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Rules

This document contains a description of all rules, what they are checking for, as well as examples of documents that break the rule and corrected versions of the examples. Any rule whose heading is struck through is deprecated, but still provided for backward-compatibility.

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

Tags: headers, headings

Aliases: header-increment, heading-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

Rationale: Headings represent the structure of a document and can be confusing when skipped - especially for accessibility scenarios. More information: https://www.w3.org/WAI/tutorials/page-structure/headings/.

MD002 - First heading should be a top-level heading

This rule is deprecated and provided for backward-compatibility

Tags: headers, headings

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

Parameters:

  • level: Heading level (integer, default 1)

Note: MD002 has been deprecated and is disabled by default. MD041/first-line-heading offers an improved implementation.

This rule is intended to ensure document headings start at the top level and is triggered when the first heading in the document isn't an h1 heading:

## This isn't an H1 heading

### Another heading

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

# Start with an H1 heading

## Then use an 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.

Rationale: The top-level heading often acts as the title of a document. More information: https://cirosantilli.com/markdown-style-guide#top-level-header.

MD003 - Heading style

Tags: headers, headings

Aliases: header-style, heading-style

Parameters:

  • style: Heading style (string, default consistent, values atx / atx_closed / consistent / setext / setext_with_atx / setext_with_atx_closed)

This rule is triggered when different heading styles are used in the same document:

# ATX style H1

## Closed ATX style H2 ##

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

To fix the issue, use consistent heading styles throughout the document:

# ATX style H1

## ATX style H2

The setext_with_atx and setext_with_atx_closed settings allow ATX-style headings of level 3 or more in documents with setext-style headings (which only support level 1 and 2 headings):

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

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

### ATX style H3

Note: The configured heading style can be a specific style to require (atx, atx_closed, setext, setext_with_atx, setext_with_atx_closed), or may just require that usage is consistent within the document via consistent.

Note: The placement of a horizontal rule directly below a line of text can trigger this rule by turning that text into a level 2 setext-style heading:

A line of text followed by a horizontal rule becomes a heading
---

Rationale: Consistent formatting makes it easier to understand a document.

MD004 - Unordered list style

Tags: bullet, ul

Aliases: ul-style

Parameters:

  • style: List style (string, default consistent, values asterisk / consistent / dash / plus / sublist)

Fixable: Some violations can be fixed by tooling

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), to ensure that all list styling is consistent, or to ensure that each sublist has a consistent symbol that differs 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

Rationale: Consistent formatting makes it easier to understand a document.

MD005 - Inconsistent indentation for list items at the same level

Tags: bullet, indentation, ul

Aliases: list-indent

Fixable: Some violations can be fixed by tooling

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
...

Rationale: Violations of this rule can lead to improperly rendered content.

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

This rule is deprecated and provided for backward-compatibility

Tags: bullet, indentation, ul

Aliases: ul-start-left

Fixable: Some violations can be fixed by tooling

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

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

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).

MD007 - Unordered list indentation

Tags: bullet, indentation, ul

Aliases: ul-indent

Parameters:

  • indent: Spaces for indent (integer, default 2)
  • start_indent: Spaces for first level indent (when start_indented is set) (integer, default 2)
  • start_indented: Whether to indent the first level of the list (boolean, default false)

Fixable: Some violations can be fixed by tooling

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

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).

The start_indented parameter allows the first level of lists to be indented by the configured number of spaces rather than starting at zero (the inverse of MD006). The start_indent parameter allows the first level of lists to be indented by a different number of spaces than the rest (ignored when start_indented is not set).

Rationale: 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. Indenting by 4 spaces is consistent with code blocks and simpler for editors to implement. Additionally, this can be a compatibility issue for other Markdown parsers, which require 4-space indents. More information: Markdown Style Guide and Marked app
support.

Note: See Prettier.md for compatibility information.

MD009 - Trailing spaces

Tags: whitespace

Aliases: no-trailing-spaces

Parameters:

  • br_spaces: Spaces for line break (integer, default 2)
  • list_item_empty_lines: Allow spaces for empty lines in list items (boolean, default false)
  • strict: Include unnecessary breaks (boolean, default false)

Fixable: Some violations can be fixed by tooling

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.

Note: Trailing space is allowed in indented and fenced code blocks because some languages require it.

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.

By default, this rule will not trigger when the allowed number of spaces is used, even when it doesn't create a hard break (for example, at the end of a paragraph). To report such instances as well, set the strict parameter to true.

Text text text
text[2 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 (even when strict is true):

- list item text
  [2 spaces]
  list item text

Rationale: Except when being used to create a line break, trailing whitespace has no purpose and does not affect the rendering of content.

MD010 - Hard tabs

Tags: hard_tab, whitespace

Aliases: no-hard-tabs

Parameters:

  • code_blocks: Include code blocks (boolean, default true)
  • ignore_code_languages: Fenced code languages to ignore (string[], default [])
  • spaces_per_tab: Number of spaces for each hard tab (integer, default 1)

Fixable: Some violations can be fixed by tooling

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 and spans. To do so, set the code_blocks parameter to false. Code blocks and spans are included by default since handling of tabs by Markdown tools can be inconsistent (e.g., using 4 vs. 8 spaces).

When code blocks are scanned (e.g., by default or if code_blocks is true), the ignore_code_languages parameter can be set to a list of languages that should be ignored (i.e., hard tabs will be allowed, though not required). This makes it easier for documents to include code for languages that require hard tabs.

By default, violations of this rule are fixed by replacing the tab with 1 space character. To use a different number of spaces, set the spaces_per_tab parameter to the desired value.

Rationale: Hard tabs are often rendered inconsistently by different editors and can be harder to work with than spaces.

MD011 - Reversed link syntax

Tags: links

Aliases: no-reversed-links

Fixable: Some violations can be fixed by tooling

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)[https://www.example.com/]

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

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

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

For (example)[^1]

Rationale: Reversed links are not rendered as usable links.

MD012 - Multiple consecutive blank lines

Tags: blank_lines, whitespace

Aliases: no-multiple-blanks

Parameters:

  • maximum: Consecutive blank lines (integer, default 1)

Fixable: Some violations can be fixed by tooling

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.

Rationale: Except in a code block, blank lines serve no purpose and do not affect the rendering of content.

MD013 - Line length

Tags: line_length

Aliases: line-length

Parameters:

  • code_block_line_length: Number of characters for code blocks (integer, default 80)
  • code_blocks: Include code blocks (boolean, default true)
  • headers: Include headings (boolean, default true)
  • heading_line_length: Number of characters for headings (integer, default 80)
  • headings: Include headings (boolean, default true)
  • line_length: Number of characters (integer, default 80)
  • stern: Stern length checking (boolean, default false)
  • strict: Strict length checking (boolean, default false)
  • tables: Include tables (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. To set a different maximum length for headings, use heading_line_length. To set a different maximum length for code blocks, use code_block_line_length

This rule has an exception when there is no whitespace beyond the configured line length. This allows you to include items such as long URLs without being forced to break them in the middle. To disable this exception, set the strict parameter to true and an issue will be reported when any line is too long. To warn for lines that are too long and could be fixed but allow long lines without spaces, set the stern parameter to true.

For example (assuming normal behavior):

IF THIS LINE IS THE MAXIMUM LENGTH
This line is okay because there are-no-spaces-beyond-that-length
And this line is a violation because there are
This-line-is-also-okay-because-there-are-no-spaces

In strict or stern modes, the two middle lines above are a violation. The third line is a violation in strict mode but allowed in stern mode.

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.

Lines with link/image reference definitions are always exempted from this rule (even in strict mode) because there is generally no way to split such lines without breaking the URL.

Rationale: Extremely long lines can be difficult to work with in some editors. More information: https://cirosantilli.com/markdown-style-guide#line-wrapping.

MD014 - Dollar signs used before commands without showing output

Tags: code

Aliases: commands-show-output

Fixable: Some violations can be fixed by tooling

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

$ ls
$ cat foo
$ less bar

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

ls
cat foo
less bar

Showing output for commands preceded by dollar signs does not trigger this rule:

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

Because some commands do not produce output, it is not a violation if some commands do not have output:

$ mkdir test
mkdir: created directory 'test'
$ ls test

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

MD018 - No space after hash on atx style heading

Tags: atx, headers, headings, spaces

Aliases: no-missing-space-atx

Fixable: Some violations can be fixed by tooling

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

Rationale: Violations of this rule can lead to improperly rendered content.

MD019 - Multiple spaces after hash on atx style heading

Tags: atx, headers, headings, spaces

Aliases: no-multiple-space-atx

Fixable: Some violations can be fixed by tooling

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

Rationale: Extra space has no purpose and does not affect the rendering of content.

MD020 - No space inside hashes on closed atx style heading

Tags: atx_closed, headers, headings, spaces

Aliases: no-missing-space-closed-atx

Fixable: Some violations can be fixed by tooling

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.

Rationale: Violations of this rule can lead to improperly rendered content.

MD021 - Multiple spaces inside hashes on closed atx style heading

Tags: atx_closed, headers, headings, spaces

Aliases: no-multiple-space-closed-atx

Fixable: Some violations can be fixed by tooling

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.

Rationale: Extra space has no purpose and does not affect the rendering of content.

MD022 - Headings should be surrounded by blank lines

Tags: blank_lines, headers, headings

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

Parameters:

  • lines_above: Blank lines above heading (integer, default 1)
  • lines_below: Blank lines below heading (integer, default 1)

Fixable: Some violations can be fixed by tooling

This rule is triggered when headings (any style) are either not preceded or not followed by at least one 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

The lines_above and lines_below parameters can be used to specify a different number of blank lines (including 0) above or below each heading.

Note: If lines_above or lines_below are configured to require more than one blank line, MD012/no-multiple-blanks should also be customized.

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: headers, headings, spaces

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

Fixable: Some violations can be fixed by tooling

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: headers, headings

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

Parameters:

  • allow_different_nesting: Only check sibling headings (boolean, default false)
  • siblings_only: Only check sibling headings (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

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

# Change log

## 1.0.0

### Features

## 2.0.0

### Features

Rationale: Some Markdown parsers generate anchors for headings based on the heading name; headings with the same content can cause problems with that.

MD025 - Multiple top-level headings in the same document

Tags: headers, headings

Aliases: single-h1, single-title

Parameters:

  • front_matter_title: RegExp for matching title in front matter (string, default ^\s*title\s*[:=])
  • level: Heading level (integer, default 1)

This rule is triggered when a top-level heading is in use (the first line of the file is an 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 there is a single h1 heading that is the title for the document. Subsequent headings must be lower-level headings (h2, h3, etc.):

# Title

## Heading

## Another heading

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

If YAML front matter is present and contains a title property (commonly used with blog posts), this rule treats that as a top level heading and will report a violation for any subsequent top-level headings. To use a different property name in the 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.

Rationale: A top-level heading is an 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.

MD026 - Trailing punctuation in heading

Tags: headers, headings

Aliases: no-trailing-punctuation

Parameters:

  • punctuation: Punctuation characters not allowed at end of headings (string, default .,;:!。，；：！)

Fixable: Some violations can be fixed by tooling

This rule is triggered on any heading that has one of the specified normal or full-width punctuation characters as the last character in the line:

# This is a heading.

To fix this, remove the trailing punctuation:

# This is a heading

Note: The punctuation parameter can be used to specify what characters count as punctuation at the end of a heading. For example, you can change it to ".,;:" to allow headings that end with an exclamation point. ? is allowed by default because of how common it is in headings of FAQ-style documents. Setting the punctuation parameter to "" allows all characters - and is equivalent to disabling the rule.

Note: The trailing semicolon of HTML entity references like &copy;, &#169;, and &#x000A9; is ignored by this rule.

Rationale: Headings are not meant to be full sentences. More information: Punctuation at the end of headers.

MD027 - Multiple spaces after blockquote symbol

Tags: blockquote, indentation, whitespace

Aliases: no-multiple-space-blockquote

Fixable: Some violations can be fixed by tooling

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

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

To fix, remove any extraneous space:

> This is a blockquote with correct
> indentation.

Rationale: Consistent formatting makes it easier to understand a document.

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: List style (string, default one_or_ordered, values one / one_or_ordered / ordered / zero)

This rule is triggered for 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). The less-common pattern of using '0.' as a first prefix or for all prefixes is also supported.

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

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

Examples of valid lists if the style is configured as 'ordered':

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

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

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

0. Do this.
0. Do that.
0. Done.

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
...

Note: This rule will report violations for cases like the following where an improperly-indented code block (or similar) appears between two list items and "breaks" the list in two:

1. First list

```text
Code block
```

1. Second list

The fix is to indent the code block so it becomes part of the preceding list item as intended:

1. First list

   ```text
   Code block
   ```

2. Still first list

Rationale: Consistent formatting makes it easier to understand a document.

MD030 - Spaces after list markers

Tags: ol, ul, whitespace

Aliases: list-marker-space

Parameters:

  • ol_multi: Spaces for multi-line ordered list items (integer, default 1)
  • ol_single: Spaces for single-line ordered list items (integer, default 1)
  • ul_multi: Spaces for multi-line unordered list items (integer, default 1)
  • ul_single: Spaces for single-line unordered list items (integer, default 1)

Fixable: Some violations can be fixed by tooling

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 https://cirosantilli.com/markdown-style-guide#spaces-after-list-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 the list marker for your selected document style.

Rationale: Violations of this rule can lead to improperly rendered content.

Note: See Prettier.md for compatibility information.

MD031 - Fenced code blocks should be surrounded by blank lines

Tags: blank_lines, code

Aliases: blanks-around-fences

Parameters:

  • list_items: Include list items (boolean, default true)

Fixable: Some violations can be fixed by tooling

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

Set the list_items parameter to false to disable this rule for list items. Disabling this behavior for lists can be useful if it is necessary to create a tight list containing a code fence.

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: blank_lines, bullet, ol, ul

Aliases: blanks-around-lists

Fixable: Some violations can be fixed by tooling

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.

MD033 - Inline HTML

Tags: html

Aliases: no-inline-html

Parameters:

  • allowed_elements: Allowed elements (string[], default [])

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

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

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 into something other than HTML.

MD034 - Bare URL used

Tags: links, url

Aliases: no-bare-urls

Fixable: Some violations can be fixed by tooling

This rule is triggered whenever a URL or email address appears without surrounding angle brackets:

For more info, visit https://www.example.com/ or email [email protected].

To fix this, add angle brackets around the URL or email address:

For more info, visit <https://www.example.com/> or email <[email protected]>.

Note: To include a bare URL or email without it being converted into a link, wrap it in a code span:

Not a clickable link: `https://www.example.com`

Note: The following scenario does not trigger this rule because it could be a shortcut link:

[https://www.example.com]

Note: The following syntax triggers this rule because the nested link could be a shortcut link (which takes precedence):

[text [shortcut] text](https://example.com)

To avoid this, escape both inner brackets:

[link \[text\] link](https://example.com)

Rationale: Without angle brackets, a bare URL or email isn't converted into a link by some Markdown parsers.

MD035 - Horizontal rule style

Tags: hr

Aliases: hr-style

Parameters:

  • style: Horizontal rule style (string, 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.

Rationale: Consistent formatting makes it easier to understand a document.

MD036 - Emphasis used instead of a heading

Tags: emphasis, headers, headings

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

Parameters:

  • punctuation: Punctuation characters (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, or paragraphs ending in punctuation (normal or full-width). Similarly to rule MD026, you can configure what characters are recognized as punctuation.

Rationale: Using emphasis instead of a heading prevents tools from inferring the structure of a document. More information: https://cirosantilli.com/markdown-style-guide#emphasis-vs-headers.

MD037 - Spaces inside emphasis markers

Tags: emphasis, whitespace

Aliases: no-space-in-emphasis

Fixable: Some violations can be fixed by tooling

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 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: code, whitespace

Aliases: no-space-in-code

Fixable: Some violations can be fixed by tooling

This rule is triggered for code span elements that have spaces adjacent to the backticks:

`some text `

` some text`

To fix this, remove any spaces adjacent to the backticks:

`some text`

Note: A single leading and trailing space is allowed by the specification and automatically trimmed (in order to allow for code spans that embed backticks):

`` `backticks` ``

Note: A single leading or trailing space is allowed if used to separate code span markers from an embedded backtick (though the space is not trimmed):

`` ` embedded backtick``

Rationale: Violations of this rule are usually unintentional and may lead to improperly-rendered content. If spaces beside backticks are intentional, this rule can be disabled for that line or file.

MD039 - Spaces inside link text

Tags: links, whitespace

Aliases: no-space-in-links

Fixable: Some violations can be fixed by tooling

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

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

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

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

Rationale: Consistent formatting makes it easier to understand a document.

MD040 - Fenced code blocks should have a language specified

Tags: code, language

Aliases: fenced-code-language

Parameters:

  • allowed_languages: List of languages (string[], default [])
  • language_only: Require language only (boolean, default false)

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
```

To display a code block without syntax highlighting, use:

```text
Plain text in a code block
```

You can configure the allowed_languages parameter to specify a list of languages code blocks could use. Languages are case sensitive. The default value is [] which means any language specifier is valid.

You can prevent extra data from being present in the info string of fenced code blocks. To do so, set the language_only parameter to true.

Info strings with leading/trailing whitespace (ex: js ) or other content (ex: ruby startline=3) will trigger this rule.

Rationale: Specifying a language improves content rendering by using the correct syntax highlighting for code. More information: https://cirosantilli.com/markdown-style-guide#option-code-fenced.

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

Tags: headers, headings

Aliases: first-line-h1, first-line-heading

Parameters:

  • front_matter_title: RegExp for matching title in front matter (string, default ^\s*title\s*[:=])
  • level: Heading level (integer, default 1)

This rule is intended to ensure documents have a title and 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 top-level heading to the beginning of the file:

# File with heading

This is a file with a top-level heading

Because it is common for projects on GitHub to use an image for the heading of README.md and that is not well-supported by Markdown, HTML headings are also permitted by this rule. For example:

<h1 align="center"><img src="https://placekitten.com/300/150"/></h1>

This is a file with a top-level HTML heading

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

If YAML front matter is present and contains a title property (commonly used with blog posts), this rule will not report a violation. To use a different property name in the 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.

Rationale: The top-level heading often acts as the title of a document. More information: https://cirosantilli.com/markdown-style-guide#top-level-header.

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)

Rationale: Empty links do not lead anywhere and therefore don't function as links.

MD043 - Required heading structure

Tags: headers, headings

Aliases: required-headers, required-headings

Parameters:

  • headers: List of headings (string[], default [])
  • headings: List of headings (string[], default [])
  • match_case: Match case of headings (boolean, default false)

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 "zero or more unspecified headings" or 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.

By default, the case of headings in the document is not required to match that of headings. To require that case match exactly, set the match_case parameter to true.

Rationale: Projects may wish to enforce a consistent document structure across a set of similar content.

MD044 - Proper names should have the correct capitalization

Tags: spelling

Aliases: proper-names

Parameters:

  • code_blocks: Include code blocks (boolean, default true)
  • html_elements: Include HTML elements (boolean, default true)
  • names: List of proper names (string[], default [])

Fixable: Some violations can be fixed by tooling

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 and spans. Set the html_elements parameter to false to disable this rule for HTML elements and attributes (such as when using a proper name as part of a path for a/href or img/src).

Rationale: Incorrect capitalization of proper names is usually a mistake.

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 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.

Rationale: Alternate text is important for accessibility and describes the content of an image for people who may not be able to see it.

MD046 - Code block style

Tags: code

Aliases: code-block-style

Parameters:

  • style: Block style (string, default consistent, values consistent / fenced / indented)

This rule is triggered when unwanted or different code block styles are used in the same document.

In the default configuration this rule reports a violation for the following document:

Some text.

    # Indented code

More text.

```ruby
# Fenced code
```

More text.

To fix violations of this rule, use a consistent style (either indenting or code fences).

The specified style can be specific (fenced, indented) or simply require that usage be consistent within the document (consistent).

Rationale: Consistent formatting makes it easier to understand a document.

MD047 - Files should end with a single newline character

Tags: blank_lines

Aliases: single-trailing-newline

Fixable: Some violations can be fixed by tooling

This rule is triggered when there is not a single newline character at the end of a file.

An example that triggers the rule:

# Heading

This file ends without a newline.[EOF]

To fix the violation, add a newline character to the end of the file:

# Heading

This file ends with a newline.
[EOF]

Rationale: Some programs have trouble with files that do not end with a newline.

More information: What's the point in adding a new line to the end of a file?

MD048 - Code fence style

Tags: code

Aliases: code-fence-style

Parameters:

  • style: Code fence style (string, default consistent, values backtick / consistent / tilde)

This rule is triggered when the symbols used in the document for fenced code blocks do not match the configured code fence style:

```ruby
# Fenced code
```

~~~ruby
# Fenced code
~~~

To fix this issue, use the configured code fence style throughout the document:

```ruby
# Fenced code
```

```ruby
# Fenced code
```

The configured list style can be a specific symbol to use (backtick, tilde), or can require that usage be consistent within the document.

Rationale: Consistent formatting makes it easier to understand a document.

MD049 - Emphasis style should be consistent

Tags: emphasis

Aliases: emphasis-style

Parameters:

  • style: Emphasis style should be consistent (string, default consistent, values asterisk / consistent / underscore)

Fixable: Some violations can be fixed by tooling

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

*Text*
_Text_

To fix this issue, use the configured emphasis style throughout the document:

*Text*
*Text*

The configured emphasis style can be a specific symbol to use ("asterisk", "underscore"), or can require that usage be consistent within the document.

Rationale: Consistent formatting makes it easier to understand a document.

MD050 - Strong style should be consistent

Tags: emphasis

Aliases: strong-style

Parameters:

  • style: Strong style should be consistent (string, default consistent, values asterisk / consistent / underscore)

Fixable: Some violations can be fixed by tooling

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

**Text**
__Text__

To fix this issue, use the configured strong style throughout the document:

**Text**
**Text**

The configured strong style can be a specific symbol to use ("asterisk", "underscore"), or can require that usage be consistent within the document.

Rationale: Consistent formatting makes it easier to understand a document.

MD051 - Link fragments should be valid

Tags: links

Aliases: link-fragments

Fixable: Some violations can be fixed by tooling

This rule is triggered when a link fragment does not match any of the fragments that are automatically generated for headings in a document:

# Title

[Link](#fragment)

To fix this issue, change the link fragment to reference an existing heading:

# Title

[Link](#title)

Alternatively, an HTML a tag with an id or a name attribute can be used to define a fragment:

<a id="bookmark"></a>

[Link](#bookmark)

An a tag can be useful in scenarios where a heading is not appropriate or for control over the text of the fragment identifier.

Rationale: GitHub section links are created automatically for every heading when Markdown content is displayed on GitHub. This makes it easy to link directly to different sections within a document. However, section links change if headings are renamed or removed. This rule helps identify broken section links within a document.

Section links are not part of the CommonMark specification. This rule enforces the GitHub heading algorithm which is: convert heading to lowercase, remove punctuation, convert spaces to dashes, append an incrementing integer as needed for uniqueness.

MD052 - Reference links and images should use a label that is defined

Tags: images, links

Aliases: reference-links-images

Links and images in Markdown can provide the link destination or image source at the time of use or can define it elsewhere and use a label for reference. The reference format is convenient for keeping paragraph text clutter-free and makes it easy to reuse the same URL in multiple places.

There are three kinds of reference links and images:

Full: [text][label]
Collapsed: [label][]
Shortcut: [label]

Full: ![text][image]
Collapsed: ![image][]
Shortcut: ![image]

[label]: https://example.com/label
[image]: https://example.com/image

A link or image renders correctly when a corresponding label is defined, but the text displays with brackets if the label is not present. This rule warns of undefined labels for "full" and "collapsed" reference syntax.

"Shortcut" syntax is ambiguous and a missing label will not generate an error. For example, [shortcut] could be a shortcut link or the text "shortcut" in brackets.

MD053 - Link and image reference definitions should be needed

Tags: images, links

Aliases: link-image-reference-definitions

Parameters:

  • ignored_definitions: Ignored definitions (string[], default ["//"])

Fixable: Some violations can be fixed by tooling

Links and images in Markdown can provide the link destination or image source at the time of use or can define it elsewhere and use a label for reference. The reference format is convenient for keeping paragraph text clutter-free and makes it easy to reuse the same URL in multiple places.

Because link and image reference definitions are located separately from where they are used, there are two scenarios where a definition can be unnecessary:

  1. If a label is not referenced by any link or image in a document, that definition is unused and can be deleted.
  2. If a label is defined multiple times in a document, the first definition is used and the others can be deleted.

This rule considers a reference definition to be used if any link or image reference has the corresponding label. The "full", "collapsed", and "shortcut" formats are all supported.

If there are reference definitions that are deliberately unreferenced, they can be ignored by setting the ignored_definitions parameter. The default value of this parameter ignores the following convention for adding non-HTML comments to Markdown:

[//]: # (This behaves like a comment)