We specialize in Products, Application and Infrastructure security assessments and deep technical security training.



[![Build Status][BuildSVG]][BuildURL]



Blackfriday is a [Markdown][1] processor implemented in [Go][2]. It

is paranoid about its input (so you can safely feed it user-supplied

data), it is fast, it supports common extensions (tables, smart

punctuation substitutions, etc.), and it is safe for all utf-8

(unicode) input.

HTML output is currently supported, along with Smartypants


It started as a translation from C of [Sundown][3].


Blackfriday is compatible with any modern Go release. With Go and git installed:

go get -u

will download, compile, and install the package into your $GOPATH directory



Currently maintained and recommended version of Blackfriday is v2. It's being

developed on its own branch: and the

documentation is available at

It is go get-able via [][6] at,

but we highly recommend using package management tool like [dep][7] or

[Glide][8] and make use of semantic versioning. With package management you

should import and specify that you're using

version 2.0.0.

Version 2 offers a number of improvements over v1:

  • Cleaned up API
  • A separate call to [Parse][4], which produces an abstract syntax tree for

the document

  • Latest bug fixes
  • Flexibility to easily add your own rendering extensions

Potential drawbacks:

  • Our benchmarks show v2 to be slightly slower than v1. Currently in the

ballpark of around 15%.

  • API breakage. If you can't afford modifying your code to adhere to the new API

and don't care too much about the new features, v2 is probably not for you.

  • Several bug fixes are trailing behind and still need to be forward-ported to

v2. See issue #348 for


If you are still interested in the legacy v1, you can import it from Documentation for the legacy v1 can be found


Known issue with dep

There is a known problem with using Blackfriday v1 transitively and dep.

Currently dep prioritizes semver versions over anything else, and picks the

latest one, plus it does not apply a [[constraint]] specifier to transitively

pulled in packages. So if you're using something that uses Blackfriday v1, but

that something does not use dep yet, you will get Blackfriday v2 pulled in and

your first dependency will fail to build.

There are couple of fixes for it, documented here:

Meanwhile, dep team is working on a more general solution to the constraints

on transitive dependencies problem:



For basic usage, it is as simple as getting your input into a byte

slice and calling:


output := blackfriday.MarkdownBasic(input)


This renders it with no extensions enabled. To get a more useful

feature set, use this instead:


output := blackfriday.MarkdownCommon(input)



For the most sensible markdown processing, it is as simple as getting your input

into a byte slice and calling:


output := blackfriday.Run(input)


Your input will be parsed and the output rendered with a set of most popular

extensions enabled. If you want the most basic feature set, corresponding with

the bare Markdown specification, use:


output := blackfriday.Run(input, blackfriday.WithNoExtensions())


Sanitize untrusted content

Blackfriday itself does nothing to protect against malicious content. If you are

dealing with user-supplied markdown, we recommend running Blackfriday's output

through HTML sanitizer such as [Bluemonday][5].

Here's an example of simple usage of Blackfriday together with Bluemonday:


import (



// ...

unsafe := blackfriday.Run(input)

html := bluemonday.UGCPolicy().SanitizeBytes(unsafe)


Custom options, v1

If you want to customize the set of options, first get a renderer

(currently only the HTML output engine), then use it to

call the more general Markdown function. For examples, see the

implementations of MarkdownBasic and MarkdownCommon in


Custom options, v2

If you want to customize the set of options, use blackfriday.WithExtensions,

blackfriday.WithRenderer and blackfriday.WithRefOverride.


You can also check out blackfriday-tool for a more complete example

of how to use it. Download and install it using:

go get

This is a simple command-line tool that allows you to process a

markdown file using a standalone program. You can also browse the

source directly on github if you are just looking for some example


Note that if you have not already done so, installing

blackfriday-tool will be sufficient to download and install

blackfriday in addition to the tool itself. The tool binary will be

installed in $GOPATH/bin. This is a statically-linked binary that

can be copied to wherever you need it without worrying about

dependencies and library versions.

Sanitized anchor names

Blackfriday includes an algorithm for creating sanitized anchor names

corresponding to a given input text. This algorithm is used to create

anchors for headings when EXTENSION_AUTO_HEADER_IDS is enabled. The

algorithm has a specification, so that other packages can create

compatible anchor names and links to those anchors.

The specification is located at

SanitizedAnchorName exposes this functionality, and can be used to

create compatible links to the anchor names generated by blackfriday.

This algorithm is also implemented in a small standalone package at It can be useful for clients

that want a small package and don't need full functionality of blackfriday.


All features of Sundown are supported, including:

  • Compatibility. The Markdown v1.0.3 test suite passes with
the `--tidy` option.  Without `--tidy`, the differences are
mostly in whitespace and entity escaping, where blackfriday is
more consistent and cleaner.
  • Common extensions, including table support, fenced code
blocks, autolinks, strikethroughs, non-strict emphasis, etc.
  • Safety. Blackfriday is paranoid when parsing, making it safe
to feed untrusted user input without fear of bad things
happening. The test suite stress tests this and there are no
known inputs that make it crash.  If you find one, please let me
know and send me the input that does it.
NOTE: "safety" in this context means *runtime safety only*. In order to
protect yourself against JavaScript injection in untrusted content, see
[this example](
  • Fast processing. It is fast enough to render on-demand in
most web applications without having to cache the output.
  • Thread safety. You can run multiple parsers in different
goroutines without ill effect. There is no dependence on global
shared state.
  • Minimal dependencies. Blackfriday only depends on standard
library packages in Go. The source code is pretty
self-contained, so it is easy to add to any project, including
Google App Engine projects.
  • Standards compliant. Output successfully validates using the
W3C validation tool for HTML 4.01 and XHTML 1.0 Transitional.


In addition to the standard markdown syntax, this package

implements the following extensions:

  • Intra-word emphasis supression. The _ character is
commonly used inside words when discussing code, so having
markdown interpret it as an emphasis command is usually the
wrong thing. Blackfriday lets you treat all emphasis markers as
normal characters when they occur inside a word.
  • Tables. Tables can be created by drawing them in the input
using a simple syntax:
Name    | Age
Bob     | 27
Alice   | 23
  • Fenced code blocks. In addition to the normal 4-space
indentation to mark code blocks, you can explicitly mark them
and supply a language (to make syntax highlighting simple). Just
mark it like this:
    ``` go
    func getTrue() bool {
        return true
You can use 3 or more backticks to mark the beginning of the
block, and the same number to mark the end of the block.
To preserve classes of fenced code blocks while using the bluemonday
HTML sanitizer, use the following policy:
``` go
p := bluemonday.UGCPolicy()
html := p.SanitizeBytes(unsafe)
  • Definition lists. A simple definition list is made of a single-line
term followed by a colon and the definition for that term.
    : Fluffy animal everyone likes
    : Vector of transmission for pictures of cats
Terms must be separated from the previous definition by a blank line.
  • Footnotes. A marker in the text that will become a superscript number;
a footnote definition that will be placed in a list of footnotes at the
end of the document. A footnote looks like this:
    This is a footnote.[^1]
    [^1]: the footnote text.
  • Autolinking. Blackfriday can find URLs that have not been
explicitly marked as links and turn them into links.
  • Strikethrough. Use two tildes (~~) to mark text that
should be crossed out.
  • Hard line breaks. With this extension enabled (it is off by
default in the `MarkdownBasic` and `MarkdownCommon` convenience
functions), newlines in the input translate into line breaks in
the output.
  • Smart quotes. Smartypants-style punctuation substitution is
supported, turning normal double- and single-quote marks into
curly quotes, etc.
  • LaTeX-style dash parsing is an additional option, where --
is translated into `–`, and `---` is translated into
`—`. This differs from most smartypants processors, which
turn a single hyphen into an ndash and a double hyphen into an
  • Smart fractions, where anything that looks like a fraction
is translated into suitable HTML (instead of just a few special
cases like most smartypant processors). For example, `4/5`
becomes `<sup>4</sup>&frasl;<sub>5</sub>`, which renders as

Other renderers

Blackfriday is structured to allow alternative rendering engines. Here

are a few of note:

provides a GitHub Flavored Markdown renderer with fenced code block
highlighting, clickable heading anchor links.
It's not customizable, and its goal is to produce HTML output
equivalent to the [GitHub Markdown API endpoint](,
except the rendering is performed locally.
but for markdown.
renders output as LaTeX.
integration with the [Chroma]( code
highlighting library. bfchroma is only compatible with v2 of Blackfriday and
provides a drop-in renderer ready to use with Blackfriday, as well as
options and means for further customization.


  • More unit testing
  • Improve Unicode support. It does not understand all Unicode
rules (about what constitutes a letter, a punctuation symbol,
etc.), so it may fail to detect word boundaries correctly in
some instances. It is safe on all UTF-8 input.


Blackfriday is distributed under the Simplified BSD License