remark plugins to lint Markdown.

Ensuring the Markdown you (and contributors) write is of great quality will provide better rendering in all the different markdown parsers, and makes sure less refactoring is needed afterwards.

What is quality? That’s up to you, but there are sensible presets.

remark-lint is built on remark, a powerful Markdown processor powered by plugins (such as these).

Contents

• Install
• CLI
• API
• Configuring remark-lint
• Using remark to fix your Markdown
• Integrations
• Rules
• List of presets
• List of external rules
• Create a custom rule
• Security
• Related
• Contribute
• License

Install

This package is ESM only: Node 12+ is needed to use it and it must be imported instead of required.

npm:

npm install remark-lint

CLI

Use remark-lint with remark-cli through a preset.

npm install --save-dev remark-cli remark-preset-lint-recommended

Then, configure remark in your package.json:

  // …
  "scripts": {
    "lint-md": "remark ."
  },
  // …
  "remarkConfig": {
    "plugins": ["remark-preset-lint-recommended"]
  }
  // …

Let’s say there’s an example.md that looks as follows:

* Hello

[World][]

Now, running our lint-md script with npm run lint-md yields:

example.md
       1:3  warning  Incorrect list-item indent: add 2 spaces  list-item-indent
  3:1-3:10  warning  Found reference to undefined definition   no-undefined-references
⚠ 2 warnings

See doc/rules.md for what those warnings are (and how to turn them off).

API

Use remark-lint together with remark:

npm install remark remark-preset-lint-markdown-style-guide

Let’s say example.js looks as follows:

import {remark} from 'remark'
import {reporter} from 'vfile-reporter'
import remarkPresetLintMarkdownStyleGuide from 'remark-preset-lint-markdown-style-guide'

const file = remark()
  .use(remarkPresetLintMarkdownStyleGuide)
  .processSync('_Hello world_')

console.log(reporter(file))

Now, running node example.js yields:

  1:1-1:14  warning  Emphasis should use `*` as a marker  emphasis-marker  remark-lint

⚠ 1 warning

Configuring remark-lint

remark-lint is a remark plugin and when used on the CLI supports configuration through its configuration files.

An example .remarkrc file could look as follows:

{
  "plugins": [
    "remark-preset-lint-recommended",
    ["remark-lint-list-item-indent", false]
  ]
}

The preset turns on remark-lint-list-item-indent, but setting a plugin to false later turns it off again.

Using our example.md from before:

* Hello

[World][]

Now, running npm run lint-md yields:

example.md
   3:1-3:10  warning  Found reference to undefined definition   no-undefined-references  remark-lint

⚠ 2 warnings

You can also provide configuration comments to turn a rule on or off inside a file. Note that you cannot change a setting, such as maximum-line-length, just whether messages are shown or not. Read more about configuration comments in remark-message-controls documentation.

The following file will warn twice for the duplicate headings:

# Hello

## Hello

### Hello

The following file will warn once (the second heading is ignored, but the third is enabled again):

# Hello

<!--lint disable no-duplicate-headings-->

## Hello

<!--lint enable no-duplicate-headings-->

### Hello

Note

: You’ll need the blank lines between comments and other nodes!

Using remark to fix your Markdown

remark-stringify can format markdown syntax. It ensures a single style is used: list items use one type of bullet (*, -, +), emphasis (* or _) and importance (__ or **) use a standard marker, and more.

Example

If you import('remark'), remark-stringify is included unless an output format other than markdown (such as HTML) is defined.

Say we have the following file, example.js, showing how formatting rules can be used:

import {reporter} from 'vfile-reporter'
import {remark} from 'remark'
import remarkLintEmphasisMarker from 'remark-lint-emphasis-marker'
import remarkLintStrongMarker from 'remark-lint-strong-marker'

remark()
  .use(remarkLintEmphasisMarker, '*')
  .use(remarkLintStrongMarker, '*')
  // ^ two `remark-lint` rules.
  .use({
    settings: {emphasis: '*', strong: '*'}
    // ^ `remark-stringify` settings.
  })
  .process('_Hello_, __world__!')
  .then((file) => {
    console.error(reporter(file))
    console.log(String(file))
  })

Now, running node example yields warnings and a formatted file:

    1:1-1:8  warning  Emphasis should use `*` as a marker  emphasis-marker  remark-lint
  1:10-1:19  warning  Strong should use `*` as a marker    strong-marker    remark-lint

⚠ 2 warnings
*Hello*, **world**!

Example

If you’re using remark-stringify explicitly, you can pass options like any other plugin, like so:

import {reporter} from 'vfile-reporter'
import {unified} from 'unified'
import remarkParse from 'remark-parse'
import remarkStringify from 'remark-stringify'
import remarkLintEmphasisMarker from 'remark-lint-emphasis-marker'
import remarkLintStrongMarker from 'remark-lint-strong-marker'

unified()
  .use(remarkParse)
  .use(remarkLintEmphasisMarker, '*')
  .use(remarkLintStrongMarker, '*')
  // ^ two `remark-lint` rules.
  .use(remarkStringify, {emphasis: '*', strong: '*'})
  // ^ `remark-stringify` with settings.
  .process('_Hello_, __world__!')
  .then((file) => {
    console.error(reporter(file))
    console.log(String(file))
  })

Now, when running node example, this results in the same output as the previous example.

Example

If you’re using remark-cli, remark-stringify is included unless an output format other than markdown (such as HTML) is defined. In this case you can configure remark-stringify settings using the -s, --settings flag or a "settings" field in remark configuration files.

Say we have the following file, example.md:

_Hello_, __world__!

And our package.json looks as follows:

  // …
  "remarkConfig": {
    "settings": {
      "emphasis": "*",
      "strong": "*"
    },
    "plugins": [
      "remark-lint-emphasis-marker",
      "remark-lint-strong-marker"
    ]
  }
  // …

Now, running remark example.md yields warnings and a formatted file:

*Hello*, **world**!
example.md
    1:1-1:8  warning  Emphasis should use `*` as a marker  emphasis-marker  remark-lint
  1:10-1:19  warning  Strong should use `*` as a marker    strong-marker    remark-lint

⚠ 2 warnings

Note: running remark example.md -o or remark example.md --output overwrites example.md and formats it. So, if you’d run that twice (the first pass lints and fixes the Markdown, the second pass checks it again), you’d see the output example.md: written as all warnings are now fixed.

Integrations

• linter-remark (Atom) — use all of remark from Atom
• vscode-remark-lint (VS Code) — use remark-lint from Visual Studio Code
• SublimeLinter-contrib-remark-lint (Sublime) — use remark-lint from Sublime Text
• ale (Vim) — use remark-lint from Vim
• gulp-remark (Gulp) — use all of remark with Gulp
• grunt-remark (Grunt) — use all of remark with Grunt
• jest-runner-remark (Jest) — use all of remark with Jest

We’re interested in more integrations. Let us know if we can help.

Rules

doc/rules.md lists all available official rules.

List of presets

Presets can be loaded just like other plugins.

• remark-preset-lint-consistent — rules that enforce consistency
• remark-preset-lint-markdown-style-guide — rules that enforce the markdown style guide
• remark-preset-lint-recommended — rules that prevent mistakes or stuff that fails across vendors.

List of external rules

External rules can be loaded just like normal rules.

• remark-lint-alphabetize-lists — Ensure list items are in alphabetical order
• remark-lint-appropriate-heading — Check that the top level heading matches the directory name
• remark-lint-blank-lines-1-0-2 — Ensure a specific number of lines between blocks
• remark-lint-books-links — Ensure links in lists of books follow a standard format
• remark-lint-code — Lint fenced code blocks by corresponding language tags, currently supporting ESLint
• remark-lint-match-punctuation — Ensures punctuations are used in pairs if necessary.
• remark-lint-mdash-style — Ensure em-dash (—) style follows a standard format
• remark-lint-no-chinese-punctuation-in-number — Ensures that Chinese punctuation’s not used in numbers
• remark-lint-no-dead-urls — Check that external links are alive
• remark-lint-no-long-code — Ensures that each line in code block won't be too long.
• remark-lint-no-repeat-punctuation — Ensures punctuation is not repeated
• remark-lint-emoji-limit — Enforce a limit of emoji per paragraph
• remark-lint-no-empty-sections — Ensure every heading is followed by content (forming a section)
• remark-lint-heading-length — Ensure headings have the appropriate length
• remark-lint-heading-whitespace — Ensure heading parsing is not broken by weird whitespace
• remark-lint-are-links-valid — Check if your links are reachable and/or unique
• remark-lint-spaces-around-number — Ensures there are spaces around number and Chinese.
• remark-lint-spaces-around-word — Ensures there are spaces around English word and Chinese.
• remark-lint-no-url-trailing-slash — Ensure that the href of links has no trailing slash
• remark-lint-write-good — Wrapper for write-good
• remark-lint-double-link — Ensure the same URL is not linked multiple times.

Create a custom rule

Follow this comprehensive tutorial on how to create your own custom rule for remark.

Security

Use of remark-lint does not mutate the tree so there are no openings for cross-site scripting (XSS) attacks. Messages from linting rules may be hidden from user content though, causing builds to fail or pass, or changing a report.

Related

• remark-validate-links — Validate if links point to existing headings and files in markdown

Contribute

See contributing.md in remarkjs/.github for ways to get started. See support.md for ways to get help.

This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.

License

MIT © Titus Wormer