[syntax] Comments in Markdown

How do you write a comment in Markdown, i.e. text that is not rendered in the HTML output? I found nothing on the Markdown project.

This works on GitHub:

[](Comment text goes here)

The resulting HTML looks like:

<a href="Comment%20text%20goes%20here"></a>

Which is basically an empty link. Obviously you can read that in the source of the rendered text, but you can do that on GitHub anyway.

<!--- ... --> 

Does not work in Pandoc Markdown (Pandoc 1.12.2.1). Comments still appeared in html. The following did work:

Blank line
[^Comment]:  Text that will not appear in html source
Blank line

Then use the +footnote extension. It is essentially a footnote that never gets referenced.

An alternative is to put comments within stylized HTML tags. This way, you can toggle their visibility as needed. For example, define a comment class in your CSS stylesheet.

.comment { display: none; }

Then, the following enhanced MARKDOWN

We do <span class="comment">NOT</span> support comments

appears as follows in a BROWSER

We do support comments

I use standard HTML tags, like

<!---
your comment goes here
and here
-->

Note the triple dash. The advantage is that it works with pandoc when generating TeX or HTML output. More information is available on the pandoc-discuss group.

How about putting the comments in a non-eval, non-echo R block? i.e.,

```{r echo=FALSE, eval=FALSE}
All the comments!
```

Seems to work well for me.

You can try

[](
Your comments go here however you cannot leave
// a blank line so fill blank lines with
//
Something
)

kramdown—the Ruby-based markdown engine that is the default for Jekyll and thus GitHub Pages—has built-in comment support through its extension syntax:

{::comment}
This text is completely ignored by kramdown - a comment in the text.
{:/comment}

Do you see {::comment}this text{:/comment}?
{::comment}some other comment{:/}

This has the benefit of allowing in-line comments, but the downside of not being portable to other Markdown engines.

You can do this (YAML block):

~~~
# This is a
# multiline
# comment
...

I tried with latex output only, please confirm for others.

This small research proves and refines the answer by Magnus

The most platform-independent syntax is

(empty line)
[comment]: # (This actually is the most platform independent comment)

Both conditions are important:

1. Using # (and not <>)
2. With an empty line before the comment. Empty line after the comment has no impact on the result.

The strict Markdown specification CommonMark only works as intended with this syntax (and not with <> and/or an empty line)

To prove this we shall use the Babelmark2, written by John MacFarlane. This tool checks the rendering of particular source code in 28 Markdown implementations.

(+ — passed the test, - — didn't pass, ? — leaves some garbage which is not shown in rendered HTML).

• No empty lines, using <> 13+, 15-
• Empty line before the comment, using <> 20+, 8-
• Empty lines around the comment, using <> 20+, 8-
• No empty lines, using # 13+ 1? 14-
• Empty line before the comment, using # 23+ 1? 4-
• Empty lines around the comment, using # 23+ 1? 4-
• HTML comment with 3 hyphens 1+ 2? 25- from the chl's answer (note that this is different syntax)

This proves the statements above.

These implementations fail all 7 tests. There's no chance to use excluded-on-render comments with them.

• cebe/markdown 1.1.0
• cebe/markdown MarkdownExtra 1.1.0
• cebe/markdown GFM 1.1.0
• s9e\TextFormatter (Fatdown/PHP)

Vim Instant-Markdown users need to use

<!---
First comment line...
//
_NO_BLANK_LINES_ARE_ALLOWED_
//
_and_try_to_avoid_double_minuses_like_this_: --
//
last comment line.
-->

For pandoc, a good way to block comment is to use a yaml metablock, as suggested by the pandoc author. I have noticed that this gives more proper syntax highlighting of the comments compared to many of the other proposed solutions, at least in my environment (vim, vim-pandoc, and vim-pandoc-syntax).

I use yaml block comments in combination with html-inline comments, since html-comments cannot be nested. Unfortunately, there is no way of block commenting within the yaml metablock, so every line has to be commented individually. Fortunately, there should only be one line in a softwrapped paragraph.

In my ~/.vimrc, I have set up custom shortcuts for block comments:

nmap <Leader>b }o<Esc>O...<Esc>{ji#<Esc>O---<Esc>2<down>
nmap <Leader>v {jddx}kdd

I use , as my <Leader>-key, so ,b and ,v comment and uncomment a paragraph, respectively. If I need to comment multiple paragraphs, I map j,b to a macro (usually Q) and run <number-of-paragraphs><name-of-macro> (e.g. (3Q). The same works for uncommenting.

If you are using Jekyll or octopress following will also work.

{% comment %} 
    These commments will not include inside the source.
{% endcomment %}

The Liquid tags {% comment %} are parsed first and removed before the MarkDown processor even gets to it. Visitors will not see when they try to view source from their browser.

Disclosure: I wrote the plugin.

Since the question doesn't specify a specific markdown implementation I'd like to mention the Comments Plugin for python-markdown, which implements the same pandoc commenting style mentioned above.

The following works very well

<empty line>
[whatever comment text]::

that method takes advantage of syntax to create links via reference
since link reference created with [1]: http://example.org will not be rendered, likewise any of the following will not be rendered as well

<empty line>
[whatever]::
[whatever]:whatever
[whatever]: :
[whatever]: whatever

Also see Critic Markup, supported by an increasing number of Markdown tools.

http://criticmarkup.com/

Comment {>> <<}

Lorem ipsum dolor sit amet.{>>This is a comment<<}

Highlight+Comment {== ==}{>> <<}

Lorem ipsum dolor sit amet, consectetur adipiscing elit. {==Vestibulum at orci magna. Phasellus augue justo, sodales eu pulvinar ac, vulputate eget nulla.==}{>>confusing<<} Mauris massa sem, tempor sed cursus et, semper tincidunt lacus.