mdast-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 the defaults are sensible 👌.

mdast-lint has lots of tests. Supports Node, io.js, and the browser. 100% coverage. 40+ rules. It’s build on mdast, a powerful markdown processor powered by plugins (such as this one).

Table of Contents

• Installation
• Command line
• Programmatic
• Rules
• Configuring mdast-lint
• Combining with other plug-ins
• Using mdast to fix your markdown
• License

Installation

npm:

npm install mdast-lint

mdast-lint is also available for bower, component, duo, and for AMD, CommonJS, and globals.

Command line

Use mdast-lint together with mdast:

npm install --global mdast mdast-lint

Let’s say example.md looks as follows:

* Hello

-   World

Then, to run mdast-lint on example.md:

mdast -u mdast-lint example.md
#
# Yields:
#
# example.md
#   1:3  warning  Incorrect list-item content indent: add 2 spaces  list-item-indent
#   3:1  warning  Invalid ordered list item marker: should be `*`   unordered-list-marker-style
#
# ✖ 2 problems (0 errors, 2 warnings)
#
# *   Hello
#
#
# *   World
#

See doc/rules.md to see what those warnings are, and how to turn them off.

Programmatic

doc/api.md describes how to use mdast-lint’s programatic interface in JavaScript.

Rules

doc/rules.md describes all available rules, what they check for, examples of markdown they warn for, and how to fix their warnings.

Configuring mdast-lint

mdast-lint is just an mdast plug-in. Meaning, you can opt to configure using configuration files. Read more about these files (.mdastrc or package.json) in mdast’s docs.

An example .mdastrc file could look as follows:

{
  "plugins": {
    "lint": {
        "no-multiple-toplevel-headings": false,
        "maximum-line-length": 79,
        "emphasis-marker": "_",
        "strong-marker": "*"
    }
  },
  "settings": {
    "commonmark": true
  }
}

Where the object at plugins.lint is a map of ruleIds and their values. The object at settings determines how mdast parses (and compiles) markdown code. Read more about the latter on mdast’s readme.

In addition, you can also provide configuration comments to turn a rule on or off inside a file (note that you cannot change what a setting, such as maximum-line-length, you’re either enabling or disabling warnings).

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

Combining with other plug-ins

As noted above, mdast-lint is just an mdast plugin. Meaning, you can use other plug-ins together with it. Such as mdast-toc, which will generate a table of contents for you.

However, these plug-ins will generate new nodes in the syntax tree, nodes which previously weren’t available: thus, they have no positional information, and mdast-lint cannot warn you about them.

Therefore, you need to do two things:

• Process the files twice (this is similar to how LaTeX works);
• Ensure mdast-lint runs before the plug-in’s which generate content.

Using mdast to fix your markdown

One of mdast’s cool parts is that it compiles to very clean, and highly cross-vendor supported markdown. It’ll ensure list items use a single bullet, emphasis and strong use a standard marker, and that your table fences are aligned.

mdast should be able to fix most of your styling issues automatically, and I strongly suggest checking out how it can make your life easier 👍

License

MIT © Titus Wormer