ConduitMCP

An Elixir implementation of the Model Context Protocol (MCP) specification (2025-11-25). Build MCP servers to expose tools, resources, and prompts to LLM applications like Claude Desktop, VS Code, and Cursor.

Features

• MCP Apps — Tools can return interactive UI rendered as sandboxed iframes in host clients
• Three Ways to Build — DSL macros, raw callbacks, or component modules — pick your level of control
• Full MCP Spec — Tools, resources, prompts, completion, logging, subscriptions (MCP 2025-11-25 + 2025-06-18)
• Runtime Validation — NimbleOptions-powered param validation with type coercion and custom constraints
• Stateless Architecture — Pure functions, no processes, maximum concurrency via Bandit
• Authentication — Bearer tokens, API keys, OAuth 2.1 (RFC 9728), custom verification
• Rate Limiting — HTTP-level and message-level rate limiting with Hammer
• Session Management — Pluggable session stores (ETS, Redis, PostgreSQL, Mnesia)
• Observability — Telemetry events, optional Prometheus metrics via PromEx
• Phoenix Ready — Drop-in integration with Phoenix routers
• CORS & Security — Configurable origins, preflight handling, origin validation

Installation

def deps do
  [
    {:conduit_mcp, "~> 0.9.0"}
  ]
end

Requires Elixir ~> 1.18.

Three Ways to Define Servers

ConduitMCP gives you three modes. Each is a complete, independent way to build an MCP server — pick whichever fits your project.

1. DSL Mode

Everything in one module with compile-time macros. Schemas and validation generated automatically.

defmodule MyApp.MCPServer do
  use ConduitMcp.Server

  tool "greet", "Greet someone" do
    param :name, :string, "Person's name", required: true
    param :style, :string, "Greeting style", enum: ["formal", "casual"]

    handle fn _conn, params ->
      name = params["name"]
      style = params["style"] || "casual"
      greeting = if style == "formal", do: "Good day", else: "Hey"
      text("#{greeting}, #{name}!")
    end
  end

  prompt "code_review", "Code review assistant" do
    arg :code, :string, "Code to review", required: true
    arg :language, :string, "Language", default: "elixir"

    get fn _conn, args ->
      [
        system("You are a code reviewer"),
        user("Review this #{args["language"]} code:\n#{args["code"]}")
      ]
    end
  end

  resource "user://{id}" do
    description "User profile"
    mime_type "application/json"

    read fn _conn, params, _opts ->
      user = MyApp.Users.get!(params["id"])
      json(user)
    end
  end
end

Response helpers (auto-imported): text/1, json/1, image/1, audio/2, error/1, raw/1, raw_resource/2, system/1, user/1, assistant/1 — see Responses for details and custom response patterns.

2. Manual Mode

Full control. You implement callbacks directly with raw JSON Schema maps. No compile-time magic.

defmodule MyApp.MCPServer do
  use ConduitMcp.Server, dsl: false

  @tools [
    %{
      "

... [View full README on GitHub](https://github.com/nyo16/conduit_mcp#readme)