      |> assign(counter: 0)
      |> register_tool("echo",
        input_schema: %{
          text: {:required, :string, max: 150, description: "the text to be echoed"}
        },
        annotations: %{read_only: true},
        description: "echoes everything the user says to the LLM") }
  end

  @impl true
  def handle_tool("echo", %{text: text}, frame) do
    Logger.info("This tool was called #{frame.assigns.counter + 1}")
    {:reply, text, assign(frame, counter: frame.assigns.counter + 1)}
  end
end

# Add to your application supervisor
children = [
  Anubis.Server.Registry,
  {MyApp.MCPServer, transport: :streamable_http}
]

# Add to your Phoenix router (if using HTTP)
forward "/mcp", Anubis.Server.Transport.StreamableHTTP.Plug, server: MyApp.MCPServer

# Or if using only Plug router
forward "/mcp", to: Anubis.Server.Transport.StreamableHTTP.Plug, init_opts: [server: MyApp.MCPServer]

Now you can achieve your MCP server on http://localhost:<port>/mcp

Client

# Define a client module
defmodule MyApp.MCPClient do
  use Anubis.Client,
    name: "MyApp",
    version: "1.0.0",
    protocol_version: "2025-03-26"
end

# Add to your application supervisor
children = [
  {MyApp.MCPClient,
   transport: {:streamable_http, base_url: "http://localhost:4000"}}
]

# Use the client
{:ok, result} = MyApp.MCPClient.call_tool("echo", %{text: "this will be echoed!"})

Why Anubis?

Named after Anubis, the Egyptian god of the underworld and guide to the afterlife, this library helps navigate the boundaries between Large Language Models and external tools. Much like how Anubis guided souls through transitions, this SDK guides data through the liminal space between AI and external systems.

The name also carries personal significance - after my journey through the corporate underworld ended unexpectedly, this project was reborn from the ashes of its predecessor, ready to guide developers through their own MCP adventures. Sometimes you need a deity of transitions to help you... transition. 🏳️‍⚧️

Documentation

For detailed guides and examples, visit the official documentation.

Examples

We have build some elixir implementation examples using plug based and phoenix apps:

1. upcase-server: plug based MCP server using streamable_http
2. echo-elixir: phoenix based MCP server using sse
3. ascii-server: phoenix_live_view based MCP server using streamable_http and UI

License

LGPL-v3 License. See LICENSE for details.