mcpField
B
BundlerMCP

BundlerMCP

Local
rubygems.orgDeveloper Tools21Updated 69w ago
RepositoryVisit website

About BundlerMCP

BundlerMCP is an MCP server that lets AI agents query gems listed in a Ruby project's Gemfile, including their metadata and source code. It is built with fast-mcp and targets Ruby developers.

Key features

  1. 01list_project_gems tool lists bundled gems
  2. 02get_gem_details tool returns one gem's details
  3. 03Versions, descriptions and installation paths
  4. 04Locations of README and CHANGELOG files
  5. 05Optional log file and custom Gemfile path

Use cases

  1. 01AI agents looking up gem details in a Ruby project
  2. 02Finding source code and docs for a specific gem

MCP support

The server provides list_project_gems and get_gem_details tools to MCP clients for Gemfile dependency information. Clients start it by running the binstub generated in the project bin directory.

#ruby#bundler#mcp

Configuration

Local server config is the same for every client. Copy it into your client’s MCP config file.

mcp.json · Universal config
{
  "mcpServers": {
    "bundler_mcp": {
      "command": "npx",
      "args": [
        "-y",
        "@modelcontextprotocol/inspector"
      ]
    }
  }
}
Run commandnpx -y @modelcontextprotocol/inspector

Local servers need a runtime on your machine (e.g. Node.js 18+). Config file locations differ by client; see your client’s docs.

Packages
npm@modelcontextprotocol/inspector

Tools

No tool list yet

Local servers expose tools only once running on your machine, and the maintainer has not provided a tool list.

Details

From the project README

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.

CI Gem Version

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
  1. 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)

list_project_gems tool

get_gem_details

Retrieves detailed information about a specific gem, including:

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

get_gem_details tool

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

Comments

Markdown supported

New to MCP?

From what the protocol is to installing your first server, these answers cover most first questions.

An open protocol that defines how AI applications connect to external tools and data in a uniform way. Clients talk to the model; MCP servers provide tools, resources and prompt templates. They exchange standard messages, so one server can be reused by many clients.