What is Bundler Mcp

bundler_mcp is a Model Context Protocol (MCP) server that allows AI agents to query information about dependencies in a Ruby project’s Gemfile, including source code and metadata.

Use cases

Use cases for bundler_mcp include automated documentation generation, dependency analysis, and enhancing AI-driven development tools that require insights into Ruby gems.

How to use

To use bundler_mcp, install the gem by adding it to your application’s Gemfile with ‘bundle add bundler_mcp --group=development’. Then, generate the binstub using ‘bundle binstubs bundler_mcp’ and configure your client to execute the binstub.

Key features

Key features of bundler_mcp include the ability to list all bundled Ruby gems with their versions, descriptions, installation paths, and documentation locations, as well as retrieving detailed information about specific gems.

Where to use

bundler_mcp is primarily used in Ruby development environments where AI agents need to access and query information about project dependencies.

BundlerMCP

A Model Context Protocol (MCP) server enabling AI agents to query information about dependencies in a Ruby project’s Gemfile. Built with fast-mcp.

Installation

Install the gem and add to the application’s Gemfile by executing:

bundle add bundler_mcp --group=development

Usage

1. Generate the binstub:

bundle binstubs bundler_mcp

2. Configure your client to execute the binstub. Here are examples that work for Claude and Cursor:

Basic Example (mcp.json)

{
  "mcpServers": {
    "bundler-mcp": {
      "command": "/Users/mike/my_project/bin/bundler_mcp"
    }
  }
}

Example with logging and explicit Gemfile

{
  "mcpServers": {
    "bundler-mcp": {
      "command": "/Users/mike/my_project/bin/bundler_mcp",
      "env": {
        "BUNDLER_MCP_LOG_FILE": "/Users/mike/my_project/log/mcp.log",
        "BUNDLE_GEMFILE": "/Users/mike/my_project/subdir/Gemfile"
      }
    }
  }
}

Documentation

Available on RubyDoc

Available Tools

The server provides two tools for AI agents:

list_project_gems

Lists all bundled Ruby gems with their:

• Versions
• Descriptions
• Installation paths
• Top-level documentation locations (e.g. README and CHANGELOG)

get_gem_details

Retrieves detailed information about a specific gem, including:

• Version
• Description
• Installation path
• Top-level documentation locations
• Source code file locations

Environment Variables

• BUNDLE_GEMFILE: Used by Bundler to locate your Gemfile. If you use the binstub method described in the Usage section, this is usually not needed.
• BUNDLER_MCP_LOG_FILE: Path to log file. Useful for troubleshooting (defaults to no logging)

Development

After checking out the repo, run bin/setup to install dependencies and bundle exec rspec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

Testing with the MCP Inspector

You can test the server directly using the MCP inspector:

# Basic usage
npx @modelcontextprotocol/inspector ./bin/bundler_mcp

# With logging enabled
BUNDLER_MCP_LOG_FILE=/tmp/log/mcp.log npx @modelcontextprotocol/inspector ./bin/bundler_mcp

# With custom Gemfile
BUNDLE_GEMFILE=./other/Gemfile npx @modelcontextprotocol/inspector ./bin/bundler_mcp

Release Process

To install this gem onto your local machine, run bundle exec rake install. To release a new version:

1. Update the version number in version.rb
2. Run bundle exec rake release

This will:

• Create a git tag for the version
• Push git commits and the created tag
• Push the .gem file to rubygems.org

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/subelsky/bundler_mcp.

License

Open source under the terms of the MIT License.

Author

Mike Subelsky