YARD: Yay! A Ruby Documentation Tool

Homepage: http://yardoc.org
IRC: irc.freenode.net / #yard
Git: http://github.com/lsegal/yard
Author: Loren Segal
Contributors: See Contributors section below
Copyright: 2007-2011
License: MIT License
Latest Version: 0.7.3 (codename "Rhombus")
Release Date: October 15th 2011


YARD is a documentation generation tool for the Ruby programming language. It enables the user to generate consistent, usable documentation that can be exported to a number of formats very easily, and also supports extending for custom Ruby constructs such as custom class level definitions. Below is a summary of some of YARD's notable features.

Feature List

1. RDoc/SimpleMarkup Formatting Compatibility: YARD is made to be compatible with RDoc formatting. In fact, YARD does no processing on RDoc documentation strings, and leaves this up to the output generation tool to decide how to render the documentation.

2. Yardoc Meta-tag Formatting Like Python, Java, Objective-C and other languages: YARD uses a '@tag' style definition syntax for meta tags alongside regular code documentation. These tags should be able to happily sit side by side RDoc formatted documentation, but provide a much more consistent and usable way to describe important information about objects, such as what parameters they take and what types they are expected to be, what type a method should return, what exceptions it can raise, if it is deprecated, etc.. It also allows information to be better (and more consistently) organized during the output generation phase. You can find a list of tags in the Tags.md file.

YARD also supports an optional "types" declarations for certain tags. This allows the developer to document type signatures for ruby methods and parameters in a non intrusive but helpful and consistent manner. Instead of describing this data in the body of the description, a developer may formally declare the parameter or return type(s) in a single line. Consider the following method documented with YARD formatting:

 # Reverses the contents of a String or IO object. 
 # @param [String, #read] contents the contents to reverse 
 # @return [String] the contents reversed lexically 
 def reverse(contents) 
   contents = contents.read if respond_to? :read 

With the above @param tag, we learn that the contents parameter can either be a String or any object that responds to the 'read' method, which is more powerful than the textual description, which says it should be an IO object. This also informs the developer that they should expect to receive a String object returned by the method, and although this may be obvious for a 'reverse' method, it becomes very useful when the method name may not be as descriptive.

3. Custom Constructs and Extensibility of YARD: YARD is designed to be extended and customized by plugins. Take for instance the scenario where you need to document the following code:

class List
  # Sets the publisher name for the list.
  cattr_accessor :publisher

This custom declaration provides dynamically generated code that is hard for a documentation tool to properly document without help from the developer. To ease the pains of manually documenting the procedure, YARD can be extended by the developer to handle the cattr_accessor construct and automatically create an attribute on the class with the associated documentation. This makes documenting external API's, especially dynamic ones, a lot more consistent for consumption by the users.

YARD is also designed for extensibility everywhere else, allowing you to add support for new programming languages, new data structures and even where/how data is stored.

4. Raw Data Output: YARD also outputs documented objects as raw data (the dumped Namespace) which can be reloaded to do generation at a later date, or even auditing on code. This means that any developer can use the raw data to perform output generation for any custom format, such as YAML, for instance. While YARD plans to support XHTML style documentation output as well as command line (text based) and possibly XML, this may still be useful for those who would like to reap the benefits of YARD's processing in other forms, such as throwing all the documentation into a database. Another useful way of exploiting this raw data format would be to write tools that can auto generate test cases, for example, or show possible unhandled exceptions in code.

5. Local Documentation Server: YARD can serve documentation for projects or installed gems (similar to gem server) with the added benefit of dynamic searching, as well as live reloading. Using the live reload feature, you can document your code and immediately preview the results by refreshing the page; YARD will do all the work in re-generating the HTML. This makes writing documentation a much faster process.


To install YARD, use the following command:

$ gem install yard

(Add sudo if you're installing under a POSIX system as root)

Alternatively, if you've checked the source out directly, you can call rake install from the root project directory.

Important Note for Debian/Ubuntu users: there's a possible chance your Ruby install lacks RDoc, which is occasionally used by YARD to convert markup to HTML. If running which rdoc turns up empty, install RDoc by issuing:

$ sudo apt-get install rdoc


There are a couple of ways to use YARD. The first is via command-line, and the second is the Rake task.

1. yard Command-line Tool

YARD comes packaged with a executable named yard which can control the many functions of YARD, including generating documentation, graphs running the YARD server, and so on. To view a list of available YARD commands, type:

$ yard --help

Plugins can also add commands to the yard executable to provide extra functionality.

Generating Documentation

The yardoc executable is a shortcut for yard doc.

The most common command you will probably use is yard doc, or yardoc. You can type yardoc --help to see the options that YARD provides, but the easiest way to generate docs for your code is to simply type yardoc in your project root. This will assume your files are located in the lib/ directory. If they are located elsewhere, you can specify paths and globs from the commandline via:

$ yardoc 'lib/**/*.rb' 'app/**/*.rb' ...etc...

The tool will generate a .yardoc file which will store the cached database of your source code and documentation. If you want to re-generate your docs with another template you can simply use the --use-cache (or -c) option to speed up the generation process by skipping source parsing.

YARD will by default only document code in your public visibility. You can document your protected and private code by adding --protected or --private to the option switches. In addition, you can add --no-private to also ignore any object that has the @private meta-tag. This is similar to RDoc's ":nodoc:" behaviour, though the distinction is important. RDoc implies that the object with :nodoc: would not be documented, whereas YARD still recommends documenting private objects for the private API (for maintainer/developer consumption).

You can also add extra informative files (README, LICENSE) by separating the globs and the filenames with '-'.

$ yardoc 'app/**/*.rb' - README LICENSE FAQ

If no globs preceed the '-' argument, the default glob (lib/**/*.rb) is used:


Note that the README file can be specified with its own --readme switch.

You can also add a .yardopts file to your project directory which lists the switches separated by whitespace (newlines or space) to pass to yardoc whenever it is run. A full overview of the .yardopts file can be found in YARD::CLI::Yardoc.


The yardoc tool also supports a --query argument to only include objects that match a certain data or meta-data query. The query syntax is Ruby, though a few shortcuts are available. For instance, to document only objects that have an "@api" tag with the value "public", all of the following syntaxes would give the same result:

--query '@api.text == "public"'
--query 'object.has_tag?(:api) && object.tag(:api).text == "public"'
--query 'has_tag?(:api) && tag(:api).text == "public"'

Note that the "@tag" syntax returns the first tag named "tag" on the object. To return the array of all tags named "tag", use "@@tag".

Multiple --query arguments are allowed in the command line parameters. The following two lines both check for the existence of a return and param tag:

--query '@return' --query '@param'
--query '@return && @param'

For more information about the query syntax, see the YARD::Verifier class.

2. Rake Task

The second most obvious is to generate docs via a Rake task. You can do this by adding the following to your Rakefile:

YARD::Rake::YardocTask.new do |t|
  t.files   = ['lib/**/*.rb', OTHER_PATHS]   # optional
  t.options = ['--any', '--extra', '--opts'] # optional

both the files and options settings are optional. files will default to lib/**/*.rb and options will represents any options you might want to add. Again, a full list of options is available by typing yardoc --help in a shell. You can also override the options at the Rake command-line with the OPTS environment variable:

$ rake yard OPTS='--any --extra --opts'

3. yri RI Implementation

The yri binary will use the cached .yardoc database to give you quick ri-style access to your documentation. It's way faster than ri but currently does not work with the stdlib or core Ruby libraries, only the active project. Example:

$ yri YARD::Handlers::Base#register
$ yri File.relative_path

Note that class methods must not be referred to with the "::" namespace separator. Only modules, classes and constants should use "::".

You can also do lookups on any installed gems. Just make sure to build the .yardoc databases for installed gems with:

$ sudo yard gems

If you don't have sudo access, it will write these files to your ~/.yard directory. yri will also cache lookups there.

4. yard server Documentation Server

The yard server command serves documentation for a local project or all installed RubyGems. To serve documentation for a project you are working on, simply run:

$ yard server

And the project inside the current directory will be parsed (if the source has not yet been scanned by YARD) and served at http://localhost:8808.

Live Reloading

If you want to serve documentation on a project while you document it so that you can preview the results, simply pass --reload (-r) to the above command and YARD will reload any changed files on each request. This will allow you to change any documentation in the source and refresh to see the new contents.

Serving Gems

To serve documentation for all installed gems, call:

$ yard server --gems

This will also automatically build documentation for any gems that have not been previously scanned. Note that in this case there will be a slight delay between the first request of a newly parsed gem.

5. yard graph Graphviz Generator

You can use yard-graph to generate dot graphs of your code. This, of course, requires Graphviz and the dot binary. By default this will generate a graph of the classes and modules in the best UML2 notation that Graphviz can support, but without any methods listed. With the --full option, methods and attributes will be listed. There is also a --dependencies option to show mixin inclusions. You can output to stdout or a file, or pipe directly to dot. The same public, protected and private visibility rules apply to yard-graph. More options can be seen by typing yard-graph --help, but here is an example:

$ yard graph --protected --full --dependencies


  • October.15.11: 0.7.3 release

    • Improve support for parsing under Ruby 1.9.2p290 and 1.9.3 (#365, #370)
    • Add support for SWIG generated CRuby code (#369)
    • Add support for rb_define_attr calls in CRuby code (#362)
    • Handle file pointers in CRuby code (#358)
  • June.14.11: 0.7.2 release

    • Fix yard --help not showing proper output
    • YARD now expands path to .yardoc file in daemon mode for server (#328)
    • Fix @overload tag linking to wrong method (#330)
    • Fix incorrect return type when using @macro (#334)
    • YARD now requires 'thread' to support RubyGems 1.7+ (#338)
    • Fix bug in constant documentation when using %w() (#348)
    • Fix YARD style URL links when using autolinking markdown (#353)
  • May.18.11: 0.7.1 release

    • Fixes a bug in yard server not displaying class list properly.
  • May.17.11: 0.7.0 release

    • See the docs/WhatsNewdocs/WhatsNew.md document for details on added features
    • Make sure that Docstring#line_range is filled when possible (#243)
    • Set #verifier in YardocTask (#282)
    • Parse BOM in UTF-8 files (#288)
    • Fix instance attributes not showing up in method list (#302)
    • Fix rendering of %w() literals in constants (#306)
    • Ignore keyboard shortcuts when an input is active (#312)
    • And more...
  • April.14.11: 0.6.8 release

    • Fix regression in RDoc 1.x markup loading
    • Fix regression in loading of markup libraries for yard server
  • April.6.11: 0.6.7 release

    • Fix has_rdoc gem specification issue with new RubyGems plugin API (oops!)
  • April.6.11: 0.6.6 release

    • Fix error message when RDoc is not present (#270)
    • Add markup type 'none' to perform basic HTML translation (fallback when RDoc is not present)
    • Add support for RubyGems 1.7.x (#272)
    • Fix rendering of {url description} syntax when description contains newline
  • March.13.11: 0.6.5 release

    • Support ripper gem in Ruby 1.8.7
    • Upgrade jQuery to 1.5.1
    • Fix handling of alias statements with quoted symbols (#262)
    • Add CSS styles (#260)
    • Unhandled exception in YARD::Handlers::Ruby::MixinHandler indexing documentation for eventmachine (#248)
    • Splice any alias references on method re-definitions into separate methods (#247)
    • Fix "yard graph" (#245)
    • Don't process ++ typewriter text inside of HTML attributes (#244)
    • Prioritize loading of Kramdown before Maruku (#241)
    • Skip shebang encoding in docstrings (#238)
    • Fix truncation of references in @deprecated (#232)
    • Show @api private note when no other tags are present (#231)
    • Detect docstrings starting with "##" as Docstring#hash_flag (#230)
    • Remove trailing whitespace from freeform tags (#229)
    • Fix line through for deprecated methods (#225)
    • Mistake in Tags.md (#223)
    • Improve database storage by being more efficient with filesystem usage (#222)
    • Make Registry thread local (#221)
    • Support private_constant class method for 1.9.3 (#219)
    • Do not assume RDoc is installed (#214)
  • December.21.10: 0.6.4 release

    • Fix yri tool crashing with new Config class (gh-217)
    • Fix support for ::TopLevelConstants (gh-216)
    • YARD's test suite is now RSpec2 compatible (gh-215)
    • Improved documentation for YARD::Server features (gh-207)
    • Fix displaying of collaped method summary lists (gh-204)
    • Fix automatic loading of markup providers (gh-206)
    • Fix keyboard shortcuts for Chrome (gh-203)
    • Disallow extend self inside of a class (gh-202)
    • Constants now recognized in C extensions (gh-201)
  • November.21.10: 0.6.3 release

    • Fixed regression that caused yardoc --markup to silently exit
  • November.15.10: 0.6.2 release

    • Plugins no longer automatically load, use --plugin to load a plugin
    • Added YARD::Config and ~/.yard/config YAML configuration file
    • Added yard config command to view/edit YARD configuration file
    • Fixes for YARD in 1.8.6 (gh-178)
    • Various HTML template adjustments and fixes (gh-198,199,200)
    • Improved yard server -m multi-project stability (gh-193)
    • Fixed handling of yardoc --no-private with missing class definitions (gh-197)
    • Added support for constants defined in C extensions (gh-177)
    • Added support for Structs defined as "Klass = Struct.new(...)" (gh-187)
    • Improved parsing support for third-party gems (gh-174,180)
    • Improved support for JRuby 1.6.4+. YARD now passes all specs in JRuby (gh-185)
    • Improved YARD documentation (gh-172,191,196)
  • September.06.10: 0.6.1 release

    • Fixed TOC showing on top of class/method list in no-frames view
    • A message now displays when running yard server with Rack/Mongrel installed
    • Improved performance of JS inline search for large class/method lists
    • Improved link titles for relative object links
    • Removed String#camelcase and String#underscore for better Rails compat.
    • Fixed support for loading .yardoc files under Windows
    • Fixed inheritance tree arrows not displaying in certain environments
  • August.29.10: 0.6.0 release

    • Added dynamic local documentation server
    • Added @group/@endgroup declarations to organize methods into groups
    • Added yard executable to serve as main CLI tool with pluggable commands
    • Added --asset switch to yardoc to copy files/dirs to output dir
    • Added ability to register/manipulate tags via CLI (--tag, etc.)
    • Added yard diff command
    • Added statistics to yardoc output (and yard stats command)
    • Added Javascript generated Table of Contents to file pages
    • Updated various APIs
    • Removed yard-graph executable
    • See more changes in the what's new document
  • June.22.10: 0.5.8 release

    • Merge fix from 0.6 branch for --no-private visibility checking
  • June.21.10: 0.5.7 release

    • Fixed visibility flag parsing in yardoc
    • Updated Parser Architecture documentation with new SourceParser API
    • Improved Registry documentation for new load commands
    • Fix loading of .yardoc file as cache (and preserving aliases)
    • Fix "lib" directory missing when running YARD on installed gems
  • June.12.10: 0.5.6 release

    • Bug fixes for RubyGems plugin, has_rdoc=false should now work
    • New API for registering custom parsers. See WhatsNew
  • May.22.10: 0.5.5 release

    • Various bug fixes
  • March.22.10: 0.5.4 release

  • January.11.10: 0.5.3 release

  • December.16.09: 0.5.2 release

  • December.15.09: 0.5.1 release

  • December.13.09: 0.5.0 release

  • November.15.09: 0.4.0 release

    • Added new templating engine based on tadpole
    • Added YARD queries (--query CLI argument to yardoc)
    • Greatly expanded YARD documentation
    • Added plugin support
    • New @abstract and @private tags
    • Changed default rake task to rake yard
    • Read about changes in WhatsNew
  • August.13.09: release

    • Minor bug fixes.
  • August.07.09: release

    • Minor bug fixes.
  • July.26.09: release

    • Minor bug fixes.
  • July.06.09: release

    • Fix Textile hard-break issues
    • Add description for @see tag to use as link title in HTML docs.
    • Add --title CLI option to specify a title for HTML doc files.
    • Add custom.css file that can be overridden with various custom styelsheet declarations. To use this, simply add default/fulldoc/html/custom.css inside your code directory and use the -t template directory yardoc CLI option to point to that template directory (the dir holding 'default').
    • Add support in yardoc CLI to specify extra files (formerly --files) by appending "- extra files here" after regular source files. Example:

      yardoc --private lib/**/*.rb - FAQ LICENSE
  • Jun.13.09: release.

    • Add a RubyGems 1.3.2+ plugin to generate YARD documentation instead of RDoc. To take advantage of this plugin, set has_rdoc = 'yard' in your .gemspec file.
  • Jun.07.09: 0.2.3 release. See the WhatsNew file for a list of important new features.

  • Jun.16.08: 0.2.2 release. This is the largest changset since yard's conception and involves a complete overhaul of the parser and API to make it more robust and far easier to extend and use for the developer.

  • Feb.20.08: 0.2.1 release.

  • Feb.24.07: Released 0.1a experimental version for testing. The goal here is to get people testing YARD on their code because there are too many possible
    code styles to fit into a sane amount of test cases. It also demonstrates the power of YARD and what to expect from the syntax (Yardoc style meta tags).


Special thanks to all contributors for submitting patches. A full list of contributors including their patches can be found at:


YARD © 2007-2011 by Loren Segal. YARD is licensed under the MIT license except for some files which come from the RDoc/Ruby distributions. Please see the LICENSE and LEGAL documents for more information.