OpenAPI Transformer MCP server

Emcee is a tool that provides a Model Context Protocol (MCP) server for web applications with an OpenAPI specification. It allows you to connect AI assistants like Claude Desktop to external tools and data services, similar to ChatGPT plugins.

Installation Options

Using Homebrew (macOS)

For macOS users with Homebrew:

brew install mattt/tap/emcee

Using the Installer Script

Download and install a pre-built release for your platform:

# For fish shell
sh (curl -fsSL https://get.emcee.sh | psub)

# For bash or zsh
sh <(curl -fsSL https://get.emcee.sh)

Using Docker

docker run -it ghcr.io/mattt/emcee

Building From Source

Requires Go 1.24 or later:

git clone https://github.com/mattt/emcee.git
cd emcee
go build -o emcee cmd/emcee/main.go

Setting Up With Claude Desktop

1. Install Claude Desktop from claude.ai/download

2. Open Claude Desktop Settings (⌘,)

3. Select the "Developer" section in the sidebar

4. Click "Edit Config" to open the configuration file

5. Add the MCP server configuration to the file:

{
  "mcpServers": {
    "weather": {
      "command": "emcee",
      "args": ["https://api.weather.gov/openapi.json"]
    }
  }
}

6. Save the file, then quit and restart Claude

7. You should now see a 🔨 icon in the bottom right corner of your chat box, indicating available tools

Usage

Basic Command Usage

emcee [spec-path-or-url] [flags]

Available Flags

      --basic-auth string    Basic auth value (either user:pass or base64 encoded)
      --bearer-auth string   Bearer token value
  -h, --help                 help for emcee
      --raw-auth string      Raw value for Authorization header
      --retries int          Maximum number of retries for failed requests (default 3)
  -r, --rps int              Maximum requests per second (0 for no limit)
  -s, --silent               Disable all logging
      --timeout duration     HTTP request timeout (default 1m0s)
  -v, --verbose              Enable debug level logging to stderr
      --version              version for emcee

Authentication Options

For APIs requiring authentication:

Authentication Type	Example Usage	Resulting Header
Bearer Token	--bearer-auth="abc123"	Authorization: Bearer abc123
Basic Auth	--basic-auth="user:pass"	Authorization: Basic dXNlcjpwYXNz
Raw Value	--raw-auth="Custom xyz789"	Authorization: Custom xyz789

Using 1Password for Authentication

You can use 1Password secret references in the format op://vault/item/field:

{
  "mcpServers": {
    "twitter": {
      "command": "emcee",
      "args": [
        "--bearer-auth=op://shared/x/credential",
        "https://api.twitter.com/2/openapi.json"
      ]
    }
  }
}

Ensure the 1Password CLI is installed and you're signed in:

# Install op
brew install 1password-cli

# Sign in 1Password CLI
op signin

Transforming OpenAPI Specifications

You can transform specifications before passing them to emcee:

cat path/to/openapi.json | \
  jq 'if .paths then .paths |= with_entries(select(.key == "/points/{point}")) else . end' | \
  emcee

Debugging

You can use the MCP Inspector for testing and debugging:

npx @modelcontextprotocol/inspector emcee https://api.weather.gov/openapi.json
# 🔍 MCP Inspector is up and running at http://localhost:5173 🚀

Then open http://localhost:5173 in your browser.

How to install this MCP server

For Claude Code

To add this MCP server to Claude Code, run this command in your terminal:

claude mcp add-json "openapi-transformer" '{"command":"emcee","args":["https://api.weather.gov/openapi.json"]}'

See the official Claude Code MCP documentation for more details.

For Cursor

There are two ways to add an MCP server to Cursor. The most common way is to add the server globally in the ~/.cursor/mcp.json file so that it is available in all of your projects.

If you only need the server in a single project, you can add it to the project instead by creating or adding it to the .cursor/mcp.json file.

Adding an MCP server to Cursor globally

To add a global MCP server go to Cursor Settings > Tools & Integrations and click "New MCP Server".

When you click that button the ~/.cursor/mcp.json file will be opened and you can add your server like this:

{
    "mcpServers": {
        "openapi-transformer": {
            "command": "emcee",
            "args": [
                "https://api.weather.gov/openapi.json"
            ]
        }
    }
}

Adding an MCP server to a project

To add an MCP server to a project you can create a new .cursor/mcp.json file or add it to the existing one. This will look exactly the same as the global MCP server example above.

How to use the MCP server

Once the server is installed, you might need to head back to Settings > MCP and click the refresh button.

The Cursor agent will then be able to see the available tools the added MCP server has available and will call them when it needs to.

You can also explicitly ask the agent to use the tool by mentioning the tool name and describing what the function does.

For Claude Desktop

To add this MCP server to Claude Desktop:

1. Find your configuration file:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json
• Linux: ~/.config/Claude/claude_desktop_config.json

2. Add this to your configuration file:

{
    "mcpServers": {
        "openapi-transformer": {
            "command": "emcee",
            "args": [
                "https://api.weather.gov/openapi.json"
            ]
        }
    }
}

3. Restart Claude Desktop for the changes to take effect