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Rules

This document contains a description of all rules, what they are checking for, as well as an examples of documents that break the rule and corrected versions of the examples.

MD001 - Heading levels should only increment by one level at a time

Tags: headings, headers

Aliases: heading-increment, header-increment

This rule is triggered when you skip heading levels in a markdown document, for example:

# Heading 1

### Heading 3

We skipped out a 2nd level heading in this document

When using multiple heading levels, nested headings should increase by only one level at a time:

# Heading 1

## Heading 2

### Heading 3

#### Heading 4

## Another Heading 2

### Another Heading 3

MD002 - First heading should be a top level heading

Tags: headings, headers

Aliases: first-heading-h1, first-header-h1

Parameters: level (number; default 1)

This rule is triggered when the first heading in the document isn't a h1 heading:

## This isn't a H1 heading

### Another heading

The first heading in the document should be a h1 heading:

# Start with a H1 heading

## Then use a H2 for subsections

Note: The level parameter can be used to change the top level (ex: to h2) in cases where an h1 is added externally.

MD003 - Heading style

Tags: headings, headers

Aliases: heading-style, header-style

Parameters: style ("consistent", "atx", "atx_closed", "setext", "setext_with_atx", "setext_with_atx_closed"; default "consistent")

This rule is triggered when different heading styles (atx, setext, and 'closed' atx) are used in the same document:

# ATX style H1

## Closed ATX style H2 ##

Setext style H1
===============

Be consistent with the style of heading used in a document:

# ATX style H1

## ATX style H2

The setext_with_atx and setext_with_atx_closed doc styles allow atx-style headings of level 3 or more in documents with setext style headings:

Setext style H1
===============

Setext style H2
---------------

### ATX style H3

Note: the configured heading style can be a specific style to use (atx, atx_closed, setext, setext_with_atx, setext_with_atx_closed), or simply require that the usage be consistent within the document.

MD004 - Unordered list style

Tags: bullet, ul

Aliases: ul-style

Parameters: style ("consistent", "asterisk", "plus", "dash", "sublist"; default "consistent")

This rule is triggered when the symbols used in the document for unordered list items do not match the configured unordered list style:

* Item 1
+ Item 2
- Item 3

To fix this issue, use the configured style for list items throughout the document:

* Item 1
* Item 2
* Item 3

The configured list style can be a specific symbol to use (asterisk, plus, dash), can require that usage be consistent within the document, or can require that each sublist have a consistent symbol that is different from its parent list.

For example, the following is valid for the sublist style because the outer-most indent uses asterisk, the middle indent uses plus, and the inner-most indent uses dash:

* Item 1
  + Item 2
    - Item 3
  + Item 4
* Item 4
  + Item 5

MD005 - Inconsistent indentation for list items at the same level

Tags: bullet, ul, indentation

Aliases: list-indent

This rule is triggered when list items are parsed as being at the same level, but don't have the same indentation:

* Item 1
  * Nested Item 1
  * Nested Item 2
   * A misaligned item

Usually this rule will be triggered because of a typo. Correct the indentation for the list to fix it:

* Item 1
  * Nested Item 1
  * Nested Item 2
  * Nested Item 3

Sequentially-ordered list markers are usually left-aligned such that all items have the same starting column:

...
8. Item
9. Item
10. Item
11. Item
...

This rule also supports right-alignment of list markers such that all items have the same ending column:

...
 8. Item
 9. Item
10. Item
11. Item
...

MD006 - Consider starting bulleted lists at the beginning of the line

Tags: bullet, ul, indentation

Aliases: ul-start-left

This rule is triggered when top level lists don't start at the beginning of a line:

Some text

  * List item
  * List item

To fix, ensure that top level list items are not indented:

Some test

* List item
* List item

Rationale: Starting lists at the beginning of the line means that nested list items can all be indented by the same amount when an editor's indent function or the tab key is used to indent. Starting a list 1 space in means that the indent of the first nested list is less than the indent of the second level (3 characters if you use 4 space tabs, or 1 character if you use 2 space tabs).

Note: This rule is triggered for the following scenario because the unordered sublist is not recognized as such by the parser. Not being nested 3 characters as required by the outer ordered list, it creates a top-level unordered list instead.

1. List item
  - List item
  - List item
1. List item

MD007 - Unordered list indentation

Tags: bullet, ul, indentation

Aliases: ul-indent

Parameters: indent (number; default 2)

This rule is triggered when list items are not indented by the configured number of spaces (default: 2).

Example:

* List item
   * Nested list item indented by 3 spaces

Corrected Example:

* List item
  * Nested list item indented by 2 spaces

Rationale (2 space indent): indenting by 2 spaces allows the content of a nested list to be in line with the start of the content of the parent list when a single space is used after the list marker.

Rationale (4 space indent): Same indent as code blocks, simpler for editors to implement. See http://www.cirosantilli.com/markdown-styleguide/#indented-lists for more information.

In addition, this is a compatibility issue with multi-markdown parsers, which require a 4 space indents. See http://support.markedapp.com/discussions/problems/21-sub-lists-not-indenting for a description of the problem.

Note: This rule applies to a sublist only if its parent lists are all also unordered (otherwise, extra indentation of ordered lists interferes with the rule).

MD009 - Trailing spaces

Tags: whitespace

Aliases: no-trailing-spaces

Parameters: br_spaces, list_item_empty_lines (number; default 2, boolean; default false)

This rule is triggered on any lines that end with unexpected whitespace. To fix this, remove the trailing space from the end of the line.

The br_spaces parameter allows an exception to this rule for a specific number of trailing spaces, typically used to insert an explicit line break. The default value allows 2 spaces to indicate a hard break (<br> element).

Note: You must set br_spaces to a value >= 2 for this parameter to take effect. Setting br_spaces to 1 behaves the same as 0, disallowing any trailing spaces.

Using spaces to indent blank lines inside a list item is usually not necessary, but some parsers require it. Set the list_item_empty_lines parameter to true to allow this:

- list item text
  [2 spaces]
  list item text

MD010 - Hard tabs

Tags: whitespace, hard_tab

Aliases: no-hard-tabs

Parameters: code_blocks (boolean; default true)

This rule is triggered by any lines that contain hard tab characters instead of using spaces for indentation. To fix this, replace any hard tab characters with spaces instead.

Example:

Some text

	* hard tab character used to indent the list item

Corrected example:

Some text

    * Spaces used to indent the list item instead

You have the option to exclude this rule for code blocks. To do so, set the code_blocks parameter to false. Code blocks are included by default since handling of tabs by tools is often inconsistent (ex: using 4 vs. 8 spaces).

MD011 - Reversed link syntax

Tags: links

Aliases: no-reversed-links

This rule is triggered when text that appears to be a link is encountered, but where the syntax appears to have been reversed (the [] and () are reversed):

(Incorrect link syntax)[http://www.example.com/]

To fix this, swap the [] and () around:

[Correct link syntax](http://www.example.com/)

Note: Markdown Extra-style footnotes do not trigger this rule:

For (example)[^1]

MD012 - Multiple consecutive blank lines

Tags: whitespace, blank_lines

Aliases: no-multiple-blanks

Parameters: maximum (number; default 1)

This rule is triggered when there are multiple consecutive blank lines in the document:

Some text here


Some more text here

To fix this, delete the offending lines:

Some text here

Some more text here

Note: this rule will not be triggered if there are multiple consecutive blank lines inside code blocks.

Note: The maximum parameter can be used to configure the maximum number of consecutive blank lines.

MD013 - Line length

Tags: line_length

Aliases: line-length

Parameters: line_length, code_blocks, tables, headings, headers (number; default 80, boolean; default true)

If headings is not provided, headers (deprecated) will be used.

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You have the option to exclude this rule for code blocks, tables, or headings. To do so, set the code_blocks, tables, or headings parameter(s) to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD014 - Dollar signs used before commands without showing output

Tags: code

Aliases: commands-show-output

This rule is triggered when there are code blocks showing shell commands to be typed, and the shell commands are preceded by dollar signs ($):

$ ls
$ cat foo
$ less bar

The dollar signs are unnecessary in the above situation, and should not be included:

ls
cat foo
less bar

However, an exception is made when there is a need to distinguish between typed commands and command output, as in the following example:

$ ls
foo bar
$ cat foo
Hello world
$ cat bar
baz

Rationale: it is easier to copy and paste and less noisy if the dollar signs are omitted when they are not needed. See http://www.cirosantilli.com/markdown-styleguide/#dollar-signs-in-shell-code for more information.

MD018 - No space after hash on atx style heading

Tags: headings, headers, atx, spaces

Aliases: no-missing-space-atx

This rule is triggered when spaces are missing after the hash characters in an atx style heading:

#Heading 1

##Heading 2

To fix this, separate the heading text from the hash character by a single space:

# Heading 1

## Heading 2

MD019 - Multiple spaces after hash on atx style heading

Tags: headings, headers, atx, spaces

Aliases: no-multiple-space-atx

This rule is triggered when more than one space is used to separate the heading text from the hash characters in an atx style heading:

#  Heading 1

##  Heading 2

To fix this, separate the heading text from the hash character by a single space:

# Heading 1

## Heading 2

MD020 - No space inside hashes on closed atx style heading

Tags: headings, headers, atx_closed, spaces

Aliases: no-missing-space-closed-atx

This rule is triggered when spaces are missing inside the hash characters in a closed atx style heading:

#Heading 1#

##Heading 2##

To fix this, separate the heading text from the hash character by a single space:

# Heading 1 #

## Heading 2 ##

Note: this rule will fire if either side of the heading is missing spaces.

MD021 - Multiple spaces inside hashes on closed atx style heading

Tags: headings, headers, atx_closed, spaces

Aliases: no-multiple-space-closed-atx

This rule is triggered when more than one space is used to separate the heading text from the hash characters in a closed atx style heading:

#  Heading 1  #

##  Heading 2  ##

To fix this, separate the heading text from the hash character by a single space:

# Heading 1 #

## Heading 2 ##

Note: this rule will fire if either side of the heading contains multiple spaces.

MD022 - Headings should be surrounded by blank lines

Tags: headings, headers, blank_lines

Aliases: blanks-around-headings, blanks-around-headers

This rule is triggered when headings (any style) are either not preceded or not followed by a blank line:

# Heading 1
Some text

Some more text
## Heading 2

To fix this, ensure that all headings have a blank line both before and after (except where the heading is at the beginning or end of the document):

# Heading 1

Some text

Some more text

## Heading 2

Rationale: Aside from aesthetic reasons, some parsers, including kramdown, will not parse headings that don't have a blank line before, and will parse them as regular text.

MD023 - Headings must start at the beginning of the line

Tags: headings, headers, spaces

Aliases: heading-start-left, header-start-left

This rule is triggered when a heading is indented by one or more spaces:

Some text

  # Indented heading

To fix this, ensure that all headings start at the beginning of the line:

Some text

# Heading

Rationale: Headings that don't start at the beginning of the line will not be parsed as headings, and will instead appear as regular text.

MD024 - Multiple headings with the same content

Tags: headings, headers

Aliases: no-duplicate-heading, no-duplicate-header

Parameters: siblings_only, allow_different_nesting (boolean; default false)

This rule is triggered if there are multiple headings in the document that have the same text:

# Some text

## Some text

To fix this, ensure that the content of each heading is different:

# Some text

## Some more text

Rationale: Some markdown parses generate anchors for headings based on the heading name, and having headings with the same content can cause problems with this.

If the parameter siblings_only (alternatively allow_different_nesting) is set to true, heading duplication is allowed for non-sibling headings (common in change logs):

# Change log

## 1.0.0

### Features

## 2.0.0

### Features

MD025 - Multiple top level headings in the same document

Tags: headings, headers

Aliases: single-h1

Parameters: level (number; default 1)

This rule is triggered when a top level heading is in use (the first line of the file is a h1 heading), and more than one h1 heading is in use in the document:

# Top level heading

# Another top level heading

To fix, structure your document so that there is a single h1 heading that is the title for the document, and all later headings are h2 or lower level headings:

# Title

## Heading

## Another heading

Rationale: A top level heading is a h1 on the first line of the file, and serves as the title for the document. If this convention is in use, then there can not be more than one title for the document, and the entire document should be contained within this heading.

Note: The level parameter can be used to change the top level (ex: to h2) in cases where an h1 is added externally.

MD026 - Trailing punctuation in heading

Tags: headings, headers

Aliases: no-trailing-punctuation

Parameters: punctuation (string; default ".,;:!?")

This rule is triggered on any heading that has a punctuation character as the last character in the line:

# This is a heading.

To fix this, remove any trailing punctuation:

# This is a heading

Note: The punctuation parameter can be used to specify what characters class as punctuation at the end of the heading. For example, you can set it to ".,;:!" to allow headings with question marks in them, such as might be used in an FAQ.

MD027 - Multiple spaces after blockquote symbol

Tags: blockquote, whitespace, indentation

Aliases: no-multiple-space-blockquote

This rule is triggered when blockquotes have more than one space after the blockquote (>) symbol:

>  This is a block quote with bad indentation
>  there should only be one.

To fix, remove any extraneous space:

> This is a blockquote with correct
> indentation.

MD028 - Blank line inside blockquote

Tags: blockquote, whitespace

Aliases: no-blanks-blockquote

This rule is triggered when two blockquote blocks are separated by nothing except for a blank line:

> This is a blockquote
> which is immediately followed by

> this blockquote. Unfortunately
> In some parsers, these are treated as the same blockquote.

To fix this, ensure that any blockquotes that are right next to each other have some text in between:

> This is a blockquote.

And Jimmy also said:

> This too is a blockquote.

Alternatively, if they are supposed to be the same quote, then add the blockquote symbol at the beginning of the blank line:

> This is a blockquote.
>
> This is the same blockquote.

Rationale: Some markdown parsers will treat two blockquotes separated by one or more blank lines as the same blockquote, while others will treat them as separate blockquotes.

MD029 - Ordered list item prefix

Tags: ol

Aliases: ol-prefix

Parameters: style ("one", "ordered", "one_or_ordered"; default "one_or_ordered")

This rule is triggered on ordered lists that do not either start with '1.' or do not have a prefix that increases in numerical order (depending on the configured style).

Example valid list if the style is configured as 'one':

1. Do this.
1. Do that.
1. Done.

Example valid list if the style is configured as 'ordered':

1. Do this.
2. Do that.
3. Done.

Both examples are valid when the style is configured as 'one_or_ordered'.

Example invalid list for all styles:

1. Do this.
3. Done.

This rule supports 0-prefixing ordered list items for uniform indentation:

...
08. Item
09. Item
10. Item
11. Item
...

MD030 - Spaces after list markers

Tags: ol, ul, whitespace

Aliases: list-marker-space

Parameters: ul_single, ol_single, ul_multi, ol_multi (number; default 1)

This rule checks for the number of spaces between a list marker (e.g. '-', '*', '+' or '1.') and the text of the list item.

The number of spaces checked for depends on the document style in use, but the default is 1 space after any list marker:

* Foo
* Bar
* Baz

1. Foo
1. Bar
1. Baz

1. Foo
   * Bar
1. Baz

A document style may change the number of spaces after unordered list items and ordered list items independently, as well as based on whether the content of every item in the list consists of a single paragraph, or multiple paragraphs (including sub-lists and code blocks).

For example, the style guide at http://www.cirosantilli.com/markdown-styleguide/#spaces-after-marker specifies that 1 space after the list marker should be used if every item in the list fits within a single paragraph, but to use 2 or 3 spaces (for ordered and unordered lists respectively) if there are multiple paragraphs of content inside the list:

* Foo
* Bar
* Baz

vs.

*   Foo

    Second paragraph

*   Bar

or

1.  Foo

    Second paragraph

1.  Bar

To fix this, ensure the correct number of spaces are used after list marker for your selected document style.

MD031 - Fenced code blocks should be surrounded by blank lines

Tags: code, blank_lines

Aliases: blanks-around-fences

This rule is triggered when fenced code blocks are either not preceded or not followed by a blank line:

Some text
```
Code block
```

```
Another code block
```
Some more text

To fix this, ensure that all fenced code blocks have a blank line both before and after (except where the block is at the beginning or end of the document):

Some text

```
Code block
```

```
Another code block
```

Some more text

Rationale: Aside from aesthetic reasons, some parsers, including kramdown, will not parse fenced code blocks that don't have blank lines before and after them.

MD032 - Lists should be surrounded by blank lines

Tags: bullet, ul, ol, blank_lines

Aliases: blanks-around-lists

This rule is triggered when lists (of any kind) are either not preceded or not followed by a blank line:

Some text
* Some
* List

1. Some
2. List
Some text

To fix this, ensure that all lists have a blank line both before and after (except where the block is at the beginning or end of the document):

Some text

* Some
* List

1. Some
2. List

Some text

Rationale: Aside from aesthetic reasons, some parsers, including kramdown, will not parse lists that don't have blank lines before and after them.

Note: List items without hanging indents are a violation of this rule; list items with hanging indents are okay:

* This is
not okay

* This is
  okay

MD033 - Inline HTML

Tags: html

Aliases: no-inline-html

Parameters: allowed_elements (array of string; default empty)

This rule is triggered whenever raw HTML is used in a markdown document:

<h1>Inline HTML heading</h1>

To fix this, use 'pure' markdown instead of including raw HTML:

# Markdown heading

Rationale: Raw HTML is allowed in markdown, but this rule is included for those who want their documents to only include "pure" markdown, or for those who are rendering markdown documents in something other than HTML.

Note: To allow specific HTML elements, use the 'allowed_elements' parameter.

MD034 - Bare URL used

Tags: links, url

Aliases: no-bare-urls

This rule is triggered whenever a URL is given that isn't surrounded by angle brackets:

For more information, see http://www.example.com/.

To fix this, add angle brackets around the URL:

For more information, see <http://www.example.com/>.

Rationale: Without angle brackets, the URL isn't converted into a link in many markdown parsers.

Note: if you do want a bare URL without it being converted into a link, enclose it in a code block, otherwise in some markdown parsers it will be converted:

`http://www.example.com`

MD035 - Horizontal rule style

Tags: hr

Aliases: hr-style

Parameters: style ("consistent", "---", "***", or other string specifying the horizontal rule; default "consistent")

This rule is triggered when inconsistent styles of horizontal rules are used in the document:

---

- - -

***

* * *

****

To fix this, ensure any horizontal rules used in the document are consistent, or match the given style if the rule is so configured:

---

---

Note: by default, this rule is configured to just require that all horizontal rules in the document are the same, and will trigger if any of the horizontal rules are different than the first one encountered in the document. If you want to configure the rule to match a specific style, the parameter given to the 'style' option is a string containing the exact horizontal rule text that is allowed.

MD036 - Emphasis used instead of a heading

Tags: headings, headers, emphasis

Aliases: no-emphasis-as-heading, no-emphasis-as-header

Parameters: punctuation (string; default ".,;:!?")

This check looks for instances where emphasized (i.e. bold or italic) text is used to separate sections, where a heading should be used instead:

**My document**

Lorem ipsum dolor sit amet...

_Another section_

Consectetur adipiscing elit, sed do eiusmod.

To fix this, use markdown headings instead of emphasized text to denote sections:

# My document

Lorem ipsum dolor sit amet...

## Another section

Consectetur adipiscing elit, sed do eiusmod.

Note: this rule looks for single line paragraphs that consist entirely of emphasized text. It won't fire on emphasis used within regular text, multi-line emphasized paragraphs, and paragraphs ending in punctuation. Similarly to rule MD026, you can configure what characters are recognized as punctuation.

MD037 - Spaces inside emphasis markers

Tags: whitespace, emphasis

Aliases: no-space-in-emphasis

This rule is triggered when emphasis markers (bold, italic) are used, but they have spaces between the markers and the text:

Here is some ** bold ** text.

Here is some * italic * text.

Here is some more __ bold __ text.

Here is some more _ italic _ text.

To fix this, remove the spaces around the emphasis markers:

Here is some **bold** text.

Here is some *italic* text.

Here is some more __bold__ text.

Here is some more _italic_ text.

Rationale: Emphasis is only parsed as such when the asterisks/underscores aren't completely surrounded by spaces. This rule attempts to detect where they were surrounded by spaces, but it appears that emphasized text was intended by the author.

MD038 - Spaces inside code span elements

Tags: whitespace, code

Aliases: no-space-in-code

This rule is triggered on code span elements that have spaces right inside the backticks:

` some text `

`some text `

` some text`

To fix this, remove the spaces inside the codespan markers:

`some text`

Note: A single leading or trailing space is allowed if used to separate codespan markers from an embedded backtick:

`` ` embedded backtick``

MD039 - Spaces inside link text

Tags: whitespace, links

Aliases: no-space-in-links

This rule is triggered on links that have spaces surrounding the link text:

[ a link ](http://www.example.com/)

To fix this, remove the spaces surrounding the link text:

[a link](http://www.example.com/)

MD040 - Fenced code blocks should have a language specified

Tags: code, language

Aliases: fenced-code-language

This rule is triggered when fenced code blocks are used, but a language isn't specified:

```
#!/bin/bash
echo Hello world
```

To fix this, add a language specifier to the code block:

```bash
#!/bin/bash
echo Hello world
```

MD041 - First line in file should be a top level heading

Tags: headings, headers

Aliases: first-line-h1

Parameters: level, front_matter_title (number; default 1, string; default "^\s*title:")

This rule is triggered when the first line in the file isn't a top level (h1) heading:

This is a file without a heading

To fix this, add a heading to the top of your file:

# File with heading

This is a file with a top level heading

The level parameter can be used to change the top level (ex: to h2) in cases where an h1 is added externally.

If front matter is present and contains a YAML title property (commonly used with blog posts), this rule will not report a violation. To use a different property name in front matter, specify the text of a regular expression via the front_matter_title parameter. To disable the use of front matter by this rule, specify "" for front_matter_title.

MD042 - No empty links

Tags: links

Aliases: no-empty-links

This rule is triggered when an empty link is encountered:

[an empty link]()

To fix the violation, provide a destination for the link:

[a valid link](https://example.com/)

Empty fragments will trigger this rule:

[an empty fragment](#)

But non-empty fragments will not:

[a valid fragment](#fragment)

MD043 - Required heading structure

Tags: headings, headers

Aliases: required-headings, required-headers

Parameters: headings, headers (array of string; default null for disabled)

If headings is not provided, headers (deprecated) will be used.

This rule is triggered when the headings in a file do not match the array of headings passed to the rule. It can be used to enforce a standard heading structure for a set of files.

To require exactly the following structure:

# Head
## Item
### Detail

Set the headings parameter to:

[
    "# Head",
    "## Item",
    "### Detail"
]

To allow optional headings as with the following structure:

# Head
## Item
### Detail (optional)
## Foot
### Notes (optional)

Use the special value "*" meaning "one or more unspecified headings" and set the headings parameter to:

[
    "# Head",
    "## Item",
    "*",
    "## Foot",
    "*"
]

When an error is detected, this rule outputs the line number of the first problematic heading (otherwise, it outputs the last line number of the file).

Note that while the headings parameter uses the "## Text" ATX heading style for simplicity, a file may use any supported heading style.

MD044 - Proper names should have the correct capitalization

Tags: spelling

Aliases: proper-names

Parameters: names, code_blocks (string array; default null, boolean; default true)

This rule is triggered when any of the strings in the names array do not have the specified capitalization. It can be used to enforce a standard letter case for the names of projects and products.

For example, the language "JavaScript" is usually written with both the 'J' and 'S' capitalized - though sometimes the 's' or 'j' appear in lower-case. To enforce the proper capitalization, specify the desired letter case in the names array:

[
    "JavaScript"
]

Set the code_blocks parameter to false to disable this rule for code blocks.

MD045 - Images should have alternate text (alt text)

Tags: accessibility, images

Aliases: no-alt-text

This rule is triggered when an image is missing alternate text (alt text) information. Alternate text is important for accessibility, describing the content of an image for people who may not be able to see it.

Alternate text is commonly specified inline as:

![Alternate text](image.jpg)

Or with reference syntax as:

![Alternate text][ref]

...

[ref]: image.jpg "Optional title"

Guidance for writing alternate text is available from the W3C, Wikipedia, and other locations.