yardmcp

A programmable server for exploring and querying Ruby gem documentation using YARD and the FastMCP protocol.

yardmcp exposes Ruby gem and YARD documentation as a set of programmable tools via a FastMCP server. It enables clients to:

• List installed gems with YARD docs
• Explore classes, modules, and methods
• Fetch documentation, code snippets, and source locations
• Perform fuzzy/full-text search across documentation
• Introspect inheritance, mixins, and related objects

This is useful for building documentation browsers, code assistants, or integrating Ruby/YARD docs into other systems.

• List Gems: See all installed gems with YARD documentation
• List Classes/Modules: Explore all classes/modules in a gem
• Fetch Documentation: Get docstrings, tags, parameters, return types, and more for any class/module/method
• List Children: List constants, classes, modules, and methods under a namespace
• List Methods: List all methods for a class/module
• Hierarchy: Get inheritance and inclusion info
• Ancestors: Get the full ancestor chain
• Related Objects: Find included modules, mixins, and subclasses
• Search: Fuzzy/full-text search across all documentation
• Source Location: Find the file and line number for any object
• Code Snippet: Fetch the source code for any object

You can build and install the gem locally:

gem build yardmcp.gemspec
gem install yardmcp-0.1.0.gem

This will install the yardmcp executable in your PATH.

The server is designed to be run as a long-lived process. Startup may take some time as it builds an index of all YARD documentation for installed gems. During startup, progress and logs (including Index built ...) are printed to stderr. Clients should wait for the Index built message on stderr before sending requests.

Start the server:

yardmcp

The following tools are available (use tools/list to discover):

• ListGemsTool
• ListClassesTool
• GetDocTool
• ChildrenTool
• MethodsListTool
• HierarchyTool
• SearchTool
• SourceLocationTool
• CodeSnippetTool
• AncestorsTool
• RelatedObjectsTool

See the code in lib/yardmcp.rb for argument details and return formats.

• Run tests:

  bundle exec rspec

  The test suite starts a persistent server process for all tests and waits for the server to be ready before running examples.
• Code style:

  bundle exec rubocop

• Regenerate YARD docs for a gem:

  yard gems <gemname>

• Ruby 3.2+
• Bundler
• Gems: fast-mcp, levenshtein, yard, rspec (for tests)

MIT License. See LICENSE for details.