markdownlint/README.md

# markdownlint

> A Node.js style checker and lint tool for Markdown files.

## Install

```shell
npm install markdownlint --save-dev
```

## Overview

The [Markdown](http://en.wikipedia.org/wiki/Markdown) markup language is
designed to be easy to read, write, and understand. It succeeds - and its
flexibility is both a benefit and a drawback. Many styles are possible, so
formatting can be inconsistent. Some constructs don't work well in all
parsers and should be avoided.

`markdownlint` is a [static analysis](http://en.wikipedia.org/wiki/Static_program_analysis)
tool for [Node.js](https://nodejs.org/) and [io.js](https://iojs.org/) with a
library of rules to enforce standards and consistency for Markdown files. It
was inspired by - and heavily influenced by - Mark Harrison's
[markdownlint](https://github.com/mivok/markdownlint) for
[Ruby](https://www.ruby-lang.org/). The rules, rule documentation, and test
cases come directly from that project.

> If you need a Ruby implementation or a [CLI](http://en.wikipedia.org/wiki/Command-line_interface),
> please consider the [mdl](https://rubygems.org/gems/mdl) gem.

## Rules

* MD001 - Header levels should only increment by one level at a time
* MD002 - First header should be a h1 header
* MD003 - Header style
* MD004 - Unordered list style
* MD005 - Inconsistent indentation for list items at the same level
* MD006 - Consider starting bulleted lists at the beginning of the line
* MD007 - Unordered list indentation
* MD009 - Trailing spaces
* MD010 - Hard tabs
* MD011 - Reversed link syntax
* MD012 - Multiple consecutive blank lines
* MD013 - Line length
* MD014 - Dollar signs used before commands without showing output
* MD018 - No space after hash on atx style header
* MD019 - Multiple spaces after hash on atx style header
* MD020 - No space inside hashes on closed atx style header
* MD021 - Multiple spaces inside hashes on closed atx style header
* MD022 - Headers should be surrounded by blank lines
* MD023 - Headers must start at the beginning of the line
* MD024 - Multiple headers with the same content
* MD025 - Multiple top level headers in the same document
* MD026 - Trailing punctuation in header
* MD027 - Multiple spaces after blockquote symbol
* MD028 - Blank line inside blockquote
* MD029 - Ordered list item prefix
* MD030 - Spaces after list markers
* MD031 - Fenced code blocks should be surrounded by blank lines
* MD032 - Lists should be surrounded by blank lines

See [Rules.md](doc/Rules.md) for more details.

## API

```js
/**
 * Lint specified Markdown files according to configurable rules.
 *
 * @param {Object} options Configuration options.
 * @param {Function} callback Callback (err, result) function.
 * @returns {void}
 */
function markdownlint(options, callback) { ... }
```

### options

Type: `Object`

Configures the function.

#### options.files

Type: `Array` of `String`

List of files to lint.

Each array element should be a single file (via relative or absolute path);
[globbing](http://en.wikipedia.org/wiki/Glob_%28programming%29) is the caller's
responsibility.

Example: `[ "one.md", "dir/two.md" ]`

#### options.config

Type: `Object` mapping `String` to `Object | Boolean`

Configures the rules to use.

Object keys are rule names and values are the rule's configuration.
The value `false` disables a rule, `true` enables its default configuration,
and passing an object customizes its settings. Setting the special `default`
rule to `true` or `false` includes/excludes all rules by default.

Example:

```json
{
  "default": true,
  "MD007": {
    "indent": 4
  },
  "MD013": {
    "line_length": 100
  },
  "MD029": false
}
```

### callback

Type: `Function` taking (`Error`, `Object`)

Function to call upon completion.

See below for an example of the structure of the `result` object.

## Usage

Invoke `markdownlint` and use the `result` object's `toString` method:

```js
var markdownlint = require("markdownlint");

var options = {
  "files": [ "good.md", "bad.md" ]
};

markdownlint(options, function callback(err, result) {
  if (!err) {
    console.log(result.toString());
  }
});
```

Outputs:

```text
bad.md: 3: MD010 Hard tabs
bad.md: 1: MD018 No space after hash on atx style header
bad.md: 3: MD018 No space after hash on atx style header
```

Or examine the `result` object directly:

```js
markdownlint(options, function callback(err, result) {
  if (!err) {
    console.dir(result, { "colors": true });
  }
});
```

Outputs:

```json
{
  'good.md': {},
  'bad.md': {
    MD010: [ 3 ],
    MD018: [ 1, 3 ]
  }
}
```

Integration with the [gulp](http://gulpjs.com/) build system is straightforward:

```js
var gulp = require("gulp");
var through2 = require("through2");
var markdownlint = require("markdownlint");

gulp.task("markdownlint", function task() {
  return gulp.src("*.md", { "read": false })
    .pipe(through2.obj(function obj(file, enc, next) {
      markdownlint(
        { "files": [ file.relative ] },
        function callback(err, result) {
          var resultString = (result || "").toString();
          if (resultString) {
            console.log(resultString);
          }
          next(err, file);
        });
    }));
});
```

Outputs:

```text
[00:00:00] Starting 'markdownlint'...
bad.md: 3: MD010 Hard tabs
bad.md: 1: MD018 No space after hash on atx style header
bad.md: 3: MD018 No space after hash on atx style header
[00:00:00] Finished 'markdownlint' after 10 ms
```

Integration with the [Grunt](http://gruntjs.com/) build system is similar:

```js
var markdownlint = require("markdownlint");

module.exports = function wrapper(grunt) {
  grunt.initConfig({
    "markdownlint": {
      "example": {
        "src": [ "*.md" ]
      }
    }
  });

  grunt.registerMultiTask("markdownlint", function task() {
    var done = this.async();
    markdownlint(
      { "files": this.filesSrc },
      function callback(err, result) {
        var resultString = err || ((result || "").toString());
        if (resultString) {
          grunt.fail.warn("\n" + resultString + "\n");
        }
        done(!err || !resultString);
      });
  });
};
```

Outputs:

```text
Running "markdownlint:example" (markdownlint) task
Warning:
bad.md: 3: MD010 Hard tabs
bad.md: 1: MD018 No space after hash on atx style header
bad.md: 3: MD018 No space after hash on atx style header
 Use --force to continue.
```

## Release History

* 0.0.1 - Initial release.