mcp-proxy

mcp-proxy

• mcp-proxy
  • About
  • 1. stdio to SSE/StreamableHTTP
    • 1.1 Configuration
    • 1.2 Example usage
  • 2. SSE to stdio
    • 2.1 Configuration
    • 2.2 Example usage
  • Named Servers
  • Installation
    • Installing via PyPI
    • Installing via Github repository (latest)
    • Installing as container
    • Troubleshooting
  • Extending the container image
  • Docker Compose Setup
  • Command line arguments
    • Example config file
  • Testing

About

The mcp-proxy is a tool that lets you switch between server transports. There are two supported modes:

1. stdio to SSE/StreamableHTTP
2. SSE to stdio

1. stdio to SSE/StreamableHTTP

Run a proxy server from stdio that connects to a remote SSE server.

This mode allows clients like Claude Desktop to communicate to a remote server over SSE even though it is not supported natively.

graph LR
    A["Claude Desktop"] <--> |stdio| B["mcp-proxy"]
    B <--> |SSE| C["External MCP Server"]

    style A fill:#ffe6f9,stroke:#333,color:black,stroke-width:2px
    style B fill:#e6e6ff,stroke:#333,color:black,stroke-width:2px
    style C fill:#e6ffe6,stroke:#333,color:black,stroke-width:2px

1.1 Configuration

This mode requires providing the URL of the MCP Server's SSE endpoint as the program’s first argument. If the server uses Streamable HTTP transport, make sure to enforce it on the mcp-proxy side by passing --transport=streamablehttp.

Arguments

Environment Variables

1.2 Example usage

mcp-proxy is supposed to be started by the MCP Client, so the configuration must be done accordingly.

For Claude Desktop, the configuration entry can look like this:

{
  "mcpServers": {
    "mcp-proxy": {
      "command": "mcp-proxy",
      "args": [
        "http://example.io/sse"
      ],
      "env": {
        "API_ACCESS_TOKEN": "access-token"
      }
    }
  }
}

2. SSE to stdio

Run a proxy server exposing a SSE server that connects to a local stdio server.

This allows remote connections to the local stdio server. The mcp-proxy opens a port to listen for SSE requests, spawns a local stdio server that handles MCP requests.

graph LR
    A["LLM Client"] <-->|SSE| B["mcp-proxy"]
    B <-->|stdio| C["Local MCP Server"]

    style A fill:#ffe6f9,stroke:#333,color:black,stroke-width:2px
    style B fill:#e6e6ff,stroke:#333,color:black,stroke-width:2px
    style C fill:#e6ffe6,stroke:#333,color:black,stroke-width:2px

2.1 Configuration

This mode requires the --sse-port argument to be set. The --sse-host argument can be set to specify the host IP address that the SSE server will listen on. Additional environment variables can be passed to the local stdio server using the --env argument. The command line arguments for the local stdio server must be passed after the -- separator.

Arguments

2.2 Example usage

To start the mcp-proxy server that listens on port 8080 and connects to the local MCP server:

…

Named Servers

• NAME is used in the URL path /servers/NAME/.
• COMMAND_STRING is the command to start the server (e.g., 'uvx mcp-server-fetch').
  • Can be used multiple times.
  • This argument is ignored if --named-server-config is used.
• FILE_PATH - If provided, this is the exclusive source for named servers, and --named-server CLI arguments are ignored.

If a default server is specified (the command_or_url argument without --named-server or --named-server-config), it will be accessible at the root paths (e.g., http://127.0.0.1:8080/sse).

Named servers (whether defined by --named-server or --named-server-config) will be accessible under /servers/<server-name>/ (e.g., http://127.0.0.1:8080/servers/fetch1/sse). The /status endpoint provides global status.

JSON Configuration File Format for --named-server-config:

The JSON file should follow this structure:

{
  "mcpServers": {
    "fetch": {
      "disabled": false,
      "timeout": 60,
      "command": "uvx",
      "args": [
        "mcp-server-fetch"
      ],
      "transportType": "stdio"
    },
    "github": {
      "timeout": 60,
      "command": "npx",
      "args": [
        "-y",
        "@modelcontextprotocol/server-github"
      ],
      "env": {
        "GITHUB_PERSONAL_ACCESS_TOKEN": "<YOUR_TOKEN>"
      },
      "transportType": "stdio"
    }
  }
}

• mcpServers: A dictionary where each key is the server name (used in the URL path, e.g., /servers/fetch/) and the value is an object defining the server.
• command: (Required) The command to execute for the stdio server.
• args: (Optional) A list of arguments for the command. Defaults to an empty list.
• enabled: (Optional) If false, this server definition will be skipped. Defaults to true.
• timeout and transportType: These fields are present in standard MCP client configurations but are currently ignored by mcp-proxy when loading named servers. The transport type is implicitly "stdio".

Installation

Installing via PyPI

The stable version of the package is available on the PyPI repository. You can install it using the following command:

# Option 1: With uv (recommended)
uv tool install mcp-proxy

# Option 2: With pipx (alternative)
pipx install mcp-proxy

Once installed, you can run the server using the mcp-proxy command. See configuration options for each mode above.

Installing via Github repository (latest)

The latest version of the package can be installed from the git repository using the following command:

uv tool install git+https://github.com/sparfenyuk/mcp-proxy

[!NOTE] If you have already installed the server, you can update it using uv tool upgrade --reinstall command.

[!NOTE] If you want to delete the server, use the uv tool uninstall mcp-proxy command.

Installing as container

Starting from version 0.3.2, it's possible to pull and run the corresponding container image. Release images are published to GHCR and Docker Hub as multi-platform manifests for linux/amd64 and linux/arm64; Docker selects the matching image for the host architecture automatically.

docker run --rm -t ghcr.io/sparfenyuk/mcp-proxy:v0.12.0 --help
docker run --rm -t sparfenyuk/mcp-proxy:v0.12.0 --help

Troubleshooting

• Problem: Claude Desktop can't start the server: ENOENT code in the logs

  Solution: Try