# ExMCP
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**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
- **Multiple transports** -- HTTP/SSE, stdio, and native BEAM (~15us 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** -- Resource Server, JWT client auth (private_key_jwt), enterprise SSO (ID-JAG)
- **OTP-native** -- supervision trees, auto-reconnection with exponential backoff, telemetry
- **Agent Client Protocol (ACP)** -- control coding agents (Gemini CLI, Claude Code, Codex, etc.) over stdio
- **2600+ tests** -- comprehensive suite including TypeScript SDK interop
## Installation
Add `ex_mcp` to your dependencies in `mix.exs`:
```elixir
def deps do
[
{:ex_mcp, "~> 0.8.0"}
]
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, %{
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, [%{type: "text", text: "Total users: #{count}"}], state}
end
end
```
### DSL Server
Define tools, resources, and prompts declaratively:
```elixir
defmodule MyServer do
use ExMCP.Server
deftool "greet" do
meta do
name "Greet"
description "Greets a person by name"
end
input_schema %{
type: "object",
properties: %{name: %{type: "string", description: "Person to greet"}},
required: ["name"]
}
end
defresource "info://about" do
meta do
name "About"
description "Server information"
end
mime_type "text/plain"
end
@impl true
def handle_tool_call("greet", %{"name" => name}, state) do
{:ok, %{content: [text("Hello, #{name}!")]}, state}
end
@impl true
def handle_resource_read("info://about", _uri, state) do
{:ok, [text("MyServer v1.0")], state}
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
})
```
### Native BEAM Transport
For trusted Elixir clusters, use the native BEAM transport:
```elixir
defmodule MyToolService do
use ExMCP.Service, name: :my_tools
@impl true
def handle_mcp_request("list_tools", _params, state) do
tools = [
%{
"name" => "ping",
"description" => "Test tool",
"inputSchema" => %{"type" => "object", "properties" => %{}}
}
]
{:ok, %{"tools" => tools}, state}
end
@impl true
def handle_mcp_request("tools/call", %{"name" => "ping"}, state) do
{:ok, %{"content" => [%{"type" => "text", "text" => "Pong!"}]}, state}
end
end
# Start your service (automatically registers with ExMCP.Native)
{:ok, _} = MyToolService.start_link()
# Direct service calls (~15us latency)
{:ok, tools} = ExMCP.Native.call(:my_tools, "list_tools", %{})
```
### ACP: Control Coding Agents
Use the [Agent Client Protocol](https://agentclientprotocol.com/) to control coding agents programmatically:
```elixir
# Connect to a native ACP agent (Gemini CLI, 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")
# Use adapters for non-native agents (Claude Code, Codex)
{:ok, client} = ExMCP.ACP.start_client(
command: ["claude"],
adapter: ExMCP.ACP.Adapters.Claude
)
```
See the [ACP Guide](docs/ACP_GUIDE.md) for full details.
## Transport Performance
| Transport | Latency | Best For |
|-----------|---------|----------|
| **Native BEAM** | ~15us | Elixir cluster communication |
| **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
