The markdownlint-rule-helpers package provides a collection of helper functions used by the internal markdownlint rules. These functions are intended to help developers author custom rules by providing reusable logic and avoiding code duplication.

Warning: These APIs were originally internal and are not officially supported. They may change between releases without notice. Use them at your own discretion.

If a rule performs asynchronous operations (e.g., network requests), set asynchronous: true in the rule definition. The function must return a Promise that resolves when the rule completes.

Warning: Asynchronous rules cannot be used with the synchronous calling context (import { lint } from "markdownlint/sync"); doing so will throw an exception.

MD029 violations occur when ordered lists do not start with '1.' or do not increase in numerical order according to the configured style.

Common Fixes:

• Numerical Order: Ensure numbers increment correctly (e.g., changing 1., 3. to 1., 2.).
• Broken Lists: If a code block or other element is improperly indented between list items, it may 'break' the list into two separate lists. To fix this, indent the code block so it is part of the preceding list item.
• Alignment: The rule supports and preserves 0-prefixing for uniform indentation (e.g., 08., 09., 10.) and right-aligned prefixes (e.g., 8., 9., 10.).

# Improperly indented code block (breaks list):
1. First list

```text
Code block

1. Second list

Fixed (indented code block):

1. First list

   Code block

2. Still first list

To use markdownlint in a web browser, first generate the necessary scripts using the build command, then include the minified browser script in your HTML. The library is exposed via globalThis.markdownlint.

```bash
# Generate scripts
npm run build-demo

<!-- In your HTML --> <script src="demo/markdownlint-browser.min.js"></script>

<script> const options = { "strings": { "content": "Some Markdown to lint." } };

// Access via globalThis const results = globalThis.markdownlint.lintSync(options); </script>

You can change the configuration of specific rules for an entire file using the markdownlint-configure-file comment. The content following the comment must be a JSON object. Multiple comments are applied in top-to-bottom order.

By default, the content is parsed as JSON, but you can use options.configParsers in the API to support other formats.

<!-- markdownlint-configure-file {"hr-style": {"style": "---"}} -->

<!-- markdownlint-configure-file
{
  "hr-style": {
    "style": "---"
  },
  "no-trailing-spaces": false
}
-->

You can temporarily change the linting state and then revert to the previous configuration using capture comments.

Because the initial configuration is captured by default, you can simply use <!-- markdownlint-disable --> followed by <!-- markdownlint-restore --> to wrap a section where you want to ignore all rules and then return to the document's original settings.

<!-- markdownlint-disable -->
any violations you want
<!-- markdownlint-restore -->

If you encounter an MD024 error, it means you have headings with identical text.

Example of violation:

# Some text

## Some text

How to fix: Ensure each heading has unique text content:

# Some text

## Some more text

Using siblings_only to allow duplicates: If you are writing a changelog where duplicate headings are expected under different parent headings, set the siblings_only parameter to true in your configuration:

# Change log

## 1.0.0

### Features

## 2.0.0

### Features

The MD037 rule (alias: no-space-in-emphasis) triggers when there are spaces between emphasis markers (bold/italic) and the text they enclose.

Incorrect: ** bold ** or _ italic _

Correct: **bold** or _italic_