Markdown is a plain text formatting syntax^[5] designed so that it can optionally be converted to HTML using a tool by the same name. Markdown is popularly used as format for readme files, or for writing messages in online discussion forums, or in text editors for the quick creation of rich text documents.

History

The Markdown language was created in 2004 by John Gruber with substantial contributions from Aaron Swartz,^[6] with the goal of allowing people “to write using an easy-to-read, easy-to-write plain text format, and optionally convert it to structurally valid XHTML (or HTML)”.^[3]

Taking cues from existing conventions for marking up plain text in email, the language was designed to be readable as-is, without looking like it's been marked up with tags or formatting instructions,^[7] unlike text which has been formatted with a Markup language, such as HTML, which has obvious tags and formatting instructions. Markdown is a formatting syntax for text that can be read by humans and can be easily converted to HTML.

Gruber wrote a Perl script, Markdown.pl, which converts marked-up text input to valid, well-formed XHTML or HTML and replaces left-pointing angle brackets ('<') and ampersands with their corresponding character entity references. It can be used as a standalone script, as a plugin for Blosxom or Movable Type, or as a text filter for BBEdit.^[3]

Markdown has since been re-implemented by others as a Perl module available on CPAN (Text::Markdown), and in a variety of other programming languages. It is distributed under a BSD-style license^[4] and is included with, or available as a plugin for, several content-management systems.^[8][9]

Sites such as GitHub, reddit, Diaspora, Stack Overflow, OpenStreetMap, and SourceForge use variants of Markdown to facilitate discussion between users.^{[10][11][12][13]}

Standardization

There is no clearly defined Markdown standard, apart from the original writeup and implementation by John Gruber, which is considered to be abandonware,^[14][15] leading to fragmentation as different vendors write their own variants of the language to correct flaws or add missing features. In late 2012, a standardization effort was started, spurred in part by a blog post of Jeff Atwood.^[16] A community website now aims to "document various tools and resources available to document authors and developers, as well as implementors of the various markdown implementations".^[17] A tool (named Babelmark2^[18]) is also available to "[compare] the output of various implementations" to "promote discussion of how and whether certain vague aspects of the markdown spec should be clarified".^[19]

Example

The following shows on the left, text using Markdown syntax, in the center, the corresponding HTML produced by a Markdown processor, and on the right, the text viewed in a browser.

Heading 
=======

Sub-heading
-----------

Paragraphs are separated
by a blank line.

Text attributes *italic*,
**bold**, `monospace`.

A [link](http://example.com).

Shopping list:

  * apples
  * oranges
  * pears

Numbered list:

  1. apples
  2. oranges
  3. pears

The rain---not the reign---in
Spain.

<h1>Heading</h1>
 
<h2>Sub-heading</h2>
 
<p>Paragraphs are separated
by a blank line.</p>
 
<p>Text attributes <em>italic</em>,
<strong>bold</strong>,
<code>monospace</code>.</p>
 
<p>A <a href="http://example.com">link</a>.</p>
 
<p>Shopping list:</p>
 
<ul>
<li>apples</li>
<li>oranges</li>
<li>pears</li>
</ul>
 
<p>Numbered list:</p>
 
<ol>
<li>apples</li>
<li>oranges</li>
<li>pears</li>
</ol>
 
<p>The rain&mdash;not the
reign&mdash;in Spain.</p>

Editors

While Markdown is a minimal markup language and is easily read and edited with a normal text editor, there are specially-designed editors which preview the files with styles. There are a variety of such editors available for all major platforms, and there are syntax highlighting plugins for markdown built into emacs, gedit, and vim.

Implementations

Implementations of Markdown are available for many different frameworks, platforms and languages.

• The sourcecode documentation generator Doxygen supports Markdown with extra features.^[20]
• RStudio, an IDE for R provides a C++ wrapper function for the markdown implementation sundown.^[21]
• IntelliJ IDEA, an IDE for Java, provides a Markdown plugin^[22][23]
• MultiMarkdown A format and program with more syntax features and export options than traditional Markdown
• "GitHub Flavored Markdown" (GFM) has several implementations.^{[24][25][26][27]} GFM adds syntax highlighting, task lists and tables to standard Markdown.^[10]

There are many more open-source software implementations of Markdown available online.

See also

• Markdown enhancements:
  • Markdown extensions
  • Markdown Extra
• Similar lightweight markup languages:
  • AsciiDoc, supports many document types
  • Org-mode
  • reStructuredText, used for Python documentation
  • POD, used for Perl documentation
  • Setext, from 1992
  • Textile
  • txt2tags
• Comparison of document markup languages
• Comparison of documentation generators

References

External links

• Official Markdown project at Daring Fireball
• Markdown community page