MCPhoenix

MCPhoenix

MCP server built on Phoenix Framework (Elixir). Exposes Server-Sent Events and JSON-RPC endpoints for MCP clients, with support for managing multiple child MCP servers through JSON configuration.

Note: the module and directory names use the spelling "MCPheonix" (without the 'o') throughout the codebase.

What It Does

Runs a Phoenix web server on port 4001 that:

1. Accepts MCP JSON-RPC requests at POST /mcp/rpc
2. Streams events to clients via SSE at GET /mcp/stream
3. Manages child MCP servers (Flux image generation, Dart task management, etc.) as supervised processes
4. Routes tool calls to the appropriate child server over stdio

Child servers are defined in priv/config/mcp_servers.json and started automatically at boot.

Status

| Area | State | |------|-------| | Transport | HTTP (SSE + JSON-RPC) | | Framework | Phoenix 1.7, Elixir >= 1.14, Erlang >= 25 | | Child MCP servers | Flux (image generation), Dart (task management) | | OTP supervision | Yes — child servers are supervised processes | | Cloudflare integration | Durable Objects client (experimental, uses custom hex package) | | Event system | Broadway + GenStage for processing pipelines | | Tests | ExUnit, 2 test files (Cloudflare DO client, mock websocket) | | License | MIT |

Architecture

lib/
  mcpheonix/
    application.ex         — OTP application, supervision tree
    mcp/
      server.ex            — Core MCP server logic
      server_manager.ex    — Manages child MCP server processes
      server_process.ex    — GenServer wrapping a child stdio process
      supervisor.ex        — Supervisor for MCP server processes
      config.ex            — Reads mcp_servers.json
      connection.ex        — Client connection state
      json_rpc_protocol.ex — JSON-RPC 2.0 parsing
      jsonrpc_client.ex    — Client for calling child servers
      flux_server.ex       — Flux-specific server config
      features/
        resources.ex       — Resource listing
        tools.ex           — Tool listing and dispatch
    events/
      broker.ex            — Pub/sub event broker
    cloud/
      durable_objects/
        client.ex          — Cloudflare Durable Objects HTTP client
    resources/
      message.ex, registry.ex, user.ex — Domain resources (Ash framework)
  mcpheonix_web/
    endpoint.ex            — Phoenix endpoint
    router.ex              — Routes: /mcp/stream (SSE), /mcp/rpc (JSON-RPC)
    controllers/
      mcp_controller.ex    — SSE stream and RPC handler
      page_controller.ex   — Default page
    plugs/
      mcp_rpc_plug.ex      — Parses JSON-RPC body
      raw_body_*.ex        — Raw body reading for RPC

Adding MCP Servers

Edit priv/config/mcp_servers.json:

{
  "mcpServers": {
    "your_server": {
      "command": "/path/to/executable",
      "args": ["arg1"],
      "env": { "API_KEY": "value" },
      "tools": {
        "tool_name": {
          "description": "What it does",
          "parameters": [
            { "name": "param1", "type": "string", "description": "..." }
          ]
        }
      }
    }
  }
}

Servers are started as child processes under OTP supervision and restarted on failure.

Setup

git clone https://github.com/jmanhype/MCPhoenix.git
cd MCPhoenix       # note: the repo name uses correct spelling
mix deps.get
mix phx.server     # starts on port 4001

Requirements

| Dependency | Version | |-----------|---------| | Elixir | >= 1.14 | | Erlang/OTP | >= 25 | | Phoenix | ~> 1.7.0 | | Node.js | >= 18 (for child MCP servers) | | Python | >= 3.9 (for Flux/Dart integration) |

Optional Integrations

| Integration | What's Needed | |------------|---------------| | Flux image generation | Python 3.9+, Flux CLI, BFL_API_KEY | | Dart task management | Node.js 18+, DART_TOKEN | | Cloudflare Durable Objects | Worker deployment, CLOUDFLARE_WORKER_URL, CLOUDFLARE_ACCOUNT_ID, CLOUDFLARE_API_TOKEN |

MCP Endpoints

| Endpoint | Method | Purpose | |----------|--------|---------| | /mcp/stream | GET | SSE stream; returns x-mcp-client-id header | | /mcp/rpc | POST | JSON-RPC 2.0; pass x-mcp-client-id header |

Key Dependencies

| Package | Version | Purpose | |---------|---------|---------| | phoenix | ~> 1.7.0 | Web framework | | phoenix_live_view | ~> 0.19.0 | LiveView (included but not primary interface) | | ash | ~> 2.9 | Resource framework | | broadway | ~> 1.0 | Event processing | | gen_stage | ~> 1.2 | Event streams | | finch | ~> 0.16 | HTTP client | | mint_web_socket | ~> 1.0 | WebSocket support | | jason | ~> 1.4 | JSON encoding |

Limitations

• The Cloudflare Durable Objects integration depends on a custom GitHub hex package (cloudflare_durable_ex) that may not be publicly available
• No authentication on the MCP endpoints
• SSE connections are not persisted across server restarts
• The Ash framework resources (User, Message, Registry) appear scaffolded but not fully integrated
• LiveView and LiveDashboard are included but not used for the MCP interface
• Log files (dev.log, phoenix_server.log) and temporary files are committed to the repo

License

MIT

Source & license

This open-source MCP server is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: jmanhype
• Source: jmanhype/MCPhoenix
• License: MIT

Install and usage instructions live in the source repository linked above.