Showdown is a JavaScript Bidirectional Markdown HTML converter, based on the original works by John Gruber.
Showdown can be used client side (in the browser) or server side (with Node.js).
Showdown can convert Markdown to HTML and HTML to Markdown.
Live DEMO
http://demo.showdownjs.eu/
As you know, ShowdownJS is a free library and it will remain free forever. However, maintaining and improving the library costs time and money.
If you like our work and find our library useful, please donate through PayPal! Your contribution will be greatly appreciated and help me continue to develop this awesome library.
License
ShowdownJS (from v2.0 onwards) is released under the MIT license.
Previous versions are released under BSD.
Who uses Showdown (or a fork)
Installation
Download tarball
You can download the latest release tarball directly from releases.
Bower
bower install showdown
npm (server-side)
npm install showdown
NuGet package
PM> Install-Package showdownjs
The NuGet Packages can be found here.
CDN
You can also use one of several CDNs available:
jsDelivr
https://cdn.jsdelivr.net/npm/showdown@<version tag>/dist/showdown.min.js
cdnjs
https://cdnjs.cloudflare.com/ajax/libs/showdown/<version tag>/showdown.min.js
unpkg
https://unpkg.com/showdown/dist/showdown.min.js
Note: replace <version tag> with an actual full length version you're interested in e.g. 1.9.0
Browser Compatibility
Showdown has been tested successfully with:
- Firefox 1.5 and 2.0
- Chrome 12.0
- Internet Explorer 6 and 7
- Safari 2.0.4
- Opera 8.54 and 9.10
- Netscape 8.1.2
- Konqueror 3.5.4
In theory, Showdown will work in any browser that supports ECMA 262 3rd Edition (JavaScript 1.5).
The converter itself might even work in things that aren't web browsers, like Acrobat. No promises.
Node compatibility
Showdown is intended to work on any supported Node.js version (see the Node.js releases schedule. The code may work with previous versions of Node.js, but no accomidations are made to ensure it does.
Legacy version
If you're looking for showdown v<1.0.0, you can find it in the legacy branch.
Changelog
You can check the full changelog
Extended documentation
Check our wiki pages for examples and a more in-depth documentation.
Quick Example
Node
var showdown = require('showdown'),
converter = new showdown.Converter(),
text = '# hello, markdown!',
html = converter.makeHtml(text);
Browser
var converter = new showdown.Converter(),
text = '# hello, markdown!',
html = converter.makeHtml(text);
Output
Both examples should output...
<h1 id="hello-markdown">hello, markdown!</h1>
Options
You can change some of showdown's default behavior through options.
Setting options
Options can be set:
Globally
Setting a "global" option affects all instances of showdown
showdown.setOption('optionKey', 'value');
Locally
Setting a "local" option only affects the specified Converter object.
Local options can be set:
through the constructor
var converter = new showdown.Converter({optionKey: 'value'});
through the setOption() method
var converter = new showdown.Converter();
converter.setOption('optionKey', 'value');
Getting an option
Showdown provides 2 methods (both local and global) to retrieve previous set options.
getOption()
// Global
var myOption = showdown.getOption('optionKey');
//Local
var myOption = converter.getOption('optionKey');
getOptions()
// Global
var showdownGlobalOptions = showdown.getOptions();
//Local
var thisConverterSpecificOptions = converter.getOptions();
Retrieve the default options
You can get showdown's default options with:
var defaultOptions = showdown.getDefaultOptions();
Valid Options
omitExtraWLInCodeBlocks: (boolean) [default false] Omit the trailing newline in a code block. Ex:
This:
<code><pre>var foo = 'bar';
</pre></code>
Becomes this:
<code><pre>var foo = 'bar';</pre></code>
headerIds: (false | object) [default {}] Controls the id attribute generated on headings. Accepts either
false (no ids at all) or an object {prefix, raw}:
{} (the default) — github-compatible ids (spaces become dashes and most non-alphanumeric chars are stripped), no prefix.prefix (string) — prepended to every generated id, e.g. {prefix: 'section-'}.raw: true — minimal sanitization: replace only spaces, ', ", > and < with dashes (-), including in any prefix,
instead of the default github-compatible style. WARNING: This might result in malformed ids.- The
prefix and raw settings can be combined, e.g. {prefix: '/p/', raw: true}.
NOTE: this option replaces the removed noHeaderId, prefixHeaderId and rawHeaderId options.
noHeaderId: true → headerIds: false; prefixHeaderId: 'foo' → headerIds: {prefix: 'foo'}; rawHeaderId: true → headerIds: {raw: true}.
headerLevelStart: (integer) [default 1] Set the header starting level. For instance, setting this to 3 means that
# foo
will be parsed as
<h3>foo</h3>
parseImgDimensions: (boolean) [default false] Enable support for setting image dimensions from within markdown syntax.
Examples:
 simple, assumes units are in px
 sets the height to "auto"
 Image with width of 80% and height of 5em
simplifiedAutoLink: (boolean) [default false] Turning this option on will enable automatic linking to urls.
This means that:
some text www.google.com
will be parsed as
<p>some text <a href="www.google.com">www.google.com</a>
httpsAutoLinks: (boolean) [default false] Use https:// instead of http:// for the protocol added to
autolinked www. urls. Only applies if simplifiedAutoLink option is set to true. (since v3.0.0)
literalMidWordUnderscores: (boolean) [default false] Turning this on will stop showdown from interpreting
underscores in the middle of words as <em> and <strong> and instead treat them as literal underscores.
Example:
some text with__underscores__in middle
will be parsed as
<p>some text with__underscores__in middle</p>
strikethrough: (boolean) [default true] Enable support for strikethrough syntax.
~~strikethrough~~ as <del>strikethrough</del>
tables: (boolean) [default false] Enable support for tables syntax. Example:
| h1 | h2 | h3 |
|:------|:-------:|--------:|
| 100 | [a][1] | ![b][2] |
| *foo* | **bar** | ~~baz~~ |
See the wiki for more info
tablesHeaderId: (boolean) [default false] If enabled adds an id property to table headers tags.
ghCodeBlocks: (boolean) [default true] Enable support for GFM code block style.
tasklists: (boolean) [default false] Enable support for GFM tasklists. Example:
- [x] This task is done
- [ ] This is still pending
smartIndentationFix: (boolean) [default false] Tries to smartly fix indentation problems related to es6 template
strings in the midst of indented code.
disableForced4SpacesIndentedSublists: (boolean) [default false] Disables the requirement of indenting sublists
by 4 spaces for them to be nested, effectively reverting to the old behavior where 2 or 3 spaces were enough.
(since v1.5.0)
simpleLineBreaks: (boolean) [default false] Parses line breaks as <br>, without
needing 2 spaces at the end of the line (since v1.5.1)
a line
wrapped in two
turns into:
<p>a line<br>
wrapped in two</p>
ghMentions: (boolean) [default false] Enables github @mentions, which link to the username mentioned (since v1.6.0)
ghMentionsLink: (string) [default https://github.com/{u}] Changes the link generated by @mentions.
Showdown will replace {u} with the username. Only applies if ghMentions option is enabled.
Example: @tivie with ghMentionsOption set to //mysite.com/{u}/profile will result in <a href="//mysite.com/tivie/profile">@tivie</a>
encodeEmails: (boolean) [default true] Enable e-mail addresses encoding through the use of Character Entities, transforming ASCII e-mail addresses into its equivalent decimal entities. (since v1.6.1)
NOTE: Prior to version 1.6.1, emails would always be obfuscated through dec and hex encoding.
backslashEscapesHTMLTags: (boolean) [default false] Support for HTML Tag escaping. ex: \<div>foo\</div> (since v1.7.2)
emoji: (boolean) [default false] Enable emoji support. Ex: this is a :smile: emoji
For more info on available emojis, see https://github.com/showdownjs/showdown/wiki/Emojis (since v.1.8.0)
underline: (boolean) [default false] EXPERIMENTAL FEATURE Enable support for underline.
Syntax is double or triple underscores ex: __underlined word__. With this option enabled, underscores are no longer parses into <em> and <strong>.
ellipsis: (boolean) [default true] Replaces three dots with the ellipsis unicode character.
completeHTMLDocument: (boolean) [default false] Outputs a complete html document,
including <html>, <head> and <body> tags' instead of an HTML fragment. (since v.1.8.5)
metadata: (boolean) [default false] Enable support for document metadata (defined at the top of the document
between ««« and »»» or between --- and ---). (since v.1.8.5)
var conv = new showdown.Converter({metadata: true});
var html = conv.makeHtml(someMd);
var metadata = conv.getMetadata(); // returns an object with the document metadata
splitAdjacentBlockquotes: (boolean) [default false] Split adjacent blockquote blocks.(since v.1.8.6)
moreStyling: (boolean) [default false] Adds some useful classes for css styling. (since v3.0.0)
- Tasklists: Adds the class
task-list-item-complete to completed tasks items in GFM tasklists.
relativePathBaseUrl: (string) [default ''] Prepends a base URL to relative paths (in links and images).
Absolute paths (starting with a protocol, //, or #) are left untouched. (since v3.0.0)
Security options
By default Showdown follows the trusted-input model and does not sanitize (see XSS vulnerability). The options below add opt-in, defense-in-depth hardening for when the Markdown source is untrusted. They are not a replacement for a dedicated HTML sanitizer.
safeMode: (boolean) [default false] Defense-in-depth hardening for untrusted Markdown. When enabled it:
- blocks dangerous URL schemes (
javascript:, vbscript:, data: — except data:image/... for image src) in generated links/images, resolving obfuscations (entities, control characters) before checking; and
- escapes all raw HTML tags and strips inline event-handler attributes (
onerror, onload, onclick, …), so embedded <script>, <img onerror=…> and <svg onload=…> cannot execute.
⚠️ safeMode is defense-in-depth, not a full HTML sanitizer. For fully untrusted input, still run the output through a dedicated sanitizer such as DOMPurify and serve a Content-Security-Policy. (since v3.0.0)
disallowRawHTML: (boolean) [default false] Applies the GFM "disallowed raw HTML" tagfilter, escaping the leading < of a small blacklist (title, textarea, style, xmp, iframe, noembed, noframes, script, plaintext). This is a narrow GFM-compatibility filter — it does not block event handlers, javascript: URLs, <svg>, etc. Use safeMode for broader hardening.
CommonMark options (since v3.0.0)
These options make Showdown follow the CommonMark spec. They are
boolean and default to false, and are best enabled via the commonmark flavor. See the
Spec compliance docs for details.
- cmSpec: Enable CommonMark spec compliance — parse both block-level constructs (lists, block quotes, HTML blocks, container nesting, tab expansion) and inline constructs (emphasis, links, images, autolinks, raw HTML) per the CommonMark spec instead of Showdown's legacy matching. Most other options still apply on top (GFM extras like
ghMentions, simplifiedAutoLink, emoji, underline, tables, tasklists, parseImgDimensions, …); a few that tweak the replaced parsers are ignored (literalMidWordUnderscores, splitAdjacentBlockquotes, …). See the spec-compliance docs for the full list.
- decodeEntities: Resolve HTML5 named and numeric character references (
©, #, ಫ) to their characters. Kept separate from cmSpec because it is also useful on its own.
NOTE: In the CLI tool, all options are disabled by default — including those (like ghCodeBlocks) that are enabled by default in the Node and browser builds.
Flavors
You can also use flavors or presets to set the correct options automatically, so that showdown behaves like popular markdown flavors.
Currently, the following flavors are available:
- original - original markdown flavor as in John Gruber's spec
- vanilla - showdown base flavor (as from v1.3.1)
- gfm - GFM (GitHub Flavored Markdown);
github is a backwards-compatible alias
- commonmark - CommonMark CommonMark flavor (as from v3.0.0)
Global
showdown.setFlavor('gfm');
Instance
converter.setFlavor('gfm');
Showdown also comes bundled with a Command Line Interface tool. You can check the CLI wiki page for more info
Integration with AngularJS
ShowdownJS project also provides seamlessly integration with AngularJS via a "plugin".
Please visit https://github.com/showdownjs/ngShowdown for more information.
Integration with TypeScript
If you're using TypeScript you maybe want to use the types from DefinitelyTyped
Integration with SystemJS/JSPM
Integration with SystemJS can be obtained via the third party "system-md" plugin.
Integration with VueJS
To use ShowdownJS as a Vue component quickly, you can check vue-showdown.
XSS vulnerability
Showdown doesn't sanitize the input. This is by design since markdown relies on it to allow certain features to be correctly parsed into HTML.
This, however, means XSS injection is quite possible.
If your Markdown source is untrusted, you should:
- Enable the safeMode option — it blocks dangerous URL schemes (
javascript:, etc.) and escapes raw HTML tags / event handlers as defense-in-depth; and
- Run the generated HTML through a dedicated sanitizer such as DOMPurify before inserting it into the DOM, and serve a Content-Security-Policy.
safeMode is not a full HTML sanitizer and does not replace this step; and
- Cap the size of untrusted input (and/or convert off the request thread with a timeout) — converting very large adversarial inputs can be CPU-intensive.
Please refer to the wiki article Markdown's XSS Vulnerability (and how to mitigate it)
for more information.
Extensions
Showdown allows additional functionality to be loaded via extensions. (you can find a list of known showdown extensions here)
You can also find a boilerplate, to create your own extensions in this repository
Client-side Extension Usage
<script src="showdown.js" />
<script src="twitter-extension.js" />
var converter = new showdown.Converter({ extensions: ['twitter'] });
Server-side Extension Usage
var showdown = require('showdown'),
myExtension = require('myExtension'),
converter = new showdown.Converter({ extensions: ['myExtension'] });
Building
Building your clone of the repository is easy.
Prerequesites: a currently supported Node.js, npm and npx must be installed.
run npm install.
run npx grunt build (see Gruntfile.js). This command:
- Cleans the repo.
- Checks code quality (JSHint and ESLint).
- Runs tests.
- Creates the distributable and minified files in the
dist folder.
Tests
A suite of tests is available which require Node.js. Once Node is installed, run the following command from
the project root to install the dependencies:
npm install
Once installed the tests can be run from the project root using:
npm test
New test cases can easily be added. Create a markdown file (ending in .md) which contains the markdown to test.
Create a .html file of the exact same name. It will automatically be tested when the tests are executed with mocha.
Contributing
If you wish to contribute please read the following quick guide.
Want a Feature?
You can request a new feature by submitting an issue. If you would like to implement a new feature feel free to issue a
Pull Request.
Pull requests (PRs)
PRs are awesome. However, before you submit your pull request consider the following guidelines:
Search GitHub for an open or closed Pull Request that relates to your submission. You don't want to duplicate effort.
When issuing PRs that change code, make your changes in a new git branch based on develop:
git checkout -b my-fix-branch develop
Run the full test suite before submitting and make sure all tests pass (obviously =P).
Try to follow our coding style rules. Breaking them prevents the PR to pass the tests.
Refrain from fixing multiple issues in the same pull request. It's preferable to open multiple small PRs instead of one
hard to review big one.
If the PR introduces a new feature or fixes an issue, please add the appropriate test case.
We use conventional commit notes to generate the changelog that follow the conventional changelog spec. It's extremely helpful if your commit messages adhere to these Commit Guidelines.
Don't forget to add your name to the CREDITS.md file. We like to give credit were it's due.
If we suggest changes then:
- Make the required updates.
- Re-run the test suite to ensure tests are still passing.
- Rebase your branch and force push to your GitHub repository (this will update your Pull Request):
git rebase develop -i
git push origin my-fix-branch -f
After your pull request is merged, you can safely delete your branch.
If you have time to contribute to this project, we feel obliged that you get credit for it.
These rules enable us to review your PR faster and will give you appropriate credit in your GitHub profile.
We thank you in advance for your contribution!
Joining the team
We're looking for members to help maintaining Showdown.
Please see this issue to express interest or comment on this note.
Credits
Full credit list at https://github.com/showdownjs/showdown/blob/master/CREDITS.md
Showdown is powered by:
Showdown is a JavaScript library that converts Markdown to HTML and HTML back to Markdown, bidirectionally.