MCP (Model Context Protocol)

The built-in MCP server was introduced in RuboCop 1.85. This feature is experimental and should not be considered stable. Changes to its behavior or interface may occur.

Model Context Protocol is an open-source standard for connecting AI applications to external systems.

This feature enables interactions through MCP clients that communicate with RuboCop via the Model Context Protocol.

Through MCP, RuboCop operations are initiated by an MCP client, with decisions made by an LLM.

The MCP server runs as a long-lived process over stdio, allowing an MCP client to request analysis and autocorrection without spawning a new RuboCop process for each request. This is based on the same principles as Server Mode and LSP.

Examples of MCP Client

For tools that support MCP clients, please refer to the following: https://modelcontextprotocol.io/clients

Below is an example for Claude Code's MCP config:

$ claude mcp add rubocop -- bundle exec rubocop --mcp

Or edit path/to/.mcp.json or something like that:

{
  "mcpServers": {
    "rubocop": {
      "type": "stdio",
      "command": "/Users/user/.rbenv/shims/bundle",
      "args": [
        "exec",
        "rubocop",
        "--mcp"
      ],
      "cwd": "/Users/user/path/to/repo"
    }
  }
}

rubocop --mcp starts the MCP server and is intended to be invoked by an MCP client, not run manually by users.