Markdown Abstract Syntax Tree.

mdast is a specification for representing markdown in a syntax tree. It implements unist. It can represent several flavours of markdown, such as CommonMark and GitHub Flavored Markdown.

This document may not be released. See releases for released documents. The latest released version is 4.0.0.

• Introduction
  • Where this specification fits
• Types
• Nodes (abstract)
  • Literal
  • Parent
• Nodes
  • Blockquote
  • Break
  • Code
  • Definition
  • Emphasis
  • Heading
  • HTML
  • Image
  • ImageReference
  • InlineCode
  • Link
  • LinkReference
  • List
  • ListItem
  • Paragraph
  • Root
  • Strong
  • Text
  • ThematicBreak
• Mixin
  • Alternative
  • Association
  • Reference
  • Resource
• Enumeration
  • referenceType
• Content model
  • Content
  • FlowContent
  • ListContent
  • PhrasingContent
• Extensions
  • GFM
  • Frontmatter
  • Footnotes
  • MDX
• Glossary
• List of utilities
• References
• Security
• Related
• Contribute
• Acknowledgments
• License

This document defines a format for representing markdown as an abstract syntax tree. Development of mdast started in July 2014, in remark, before unist existed. This specification is written in a Web IDL-like grammar.

mdast extends unist, a format for syntax trees, to benefit from its ecosystem of utilities.

mdast relates to JavaScript in that it has a rich ecosystem of utilities for working with compliant syntax trees in JavaScript. However, mdast is not limited to JavaScript and can be used in other programming languages.

mdast relates to the unified and remark projects in that mdast syntax trees are used throughout their ecosystems.

If you are using TypeScript, you can use the unist types by installing them with npm:

npm install @types/mdast

interface Literal <: UnistLiteral {
  value: string
}

Literal (UnistLiteral) represents an abstract interface in mdast containing a value.

Its value field is a string.

interface Parent <: UnistParent {
  children: [MdastContent]
}

Parent (UnistParent) represents an abstract interface in mdast containing other nodes (said to be children).

Its content is limited to only other mdast content.

interface Blockquote <: Parent {
  type: 'blockquote'
  children: [FlowContent]
}

Blockquote (Parent) represents a section quoted from somewhere else.

Blockquote can be used where flow content is expected. Its content model is also flow content.

For example, the following markdown:

> Alpha bravo charlie.

Yields:

{
  type: 'blockquote',
  children: [{
    type: 'paragraph',
    children: [{type: 'text', value: 'Alpha bravo charlie.'}]
  }]
}

interface Break <: Node {
  type: 'break'
}

Break (Node) represents a line break, such as in poems or addresses.

Break can be used where phrasing content is expected. It has no content model.

For example, the following markdown:

foo··
bar

Yields:

{
  type: 'paragraph',
  children: [
    {type: 'text', value: 'foo'},
    {type: 'break'},
    {type: 'text', value: 'bar'}
  ]
}

interface Code <: Literal {
  type: 'code'
  lang: string?
  meta: string?
}

Code (Literal) represents a block of preformatted text, such as ASCII art or computer code.

Code can be used where flow content is expected. Its content is represented by its value field.

This node relates to the phrasing content concept InlineCode.

A lang field can be present. It represents the language of computer code being marked up.

If the lang field is present, a meta field can be present. It represents custom information relating to the node.

For example, the following markdown:

    foo()

Yields:

{
  type: 'code',
  lang: null,
  meta: null,
  value: 'foo()'
}

And the following markdown:

```js highlight-line="2"
foo()
bar()
baz()
```

Yields:

{
  type: 'code',
  lang: 'javascript',
  meta: 'highlight-line="2"',
  value: 'foo()\nbar()\nbaz()'
}

interface Definition <: Node {
  type: 'definition'
}

Definition includes Association
Definition includes Resource

Definition (Node) represents a resource.

Definition can be used where content is expected. It has no content model.

Definition includes the mixins Association and Resource.

Definition should be associated with LinkReferences and ImageReferences.

For example, the following markdown:

[Alpha]: https://example.com

Yields:

{
  type: 'definition',
  identifier: 'alpha',
  label: 'Alpha',
  url: 'https://example.com',
  title: null
}

interface Emphasis <: Parent {
  type: 'emphasis'
  children: [PhrasingContent]
}

Emphasis (Parent) represents stress emphasis of its contents.

Emphasis can be used where phrasing content is expected. Its content model is phrasing content.

For example, the following markdown:

*alpha* _bravo_

Yields:

{
  type: 'paragraph',
  children: [
    {
      type: 'emphasis',
      children: [{type: 'text', value: 'alpha'}]
    },
    {type: 'text', value: ' '},
    {
      type: 'emphasis',
      children: [{type: 'text', value: 'bravo'}]
    }
  ]
}

interface Heading <: Parent {
  type: 'heading'
  depth: 1 <= number <= 6
  children: [PhrasingContent]
}

Heading (Parent) represents a heading of a section.

Heading can be used where flow content is expected. Its content model is phrasing content.

A depth field must be present. A value of 1 is said to be the highest rank and 6 the lowest.

For example, the following markdown:

# Alpha

Yields:

{
  type: 'heading',
  depth: 1,
  children: [{type: 'text', value: 'Alpha'}]
}

interface HTML <: Literal {
  type: 'html'
}

HTML (Literal) represents a fragment of raw HTML.

HTML can be used where flow or phrasing content is expected. Its content is represented by its value field.

HTML nodes do not have the restriction of being valid or complete HTML ([HTML]) constructs.

For example, the following markdown:

<div>

Yields:

{type: 'html', value: '<div>'}

interface Image <: Node {
  type: 'image'
}

Image includes Resource
Image includes Alternative

Image (Node) represents an image.

Image can be used where phrasing content is expected. It has no content model, but is described by its alt field.

Image includes the mixins Resource and Alternative.

For example, the following markdown:

![alpha](https://example.com/favicon.ico "bravo")

Yields:

{
  type: 'image',
  url: 'https://example.com/favicon.ico',
  title: 'bravo',
  alt: 'alpha'
}

interface ImageReference <: Node {
  type: 'imageReference'
}

ImageReference includes Reference
ImageReference includes Alternative

ImageReference (Node) represents an image through association, or its original source if there is no association.

ImageReference can be used where phrasing content is expected. It has no content model, but is described by its alt field.

ImageReference includes the mixins Reference and Alternative.

ImageReference should be associated with a Definition.

For example, the following markdown:

![alpha][bravo]

Yields:

{
  type: 'imageReference',
  identifier: 'bravo',
  label: 'bravo',
  referenceType: 'full',
  alt: 'alpha'
}

interface InlineCode <: Literal {
  type: 'inlineCode'
}

InlineCode (Literal) represents a fragment of computer code, such as a file name, computer program, or anything a computer could parse.

InlineCode can be used where phrasing content is expected. Its content is represented by its value field.

This node relates to the flow content concept Code.

For example, the following markdown:

`foo()`

Yields:

{type: 'inlineCode', value: 'foo()'}

interface Link <: Parent {
  type: 'link'
  children: [PhrasingContent]
}

Link includes Resource

Link (Parent) represents a hyperlink.

Link can be used where phrasing content is expected. Its content model is also phrasing content.

Link includes the mixin Resource.

For example, the following markdown:

[alpha](https://example.com "bravo")

Yields:

{
  type: 'link',
  url: 'https://example.com',
  title: 'bravo',
  children: [{type: 'text', value: 'alpha'}]
}

interface LinkReference <: Parent {
  type: 'linkReference'
  children: [PhrasingContent]
}

LinkReference includes Reference

LinkReference (Parent) represents a hyperlink through association, or its original source if there is no association.

LinkReference can be used where phrasing content is expected. Its content model is also phrasing content.

LinkReference includes the mixin Reference.

LinkReferences should be associated with a Definition.

For example, the following markdown:

[alpha][Bravo]

Yields:

{
  type: 'linkReference',
  identifier: 'bravo',
  label: 'Bravo',
  referenceType: 'full',
  children: [{type: 'text', value: 'alpha'}]
}

interface List <: Parent {
  type: 'list'
  ordered: boolean?
  start: number?
  spread: boolean?
  children: [ListContent]
}

List (Parent) represents a list of items.

List can be used where flow content is expected. Its content model is list content.

An ordered field can be present. It represents that the items have been intentionally ordered (when true), or that the order of items is not important (when false or not present).

A start field can be present. It represents, when the ordered field is true, the starting number of the list.

A spread field can be present. It represents that one or more of its children are separated with a blank line from its siblings (when true), or not (when false or not present).

For example, the following markdown:

1. foo

Yields:

{
  type: 'list',
  ordered: true,
  start: 1,
  spread: false,
  children: [{
    type: 'listItem',
    spread: false,
    children: [{
      type: 'paragraph',
      children: [{type: 'text', value: 'foo'}]
    }]
  }]
}

interface ListItem <: Parent {
  type: 'listItem'
  spread: boolean?
  children: [FlowContent]
}

ListItem (Parent) represents an item in a List.

ListItem can be used where list content is expected. Its content model is flow content.

A spread field can be present. It represents that the item contains two or more children separated by a blank line (when true), or not (when false or not present).

For example, the following markdown:

* bar

Yields:

{
  type: 'listItem',
  spread: false,
  children: [{
    type: 'paragraph',
    children: [{type: 'text', value: 'bar'}]
  }]
}

interface Paragraph <: Parent {
  type: 'paragraph'
  children: [PhrasingContent]
}

Paragraph (Parent) represents a unit of discourse dealing with a particular point or idea.

Paragraph can be used where content is expected. Its content model is phrasing content.

For example, the following markdown:

Alpha bravo charlie.

Yields:

{
  type: 'paragraph',
  children: [{type: 'text', value: 'Alpha bravo charlie.'}]
}

interface Root <: Parent {
  type: 'root'
}

Root (Parent) represents a document.

Root can be used as the root of a tree, never as a child. Its content model is not limited to flow content, but instead can contain any mdast content with the restriction that all content must be of the same category.

interface Strong <: Parent {
  type: 'strong'
  children: [PhrasingContent]
}

Strong (Parent) represents strong importance, seriousness, or urgency for its contents.

Strong can be used where phrasing content is expected. Its content model is phrasing content.

For example, the following markdown:

**alpha** __bravo__

Yields:

{
  type: 'paragraph',
  children: [
    {
      type: 'strong',
      children: [{type: 'text', value: 'alpha'}]
    },
    {type: 'text', value: ' '},
    {
      type: 'strong',
      children: [{type: 'text', value: 'bravo'}]
    }
  ]
}

interface Text <: Literal {
  type: 'text'
}

Text (Literal) represents everything that is just text.

Text can be used where phrasing content is expected. Its content is represented by its value field.

For example, the following markdown:

Alpha bravo charlie.

Yields:

{type: 'text', value: 'Alpha bravo charlie.'}

interface ThematicBreak <: Node {
  type: 'thematicBreak'
}

ThematicBreak (Node) represents a thematic break, such as a scene change in a story, a transition to another topic, or a new document.

ThematicBreak can be used where flow content is expected. It has no content model.

For example, the following markdown:

***

Yields:

{type: 'thematicBreak'}

interface mixin Alternative {
  alt: string?
}

Alternative represents a node with a fallback

An alt field should be present. It represents equivalent content for environments that cannot represent the node as intended.

interface mixin Association {
  identifier: string
  label: string?
}

Association represents an internal relation from one node to another.

An identifier field must be present. It can match another node. identifier is a source value: character escapes and character references are not parsed. Its value must be normalized.

A label field can be present. label is a string value: it works just like title on a link or a lang on code: character escapes and character references are parsed.

To normalize a value, collapse markdown whitespace ([\t\n\r ]+) to a space, trim the optional initial and/or final space, and perform case-folding.

Whether the value of identifier (or normalized label if there is no identifier) is expected to be a unique identifier or not depends on the type of node including the Association. An example of this is that they should be unique on Definition, whereas multiple LinkReferences can be non-unique to be associated with one definition.

interface mixin Reference {
  referenceType: string
}

Reference includes Association

Reference represents a marker that is associated to another node.

A referenceType field must be present. Its value must be a referenceType. It represents the explicitness of the reference.

interface mixin Resource {
  url: string
  title: string?
}

Resource represents a reference to resource.

A url field must be present. It represents a URL to the referenced resource.

A title field can be present. It represents advisory information for the resource, such as would be appropriate for a tooltip.

enum referenceType {
  'shortcut' | 'collapsed' | 'full'
}

referenceType represents the explicitness of a reference.

• shortcut: the reference is implicit, its identifier inferred from its content
• collapsed: the reference is explicit, its identifier inferred from its content
• full: the reference is explicit, its identifier explicitly set

type MdastContent = FlowContent | ListContent | PhrasingContent

Each node in mdast falls into one or more categories of Content that group nodes with similar characteristics together.

type Content = Definition | Paragraph

Content represents runs of text that form definitions and paragraphs.

type FlowContent =
  Blockquote | Code | Heading | HTML | List | ThematicBreak | Content

Flow content represent the sections of document.

type ListContent = ListItem

List content represent the items in a list.

type PhrasingContent = Break | Emphasis | HTML | Image | ImageReference
  | InlineCode | Link | LinkReference | Strong | Text

Phrasing content represent the text in a document, and its markup.

Markdown syntax is often extended. It is not a goal of this specification to list all possible extensions. However, a short list of frequently used extensions are shown below.

The following interfaces are found in GitHub Flavored Markdown.

interface Delete <: Parent {
  type: 'delete'
  children: [PhrasingContent]
}

Delete (Parent) represents contents that are no longer accurate or no longer relevant.

Delete can be used where phrasing content is expected. Its content model is phrasing content.

For example, the following markdown:

~~alpha~~

Yields:

{
  type: 'delete',
  children: [{type: 'text', value: 'alpha'}]
}

interface ListItemGfm <: ListItem {
  checked: boolean?
}

In GFM, a checked field can be present. It represents whether the item is done (when true), not done (when false), or indeterminate or not applicable (when null or not present).

interface FootnoteDefinition <: Parent {
  type: 'footnoteDefinition'
  children: [FlowContent]
}

FootnoteDefinition includes Association

FootnoteDefinition (Parent) represents content relating to the document that is outside its flow.

FootnoteDefinition can be used where flow content is expected. Its content model is also flow content.

FootnoteDefinition includes the mixin Association.

FootnoteDefinition should be associated with FootnoteReferences.

For example, the following markdown:

[^alpha]: bravo and charlie.

Yields:

{
  type: 'footnoteDefinition',
  identifier: 'alpha',
  label: 'alpha',
  children: [{
    type: 'paragraph',
    children: [{type: 'text', value: 'bravo and charlie.'}]
  }]
}

interface FootnoteReference <: Node {
  type: 'footnoteReference'
}

FootnoteReference includes Association

FootnoteReference (Node) represents a marker through association.

FootnoteReference can be used where phrasing content is expected. It has no content model.

FootnoteReference includes the mixin Association.

FootnoteReference should be associated with a FootnoteDefinition.

For example, the following markdown:

[^alpha]

Yields:

{
  type: 'footnoteReference',
  identifier: 'alpha',
  label: 'alpha'
}

interface Table <: Parent {
  type: 'table'
  align: [alignType]?
  children: [TableContent]
}

Table (Parent) represents two-dimensional data.

Table can be used where flow content is expected. Its content model is table content.

The head of the node represents the labels of the columns.

An align field can be present. If present, it must be a list of alignTypes. It represents how cells in columns are aligned.

For example, the following markdown:

| foo | bar |
| :-- | :-: |
| baz | qux |

Yields:

{
  type: 'table',
  align: ['left', 'center'],
  children: [
    {
      type: 'tableRow',
      children: [
        {
          type: 'tableCell',
          children: [{type: 'text', value: 'foo'}]
        },
        {
          type: 'tableCell',
          children: [{type: 'text', value: 'bar'}]
        }
      ]
    },
    {
      type: 'tableRow',
      children: [
        {
          type: 'tableCell',
          children: [{type: 'text', value: 'baz'}]
        },
        {
          type: 'tableCell',
          children: [{type: 'text', value: 'qux'}]
        }
      ]
    }
  ]
}

interface TableCell <: Parent {
  type: 'tableCell'
  children: [PhrasingContent]
}

TableCell (Parent) represents a header cell in a Table, if its parent is a head, or a data cell otherwise.

TableCell can be used where row content is expected. Its content model is phrasing content excluding Break nodes.

For an example, see Table.

interface TableRow <: Parent {
  type: 'tableRow'
  children: [RowContent]
}

TableRow (Parent) represents a row of cells in a table.

TableRow can be used where table content is expected. Its content model is row content.

If the node is a head, it represents the labels of the columns for its parent Table.

For an example, see Table.

enum alignType {
  'left' | 'right' | 'center' | null
}

alignType represents how phrasing content is aligned ([CSSTEXT]).

• 'left': See the left value of the text-align CSS property
• 'right': See the right value of the text-align CSS property
• 'center': See the center value of the text-align CSS property
• null: phrasing content is aligned as defined by the host environment

type FlowContentGfm = FootnoteDefinition | Table | FlowContent

type ListContentGfm = ListItemGfm

type PhrasingContentGfm = FootnoteReference | Delete | PhrasingContent

type RowContent = TableCell

Row content represent the cells in a row.

type TableContent = TableRow

Table content represent the rows in a table.

The following interfaces are found with YAML.

interface YAML <: Literal {
  type: 'yaml'
}

YAML (Literal) represents a collection of metadata for the document in the YAML ([YAML]) data serialisation language.

YAML can be used where frontmatter content is expected. Its content is represented by its value field.

For example, the following markdown:

---
foo: bar
---

Yields:

{type: 'yaml', value: 'foo: bar'}

type FrontmatterContent = YAML

Frontmatter content represent out-of-band information about the document.

If frontmatter is present, it must be limited to one node in the tree, and can only exist as a head.

type FlowContentFrontmatter = FrontmatterContent | FlowContent

The following interfaces are found with footnotes (pandoc). Note that pandoc also uses FootnoteReference and FootnoteDefinition, but since GFM now supports footnotes, their definitions were moved to the GFM section

interface Footnote <: Parent {
  type: 'footnote'
  children: [PhrasingContent]
}

Footnote (Parent) represents content relating to the document that is outside its flow.

Footnote can be used where phrasing content is expected. Its content model is also phrasing content.

For example, the following markdown:

^[alpha bravo]

Yields:

{
  type: 'footnote',
  children: [{type: 'text', value: 'alpha bravo'}]
}

type PhrasingContentFootnotes = Footnote | PhrasingContent

See remark-mdx.

See the unist glossary.

See the unist list of utilities for more utilities.

• mdast-add-list-metadata — enhance the metadata of list and listItem nodes
• mdast-util-assert — assert nodes
• mdast-builder — build mdast structures with composable functions
• mdast-comment-marker — parse a comment marker
• mdast-util-compact — make a tree compact
• mdast-util-definitions — find definition nodes
• mdast-util-directive — parse and serialize directives
• mdast-util-find-and-replace — find and replace text
• mdast-flatten-image-paragraphs — flatten paragraph and image into one image node
• mdast-flatten-listitem-paragraphs — flatten listItem and (nested) paragraph into one listItem node
• mdast-flatten-nested-lists — transform a tree to avoid lists in lists
• mdast-util-from-adf — build mdast syntax tree from Atlassian Document Format (ADF)
• mdast-util-from-markdown — parse markdown
• mdast-util-frontmatter — parse and serialize frontmatter
• mdast-util-gfm — parse and serialize GFM
• mdast-util-gfm-autolink-literal — parse and serialize GFM autolink literals
• mdast-util-gfm-footnote — parse and serialize GFM footnotes
• mdast-util-gfm-strikethrough — parse and serialize GFM strikethrough
• mdast-util-gfm-table — parse and serialize GFM tables
• mdast-util-gfm-task-list-item — parse and serialize GFM task list items
• mdast-util-gridtables — parse and serialize gridtables
• mdast-util-heading-range — markdown heading as ranges
• mdast-util-heading-style — get the style of a heading node
• mdast-util-hidden — prevent nodes from being seen by transformers.
• mdast-util-math — parse and serialize math
• mdast-util-mdx — parse and serialize MDX
• mdast-util-mdx-expression — parse and serialize MDX expressions
• mdast-util-mdx-jsx — parse and serialize MDX JSX
• mdast-util-mdxjs-esm — parse and serialize MDX ESM
• mdast-move-images-to-root — move image nodes up the tree until they are direct children of the root
• mdast-normalize-headings — ensure at most one top-level heading is in the document
• mdast-util-phrasing — check if a node is phrasing content
• mdast-squeeze-paragraphs — remove empty paragraphs
• mdast-util-toc — generate a table of contents from a tree
• mdast-util-to-hast — transform to hast
• mdast-util-to-markdown — serialize markdown
• mdast-util-to-nlcst — transform to nlcst
• mdast-util-to-string — get the plain text content of a node
• mdast-zone — HTML comments as ranges or markers

• unist: Universal Syntax Tree. T. Wormer; et al.
• Markdown: Markdown. J. Gruber.
• CommonMark: CommonMark. J. MacFarlane; et al.
• GFM: GitHub Flavored Markdown. GitHub.
• HTML: HTML Standard, A. van Kesteren; et al. WHATWG.
• CSSTEXT: CSS Text, CSS Text, E. Etemad, K. Ishii. W3C.
• JavaScript: ECMAScript Language Specification. Ecma International.
• YAML: YAML Ain’t Markup Language, O. Ben-Kiki, C. Evans, I. döt Net.
• Web IDL: Web IDL, C. McCormack. W3C.

As mdast can contain HTML and be used to represent HTML, and improper use of HTML can open you up to a cross-site scripting (XSS) attack, improper use of mdast is also unsafe. When transforming to HTML (typically through hast), always be careful with user input and use hast-util-santize to make the hast tree safe.

• hast — Hypertext Abstract Syntax Tree format
• nlcst — Natural Language Concrete Syntax Tree format
• xast — Extensible Abstract Syntax Tree

See contributing.md in syntax-tree/.github for ways to get started. See support.md for ways to get help. Ideas for new utilities and tools can be posted in syntax-tree/ideas.

A curated list of awesome syntax-tree, unist, mdast, hast, xast, and nlcst resources can be found in awesome syntax-tree.

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

The initial release of this project was authored by @wooorm.

Special thanks to @eush77 for their work, ideas, and incredibly valuable feedback!

Thanks to @anandthakker, @arobase-che, @BarryThePenguin, @chinesedfan, @ChristianMurphy, @craftzdog, @d4rekanguok, @detj, @dominictarr, @gkatsev, @Hamms, @Hypercubed, @ikatyang, @izumin5210, @jasonLaster, @Justineo, @justjake, @KyleAMathews, @laysent, @macklinu, @mike-north, @Murderlon, @nevik, @Rokt33r, @rhysd, @rubys, @Sarah-Seo, @sethvincent, @silvenon, @simov, @staltz, @stefanprobst, @tmcw, and @vhf for contributing to mdast and related projects!

CC-BY-4.0 © Titus Wormer