EMCP

Add the emcp package to your project's dependency list. Check hex.pm/packages/emcp for the current version number.

# In mix.exs deps:
{:emcp, "~> 0.1"}

Download and compile the EMCP library and its transitive dependencies.

mix deps.get

Add the ETS session store initialization to your application's start/2 function in lib/my_app/application.ex so sessions persist across requests.

def start(_type, _args) do
  EMCP.SessionStore.ETS.init()
  # ... rest of your supervision tree
end

Create a module that uses EMCP.Server and declares which tools, prompts, and resources it exposes. Each tool, prompt, and resource is its own module implementing the relevant behaviour.

defmodule MyApp.MCPServer do
  use EMCP.Server,
    name: "my-app",
    version: "1.0.0",
    tools: [MyApp.Tools.Echo],
    prompts: [MyApp.Prompts.CodeReview],
    resources: [MyApp.Resources.Readme]
end

Add the StreamableHTTP transport outside any pipeline scope so it handles MCP JSON-RPC requests at the /mcp path.

scope "/mcp" do
  forward "/", EMCP.Transport.StreamableHTTP, server: MyApp.MCPServer
end

For Claude Code, add the server to .claude/settings.json using the mix run command. For Claude Desktop with a running Phoenix server, use an HTTP transport URL pointing at the /mcp endpoint.

{
  "mcpServers": {
    "my-app": {
      "command": "mix",
      "args": ["run", "--no-halt"],
      "cwd": "/path/to/your/elixir/project"
    }
  }
}