# ExMCP
<div align="center">
[](https://hex.pm/packages/ex_mcp)
[](https://hexdocs.pm/ex_mcp)
[](https://github.com/azmaveth/ex_mcp/actions)
[](https://codecov.io/gh/azmaveth/ex_mcp)
[](https://github.com/azmaveth/ex_mcp/blob/master/LICENSE)
**A complete Elixir implementation of the Model Context Protocol (MCP) and Agent Client Protocol (ACP)**
[Getting Started](https://github.com/azmaveth/ex_mcp/tree/master/docs/getting-started) | [User Guide](docs/guides/USER_GUIDE.md) | [API Docs](https://hexdocs.pm/ex_mcp) | [Examples](https://github.com/azmaveth/ex_mcp/tree/master/examples) | [Changelog](CHANGELOG.md)
</div>
---
## Overview
ExMCP is a comprehensive Elixir implementation of the [Model Context Protocol](https://modelcontextprotocol.io/) and the [Agent Client Protocol](https://agentclientprotocol.com/), enabling AI models to securely interact with local and remote resources through standardized protocols. It provides both client and server implementations with multiple transport options, including native Phoenix integration via Plug compatibility, plus the ability to control coding agents like Gemini CLI, Claude Code, and Codex via ACP.
## Key Features
- **Full MCP compliance** -- protocol versions 2024-11-05, 2025-03-26, 2025-06-18, and 2025-11-25
- **100% MCP conformance** -- 226/226 client checks, 39/39 server checks (official test suite)
- **Multiple transports** -- HTTP/SSE, stdio, and BEAM-local MCP (~15μs local calls)
- **Phoenix Plug** -- native Phoenix integration with `ExMCP.HttpPlug`
- **DSL and Handler APIs** -- declarative tool/resource/prompt definitions or callback-based handlers
- **OAuth 2.1** -- automatic 401→discover→PKCE→token flow, scope step-up, CIMD, JWT client auth (`private_key_jwt`), enterprise SSO (ID-JAG), token revocation (RFC 7009), pluggable auth providers
- **OTP-native** -- supervision trees, auto-reconnection with exponential backoff, 88 telemetry events
- **Agent Client Protocol (ACP)** -- control coding agents and build native Elixir ACP agents
- **3100+ tests** -- comprehensive suite including official MCP conformance, integration, and performance
## Installation
Add `ex_mcp` to your dependencies in `mix.exs`:
```elixir
def deps do
[
{:ex_mcp, "~> 1.0.0-rc.1"}
]
end
```
## Quick Start
### Phoenix Integration
Add MCP server capabilities to your Phoenix app:
```elixir
# In your Phoenix router
defmodule MyAppWeb.Router do
use MyAppWeb, :router
scope "/api/mcp" do
forward "/", ExMCP.HttpPlug,
handler: MyApp.MCPHandler,
server_info: %{name: "my-phoenix-app", version: "1.0.0"},
sse_enabled: true,
cors_enabled: true
end
end
# Create your MCP handler
defmodule MyApp.MCPHandler do
use ExMCP.Server.Handler
@impl true
def init(_args), do: {:ok, %{}}
@impl true
def handle_initialize(_params, state) do
{:ok, %{
protocolVersion: ExMCP.protocol_version(),
serverInfo: %{name: "my-phoenix-app", version: "1.0.0"},
capabilities: %{tools: %{}, resources: %{}}
}, state}
end
@impl true
def handle_list_tools(_cursor, state) do
tools = [
%{
name: "get_user_count",
description: "Get total number of users",
inputSchema: %{type: "object", properties: %{}}
}
]
{:ok, tools, nil, state}
end
@impl true
def handle_call_tool("get_user_count", _args, state) do
count = MyApp.Accounts.count_users()
{:ok, %{content: [%{type: "text", text: "Total users: #{count}"}]}, state}
end
end
```
> **Note:** The example above uses raw `ExMCP.Server.Handler` callbacks (useful for dynamic capabilities). Most Phoenix apps will be simpler with the DSL — see the "DSL Server" section below and the [Phoenix Guide](docs/guides/PHOENIX_GUIDE.md).
### DSL Server
Define tools, resources, and prompts next to their handlers:
```elixir
defmodule MyServer do
use ExMCP.Server.Handler
use ExMCP.Server.DSL
tool "greet", "Greets a person by name" do
title "Greeting"
param :name, :string, required: true, description: "Person to greet"
run fn %{name: name}, state ->
{:ok, %{text: "Hello, #{name}!"}, state}
end
end
resource "info://about", "Server information" do
title "About"
mime_type "text/plain"
read fn %{uri: uri}, state ->
{:ok, %{uri: uri, text: "MyServer v1.0", mimeType: "text/plain"}, state}
end
end
prompt "motivate", "Create a short motivational message" do
arg :topic, required: true, description: "Topic to encourage"
render fn %{topic: topic}, state ->
{:ok,
%{
messages: [
%{role: "user", content: %{type: "text", text: "Encourage me about #{topic}"}}
]
}, state}
end
end
end
```
See the [DSL Guide](docs/DSL_GUIDE.md) and [examples](https://github.com/azmaveth/ex_mcp/tree/master/examples) for more patterns.
### Standalone Client
```elixir
# Connect to a stdio-based server
{:ok, client} = ExMCP.Client.start_link(
transport: :stdio,
command: ["node", "my-mcp-server.js"]
)
# List available tools
{:ok, tools} = ExMCP.Client.list_tools(client)
# Call a tool
{:ok, result} = ExMCP.Client.call_tool(client, "search", %{
query: "Elixir programming",
limit: 10
})
```
### BEAM-Local MCP
For trusted Elixir processes in the same VM, use the BEAM-local transport. It
carries MCP-shaped messages as Elixir terms, so local calls avoid JSON
encode/decode while still using the normal MCP client/server lifecycle.
```elixir
defmodule MyToolService do
use ExMCP.Server.Handler
use ExMCP.Server.DSL
tool "ping", "Test tool" do
run fn _args, state ->
{:ok, %{content: [%{type: "text", text: "Pong!"}]}, state}
end
end
end
{:ok, server} = MyToolService.start_link(transport: :beam)
{:ok, client} =
ExMCP.Client.start_link(
transport: :beam,
server: server
)
{:ok, tools} = ExMCP.Client.list_tools(client)
{:ok, result} = ExMCP.Client.call_tool(client, "ping", %{})
```
**Fast verification:** From the repo root (after `mix compile`), run `mix examples.getting_started` for a quick in-process demo of these patterns.
### ACP: Control and Build Coding Agents
Use the [Agent Client Protocol](https://agentclientprotocol.com/) to control coding agents programmatically or expose an Elixir process as an ACP agent:
```elixir
# Native ACP agents over stdio (Gemini CLI, Hermes, OpenCode, Qwen Code, etc.)
{:ok, client} = ExMCP.ACP.start_client(command: ["gemini", "--acp"])
# Create a session and send a prompt
{:ok, %{"sessionId" => sid}} = ExMCP.ACP.Client.new_session(client, "/my/project")
{:ok, %{"stopReason" => _}} = ExMCP.ACP.Client.prompt(client, sid, "Fix the failing tests")
# Claude Code via the SDK-compatible adapter
{:ok, client} = ExMCP.ACP.start_client(
command: ["claude"],
adapter: ExMCP.ACP.Adapters.ClaudeSDK,
adapter_opts: [model: "sonnet", cwd: "/my/project"]
)
# Pi coding agent through the ACP-native adapter
{:ok, client} = ExMCP.ACP.start_client(
command: ["pi"],
adapter: ExMCP.ACP.Adapters.Pi,
adapter_opts: [model: "anthropic/claude-sonnet-4", thinking_level: "medium"]
)
# Native Elixir ACP agent over stdio
{:ok, agent} = ExMCP.ACP.start_agent(
handler: MyApp.AgentHandler,
agent_info: %{"name" => "my-agent", "version" => "1.0.0"}
)
```
See the [ACP Guide](docs/ACP_GUIDE.md) for full details.
## Transport Performance
| Transport | Latency | Best For |
|-----------|---------|----------|
| **BEAM-local** | ~15us | Local Elixir processes in one VM |
| **stdio** | ~1-5ms | Subprocess communication |
| **HTTP/SSE** | ~5-20ms | Web applications, remote APIs |
## Documentation
### Getting Started
- **[Quick Start Guide](https://github.com/azmaveth/ex_mcp/blob/master/docs/getting-started/QUICKSTART.md)** -- Get running in 5 minutes
- **[Migration Guide](https://github.com/azmaveth/ex_mcp/blob/master/docs/getting-started/MIGRATION.md)** -- Version upgrade instructions
### Guides
- **[User Guide](docs/guides/USER_GUIDE.md)** -- Complete feature walkthrough
- **[Phoenix Integration](docs/guides/PHOENIX_GUIDE.md)** -- Detailed Phoenix/Plug integration
- **[DSL Guide](docs/DSL_GUIDE.md)** -- Declarative server definitions
- **[ACP Guide](docs/ACP_GUIDE.md)** -- Agent Client Protocol for controlling coding agents
- **[Transport Guide](docs/TRANSPORT_GUIDE.md)** -- Transport selection and optimization
- **[Configuration](docs/CONFIGURATION.md)** -- All configuration options
- **[Security](docs/SECURITY.md)** -- Authentication, TLS, and best practices
- **[Troubleshooting](docs/TROUBLESHOOTING.md)** -- Common issues and solutions
### Development & API
- **[Development Guide](docs/DEVELOPMENT.md)** -- Setup, testing, and contributing
- **[API Documentation](https://hexdocs.pm/ex_mcp)** -- Complete API reference
- **[Architecture](docs/ARCHITECTURE.md)** -- Internal design decisions
- **[Examples](https://github.com/azmaveth/ex_mcp/tree/master/examples)** -- Real-world patterns
## Contributing
Contributions welcome! See the [Development Guide](docs/DEVELOPMENT.md) for setup and testing instructions.
1. Fork the repository
2. Create a feature branch
3. Run `make quality` to ensure code quality
4. Submit a pull request
## License
MIT -- see [LICENSE](https://github.com/azmaveth/ex_mcp/blob/master/LICENSE).
## Acknowledgments
- The [Model Context Protocol](https://modelcontextprotocol.io/) and [Agent Client Protocol](https://agentclientprotocol.com/) specification creators
- The Elixir community for excellent tooling and libraries
- Contributors and early adopters providing feedback