RDOC - Ruby Documentation System

This package contains RDoc and RDoc::Markup. RDoc is an application that produces documentation for one or more Ruby source files. We work similarly to JavaDoc, parsing the source, and extracting the definition for classes, modules, and methods (along with includes and requires). We associate with these optional documentation contained in the immediately preceding comment block, and then render the result using a pluggable output formatter. RDoc::Markup is a library that converts plain text into various output formats. The markup library is used to interpret the comment blocks that RDoc uses to document methods, classes, and so on.


  • If you want to use RDoc to create documentation for your Ruby source files, read on.

  • If you want to include extensions written in C, see RDoc::C_Parser

  • For information on the various markups available in comment blocks, see RDoc::Markup.

  • If you want to drive RDoc programmatically, see RDoc::RDoc.

  • If you want to use the library to format text blocks into HTML, have a look at RDoc::Markup.

  • If you want to try writing your own HTML output template, see RDoc::Generator::HTML


Once installed, you can create documentation using the ‘rdoc’ command (the command is ‘rdoc.bat’ under Windows)

% rdoc [options] [names...]

Type “rdoc –help” for an up-to-date option summary.

A typical use might be to generate documentation for a package of Ruby source (such as rdoc itself).

% rdoc

This command generates documentation for all the Ruby and C source files in and below the current directory. These will be stored in a documentation tree starting in the subdirectory ‘doc’.

You can make this slightly more useful for your readers by having the index page contain the documentation for the primary file. In our case, we could type

% rdoc --main rdoc.rb

You’ll find information on the various formatting tricks you can use in comment blocks in the documentation this generates.

RDoc uses file extensions to determine how to process each file. File names ending .rb and .rbw are assumed to be Ruby source. Files ending .c are parsed as C files. All other files are assumed to contain just Markup-style markup (with or without leading '#' comment markers). If directory names are passed to RDoc, they are scanned recursively for C and Ruby source files only.


For information on how to make lists, hyperlinks, & etc. with RDoc, see RDoc::Markup.

Comment blocks can be written fairly naturally, either using ‘#’ on successive lines of the comment, or by including the comment in an =begin/=end block. If you use the latter form, the =begin line must be flagged with an RDoc tag:

=begin rdoc
Documentation to be processed by RDoc.


RDoc stops processing comments if it finds a comment line containing '#--'. This can be used to separate external from internal comments, or to stop a comment being associated with a method, class, or module. Commenting can be turned back on with a line that starts '+#+++'.

# Extract the age and calculate the date-of-birth.
# FIXME: fails if the birthday falls on February 29th
# The DOB is returned as a Time object.

def get_dob(person)
  # ...

Names of classes, source files, and any method names containing an underscore or preceded by a hash character are automatically hyperlinked from comment text to their description.

Method parameter lists are extracted and displayed with the method description. If a method calls yield, then the parameters passed to yield will also be displayed:

def fred
  yield line, address

This will get documented as:

fred() { |line, address| ... }

You can override this using a comment containing ‘:yields: …’ immediately after the method definition

def fred # :yields: index, position
  # ...

  yield line, address

which will get documented as

fred() { |index, position| ... }

:yields: is an example of a documentation directive. These appear immediately after the start of the document element they are modifying.


:nodoc: / :nodoc: all

Don’t include this element in the documentation. For classes and modules, the methods, aliases, constants, and attributes directly within the affected class or module will also be omitted. By default, though, modules and classes within that class of module will be documented. This is turned off by adding the all modifier.

module MyModule # :nodoc:
  class Input

module OtherModule # :nodoc: all
  class Output

In the above code, only class +MyModule::Input+ will be documented.


Force a method or attribute to be documented even if it wouldn’t otherwise be. Useful if, for example, you want to include documentation of a particular private method.


Only applicable to the initialize instance method. Normally RDoc assumes that the documentation and parameters for initialize are actually for the ::new method, and so fakes out a ::new for the class. The :notnew: modifier stops this. Remember that initialize is protected, so you won’t see the documentation unless you use the -a command line option.

Comment blocks can contain other directives:

+:section: title+

Starts a new section in the output. The title following :section: is used as the section heading, and the remainder of the comment containing the section is used as introductory text. Subsequent methods, aliases, attributes, and classes will be documented in this section. A :section: comment block may have one or more lines before the :section: directive. These will be removed, and any identical lines at the end of the block are also removed. This allows you to add visual cues such as:

# ----------------------------------------
# :section: My Section
# This is the section that I wrote.
# See it glisten in the noon-day sun.
# ----------------------------------------

Lines up to the next blank line in the comment are treated as the method’s calling sequence, overriding the default parsing of method parameters and yield arguments.

:include: filename

Include the contents of the named file at this point. The file will be searched for in the directories listed by the --include option, or in the current directory by default. The contents of the file will be shifted to have the same indentation as the ‘:’ at the start of the :include: directive.

:title: text

Sets the title for the document. Equivalent to the –title command line parameter. (The command line parameter overrides any :title: directive in the source).


Document nothing further at the current level.

:main: name

Equivalent to the –main command line parameter.

:stopdoc: / :startdoc:

Stop and start adding new documentation elements to the current container. For example, if a class has a number of constants that you don’t want to document, put a :stopdoc: before the first, and a :startdoc: after the last. If you don’t specify a :startdoc: by the end of the container, disables documentation for the entire class or module.

Other stuff


Dave Thomas <dave@pragmaticprogrammer.com>


  • The Ruby parser in rdoc/parse.rb is based heavily on the outstanding work of Keiju ISHITSUKA of Nippon Rational Inc, who produced the Ruby parser for irb and the rtags package.

  • Code to diagram classes and modules was written by Sergey A Yanovitsky (Jah) of Enticla.

  • Charset patch from MoonWolf.

  • Rich Kilmer wrote the kilmer.rb output template.

  • Dan Brickley led the design of the RDF format.


RDoc is Copyright (c) 2001-2003 Dave Thomas, The Pragmatic Programmers. It is free software, and may be redistributed under the terms specified in the README file of the Ruby distribution.


This software is provided “as is” and without any express or implied warranties, including, without limitation, the implied warranties of merchantibility and fitness for a particular purpose.