# 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: ```markdown # 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: ```markdown # 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: . ## ~~`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](md041.md) 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: ```markdown ## This isn't an H1 heading ### Another heading ``` The first heading in the document should be an h1 heading: ```markdown # 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: . ## `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: ```markdown # ATX style H1 ## Closed ATX style H2 ## Setext style H1 =============== ``` To fix the issue, use consistent heading styles throughout the document: ```markdown # 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): ```markdown 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: ```markdown 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: Most 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: ```markdown * Item 1 + Item 2 - Item 3 ``` To fix this issue, use the configured style for list items throughout the document: ```markdown * 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: ```markdown * 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: Most 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: ```markdown * 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: ```markdown * 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: ```markdown ... 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: ```markdown ... 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: Most violations can be fixed by tooling This rule is triggered when top-level lists don't start at the beginning of a line: ```markdown Some text * List item * List item ``` To fix, ensure that top-level list items are not indented: ```markdown 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. ```markdown 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: Most 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: ```markdown * List item * Nested list item indented by 3 spaces ``` Corrected Example: ```markdown * 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][markdown-style-guide] and [Marked app\ support][marked-app-support]. Note: See [Prettier.md](Prettier.md) for compatibility information. [markdown-style-guide]: https://cirosantilli.com/markdown-style-guide#indentation-of-content-inside-lists [marked-app-support]: http://support.markedapp.com/discussions/problems/21-sub-lists-not-indenting ## `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: Most 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 (\
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`. ```markdown 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`): ```markdown - 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: Most 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: ```markdown Some text * hard tab character used to indent the list item ``` Corrected example: ```markdown 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: Most 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): ```markdown (Incorrect link syntax)[https://www.example.com/] ``` To fix this, swap the `[]` and `()` around: ```markdown [Correct link syntax](https://www.example.com/) ``` Note: [Markdown Extra](https://en.wikipedia.org/wiki/Markdown_Extra)-style footnotes do not trigger this rule: ```markdown 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: Most violations can be fixed by tooling This rule is triggered when there are multiple consecutive blank lines in the document: ```markdown Some text here Some more text here ``` To fix this, delete the offending lines: ```markdown 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): ```markdown 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: . ## `MD014` - Dollar signs used before commands without showing output Tags: `code` Aliases: `commands-show-output` Fixable: Most 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 ($): ```markdown $ ls $ cat foo $ less bar ``` The dollar signs are unnecessary in this situation, and should not be included: ```markdown ls cat foo less bar ``` Showing output for commands preceded by dollar signs does not trigger this rule: ```markdown $ 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: ```markdown $ 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 for more information. ## `MD018` - No space after hash on atx style heading Tags: `atx`, `headers`, `headings`, `spaces` Aliases: `no-missing-space-atx` Fixable: Most violations can be fixed by tooling This rule is triggered when spaces are missing after the hash characters in an atx style heading: ```markdown #Heading 1 ##Heading 2 ``` To fix this, separate the heading text from the hash character by a single space: ```markdown # 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: Most 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: ```markdown # Heading 1 ## Heading 2 ``` To fix this, separate the heading text from the hash character by a single space: ```markdown # 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: Most violations can be fixed by tooling This rule is triggered when spaces are missing inside the hash characters in a closed atx style heading: ```markdown #Heading 1# ##Heading 2## ``` To fix this, separate the heading text from the hash character by a single space: ```markdown # 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: Most 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: ```markdown # Heading 1 # ## Heading 2 ## ``` To fix this, separate the heading text from the hash character by a single space: ```markdown # 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: Most 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: ```markdown # 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): ```markdown # 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](md012.md) 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: Most violations can be fixed by tooling This rule is triggered when a heading is indented by one or more spaces: ```markdown Some text # Indented heading ``` To fix this, ensure that all headings start at the beginning of the line: ```markdown 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: ```markdown # Some text ## Some text ``` To fix this, ensure that the content of each heading is different: ```markdown # 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): ```markdown # 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: ```markdown # 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.): ```markdown # 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](https://en.wikipedia.org/wiki/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: Most 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: ```markdown # This is a heading. ``` To fix this, remove the trailing punctuation: ```markdown # 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][html-entity-references] like `©`, `©`, and `©` is ignored by this rule. Rationale: Headings are not meant to be full sentences. More information: [Punctuation at the end of headers][end-punctuation]. [end-punctuation]: https://cirosantilli.com/markdown-style-guide#punctuation-at-the-end-of-headers [html-entity-references]: https://en.wikipedia.org/wiki/List_of_XML_and_HTML_character_entity_references ## `MD027` - Multiple spaces after blockquote symbol Tags: `blockquote`, `indentation`, `whitespace` Aliases: `no-multiple-space-blockquote` Fixable: Most violations can be fixed by tooling This rule is triggered when blockquotes have more than one space after the blockquote (`>`) symbol: ```markdown > This is a blockquote with bad indentation > there should only be one. ``` To fix, remove any extraneous space: ```markdown > 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: ```markdown > 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: ```markdown > 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: ```markdown > 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': ```markdown 1. Do this. 1. Do that. 1. Done. ``` Examples of valid lists if the style is configured as 'ordered': ```markdown 1. Do this. 2. Do that. 3. Done. ``` ```markdown 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': ```markdown 0. Do this. 0. Do that. 0. Done. ``` Example invalid list for all styles: ```markdown 1. Do this. 3. Done. ``` This rule supports 0-prefixing ordered list items for uniform indentation: ```markdown ... 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: ~~~markdown 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: ~~~markdown 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: Most 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: ```markdown * 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 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: ```markdown * Foo * Bar * Baz ``` vs. ```markdown * Foo Second paragraph * Bar ``` or ```markdown 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](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: Most 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: ````markdown 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): ````markdown 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](https://spec.commonmark.org/0.29/#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: Most 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: ```markdown 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): ```markdown 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: ```markdown

Inline HTML heading

``` To fix this, use 'pure' Markdown instead of including raw HTML: ```markdown # 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: Most violations can be fixed by tooling This rule is triggered whenever a URL is given that isn't surrounded by angle brackets: ```markdown For more information, see https://www.example.com/. ``` To fix this, add angle brackets around the URL: ```markdown For more information, see . ``` Note: To use 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: ```markdown `https://www.example.com` ``` Note: The following scenario does *not* trigger this rule to avoid conflicts with `MD011`/`no-reversed-links`: ```markdown [https://www.example.com] ``` The use of quotes around a bare link will *not* trigger this rule, either: ```markdown "https://www.example.com" 'https://www.example.com' ``` Rationale: Without angle brackets, the URL isn't converted into a link by many 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: ```markdown --- - - - *** * * * **** ``` To fix this, ensure any horizontal rules used in the document are consistent, or match the given style if the rule is so configured: ```markdown --- --- ``` 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: ```markdown **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: ```markdown # 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: . ## `MD037` - Spaces inside emphasis markers Tags: `emphasis`, `whitespace` Aliases: `no-space-in-emphasis` Fixable: Most 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: ```markdown 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: ```markdown 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: Most violations can be fixed by tooling This rule is triggered for code span elements that have spaces adjacent to the backticks: ```markdown `some text ` ` some text` ``` To fix this, remove any spaces adjacent to the backticks: ```markdown `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): ```markdown `` `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): ```markdown `` ` 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: Most violations can be fixed by tooling This rule is triggered on links that have spaces surrounding the link text: ```markdown [ a link ](https://www.example.com/) ``` To fix this, remove the spaces surrounding the link text: ```markdown [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: ````markdown ``` #!/bin/bash echo Hello world ``` ```` To fix this, add a language specifier to the code block: ````markdown ```bash #!/bin/bash echo Hello world ``` ```` To display a code block without syntax highlighting, use: ````markdown ```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: . ## `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: ```markdown This is a file without a heading ``` To fix this, add a top-level heading to the beginning of the file: ```markdown # 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: ```markdown

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](https://en.wikipedia.org/wiki/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: . ## `MD042` - No empty links Tags: `links` Aliases: `no-empty-links` This rule is triggered when an empty link is encountered: ```markdown [an empty link]() ``` To fix the violation, provide a destination for the link: ```markdown [a valid link](https://example.com/) ``` Empty fragments will trigger this rule: ```markdown [an empty fragment](#) ``` But non-empty fragments will not: ```markdown [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: ```markdown # Head ## Item ### Detail ``` Set the `headings` parameter to: ```json [ "# Head", "## Item", "### Detail" ] ``` To allow optional headings as with the following structure: ```markdown # 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: ```json [ "# 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: Most 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: ```json [ "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: ```markdown ![Alternate text](image.jpg) ``` Or with reference syntax as: ```markdown ![Alternate text][ref] ... [ref]: image.jpg "Optional title" ``` Guidance for writing alternate text is available from the [W3C][w3c], [Wikipedia][wikipedia], and [other locations][phase2technology]. Rationale: Alternate text is important for accessibility and describes the content of an image for people who may not be able to see it. [phase2technology]: https://www.phase2technology.com/blog/no-more-excuses [w3c]: https://www.w3.org/WAI/alt/ [wikipedia]: https://en.wikipedia.org/wiki/Alt_attribute ## `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: Most 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: ```markdown # Heading This file ends without a newline.[EOF] ``` To fix the violation, add a newline character to the end of the file: ```markdown # 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?][stack-exchange] [stack-exchange]: https://unix.stackexchange.com/questions/18743/whats-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: ````markdown ```ruby # Fenced code ``` ~~~ruby # Fenced code ~~~ ```` To fix this issue, use the configured code fence style throughout the document: ````markdown ```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: Most 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: ```markdown *Text* _Text_ ``` To fix this issue, use the configured emphasis style throughout the document: ```markdown *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: Most 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: ```markdown **Text** __Text__ ``` To fix this issue, use the configured strong style throughout the document: ```markdown **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` This rule is triggered when a link fragment does not match any of the fragments that are automatically generated for headings in a document: ```markdown # Title [Link](#fragment) ``` To fix this issue, change the link fragment to reference an existing heading: ```markdown # Title [Link](#title) ``` Alternatively, an HTML `a` tag with an `id` or a `name` attribute can be used to define a fragment: ```markdown [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][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][github-heading-algorithm] which is: convert heading to lowercase, remove punctuation, convert spaces to dashes, append an incrementing integer as needed for uniqueness. [github-section-links]: https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#section-links [github-heading-algorithm]: https://github.com/gjtorikian/html-pipeline/blob/main/lib/html/pipeline/toc_filter.rb ## `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: ```markdown 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: Most 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: ```markdown [//]: # (This behaves like a comment) ```