remark-lint is a markdown code style linter. Another linter? Yes. 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 this one).

• Installation
• Command line
• Programmatic
• Rules
• Configuring remark-lint
• Using remark to fix your markdown
• Integrations
• List of Presets
• List of External Rules
• Related
• Contribute
• License

npm:

npm install remark-lint

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

npm install --save 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).

Use remark-lint together with remark:

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

Let’s say example.js looks as follows:

var report = require('vfile-reporter');
var remark = require('remark');
var styleGuide = require('remark-preset-lint-markdown-style-guide');

var file = remark().use(styleGuide).processSync('_Hello world_');

console.log(report(file));

Now, running node example.js yields:

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

⚠ 1 warning

doc/rules.md lists all available official rules.

remark-lint is a remark plug-in 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 it 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

⚠ 2 warnings

In addition, 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 re-enabled):

# 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!

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, table fences are aligned, and more.

If you require('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:

var report = require('vfile-reporter');
var remark = require('remark');
var emphasisMarker = require('remark-lint-emphasis-marker');
var strongMarker = require('remark-lint-strong-marker');

remark()
  .use(emphasisMarker, '*')
  .use(strongMarker, '*')
  // ^ two `remark-lint` rules.
  .use({
    settings: {emphasis: '*', strong: '*'}
    // ^ `remark-stringify` settings.
  })
  .process('_Hello_, __world__!', function (err, file) {
    console.error(report(err || 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**!

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

var report = require('vfile-reporter');
var unified = require('unified');
var parse = require('remark-parse');
var stringify = require('remark-stringify');
var emphasisMarker = require('remark-lint-emphasis-marker');
var strongMarker = require('remark-lint-strong-marker');

unified()
  .use(parse)
  .use(emphasisMarker, '*')
  .use(strongMarker, '*')
  // ^ two `remark-lint` rules.
  .use(stringify, {emphasis: '*', strong: '*'})
  // ^ `remark-stringify` with settings.
  .process('_Hello_, __world__!', function (err, file) {
    console.error(report(err || file));
    console.log(String(file));
  });

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

• linter-markdown (Atom) — use remark-lint from Atom
• linter-remark (Atom) — use all of remark from Atom
• 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

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

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 syntaxes that do not work correctly across vendors

External rules can be loaded just like normal rules.

⚠️ means the rule has not been updated for remark-lint 6.0.0.

• 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-no-dead-urls — Check that external links are alive
• 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 headings parsing is not broken by accidental irregular whitespaces
• remark-lint-no-leading-spaces — ⚠️ Warn about leading white-space
• remark-lint-list-item-punctuation — ⚠️ check if list items end in periods
• remark-lint-are-links-valid — Check if your links are reachable and/or unique
• remark-lint-sentence-newline — ⚠️ Ensure sentences are followed by a newline
• remark-lint-no-trailing-spaces — ⚠️ Warn about trailing white-space
• 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-validate-links — Validate if links point to existing headings and files in markdown

See contributing.md in remarkjs/remark for ways to get started.

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MIT © Titus Wormer