# micromark-extension-frontmatter [![Build][build-badge]][build] [![Coverage][coverage-badge]][coverage] [![Downloads][downloads-badge]][downloads] [![Size][size-badge]][size] [![Sponsors][sponsors-badge]][collective] [![Backers][backers-badge]][collective] [![Chat][chat-badge]][chat] [micromark][] extensions to support frontmatter (YAML, TOML, and more). ## Contents * [What is this?](#what-is-this) * [When to use this](#when-to-use-this) * [Install](#install) * [Use](#use) * [API](#api) * [`frontmatter(options?)`](#frontmatteroptions) * [`frontmatterHtml(options?)`](#frontmatterhtmloptions) * [`toMatters(options?)`](#tomattersoptions) * [`Info`](#info) * [`Matter`](#matter) * [`Options`](#options) * [`Preset`](#preset) * [Examples](#examples) * [Authoring](#authoring) * [HTML](#html) * [CSS](#css) * [Syntax](#syntax) * [Types](#types) * [Compatibility](#compatibility) * [Security](#security) * [Related](#related) * [Contribute](#contribute) * [License](#license) ## What is this? This package contains two extensions that add support for frontmatter syntax as often used in markdown to [`micromark`][micromark]. Frontmatter is a metadata format in front of the content. It’s typically written in YAML and is often used with markdown. Frontmatter does not work everywhere so it makes markdown less portable. As there is no spec for frontmatter in markdown, these extensions follow how YAML frontmatter works on `github.com`. It can also parse TOML frontmatter, just like YAML except that it uses a `+`. ## When to use this You can use these extensions when you are working with [`micromark`][micromark] already. When you need a syntax tree, you can combine this package with [`mdast-util-frontmatter`][mdast-util-frontmatter]. All these packages are used [`remark-frontmatter`][remark-frontmatter], which focusses on making it easier to transform content by abstracting these internals away. ## Install This package is [ESM only][esm]. In Node.js (version 16+), install with [npm][]: ```sh npm install micromark-extension-frontmatter ``` In Deno with [`esm.sh`][esmsh]: ```js import {frontmatter, frontmatterHtml} from 'https://esm.sh/micromark-extension-frontmatter@2' ``` In browsers with [`esm.sh`][esmsh]: ```html ``` ## Use Say our module `example.js` looks as follows: ```js import {micromark} from 'micromark' import {frontmatter, frontmatterHtml} from 'micromark-extension-frontmatter' const output = micromark('---\na: b\n---\n# c', { extensions: [frontmatter()], htmlExtensions: [frontmatterHtml()] }) console.log(output) ``` …now running `node example.js` yields: ```html

c

``` ## API This package exports the identifiers [`frontmatter`][api-frontmatter], [`frontmatterHtml`][api-frontmatter-html], and [`toMatters`][api-to-matters]. There is no default export. The export map supports the [`development` condition][development]. Run `node --conditions development module.js` to get instrumented dev code. Without this condition, production code is loaded. ### `frontmatter(options?)` Create an extension for [`micromark`][micromark] to enable frontmatter syntax. ###### Parameters * `options` ([`Options`][api-options], default: `['yaml']`) — configuration ###### Returns Extension for `micromark` that can be passed in `extensions`, to enable frontmatter syntax ([`Extension`][micromark-extension]). ### `frontmatterHtml(options?)` Create an extension for `micromark` to support frontmatter when serializing to HTML. > 👉 **Note**: this makes sure nothing is generated in the output HTML for > frontmatter. ###### Parameters * `options` ([`Options`][api-options], default: `['yaml']`) — configuration ###### Returns Extension for `micromark` that can be passed in `htmlExtensions`, to support frontmatter when serializing to HTML ([`HtmlExtension`][micromark-html-extension]). ### `toMatters(options?)` Simplify options by normalizing them to an array of matters. ###### Parameters * `options` ([`Options`][api-options], default: `['yaml']`) — configuration ###### Returns List of matters ([`Array`][api-matter]). ### `Info` Sequence (TypeScript type). Depending on how this structure is used, it reflects a marker or a fence. ###### Fields * `open` (`string`) — opening * `close` (`string`) — closing ### `Matter` Fields describing a kind of matter (TypeScript type). > 👉 **Note**: using `anywhere` is a terrible idea. > It’s called frontmatter, not matter-in-the-middle or so. > This makes your markdown less portable. > 👉 **Note**: `marker` and `fence` are mutually exclusive. > If `marker` is set, `fence` must not be set, and vice versa. ###### Fields * `type` (`string`) — node type to tokenize as * `marker` (`string` or [`Info`][api-info]) — character repeated 3 times, used as complete fences * `fence` (`string` or [`Info`][api-info]) — complete fences * `anywhere` (`boolean`, default: `false`) — whether matter can be found anywhere in the document, normally only matter at the start of the document is recognized ### `Options` Configuration (TypeScript type). ###### Type ```ts type Options = Array | Matter | Preset ``` ### `Preset` Known name of a frontmatter style (TypeScript type). * `'yaml'` — [`Matter`][api-matter] defined as `{type: 'yaml', marker: '-'}` * `'toml'` — [`Matter`][api-matter] defined as `{type: 'toml', marker: '+'}` ###### Type ```ts type Preset = 'toml' | 'yaml' ``` ## Examples Here are a couple of example of different matter objects and what frontmatter they match. To match frontmatter with the same opening and closing fence, namely three of the same markers, use for example `{type: 'yaml', marker: '-'}`, which matches: ```yaml --- key: value --- ``` To match frontmatter with different opening and closing fences, which each use three different markers, use for example `{type: 'custom', marker: {open: '<', close: '>'}}`, which matches: ```text <<< data >>> ``` To match frontmatter with the same opening and closing fences, which both use the same custom string, use for example `{type: 'custom', fence: '+=+=+=+'}`, which matches: ```text +=+=+=+ data +=+=+=+ ``` To match frontmatter with different opening and closing fences, which each use different custom strings, use for example `{type: 'json', fence: {open: '{', close: '}'}}`, which matches: ```json { "key": "value" } ``` ## Authoring When authoring markdown with frontmatter, it’s recommended to use YAML frontmatter if possible. While YAML has some warts, it works in the most places, so using it guarantees the highest chance of portability. In certain ecosystems, other flavors are widely used. For example, in the Rust ecosystem, TOML is often used. In such cases, using TOML is an okay choice. When possible, do not use other types of frontmatter, and do not allow frontmatter anywhere. ## HTML Frontmatter does not relate to HTML elements. It is typically stripped, which is what these extensions do. ## CSS This package does not relate to CSS. ## Syntax Frontmatter forms with the following BNF: ```bnf frontmatter ::= fence_open *( eol *line ) eol fence_close fence_open ::= sequence_open *space_or_tab fence_close ::= sequence_close *space_or_tab ; Note: options can define custom sequences. sequence_open ::= 3'+' | 3'-' ; Note: options can define custom sequences. ; Restriction: `sequence_close` must correspond to `sequence_open`. sequence_close ::= 3'+' | 3'-' ; Character groups for informational purposes. byte ::= 0x00..=0xFFFF eol ::= '\n' | '\r' | '\r\n' line ::= byte - eol ``` Frontmatter can only occur once. It cannot occur in a container. It must have a closing fence. Like flow constructs, it must be followed by an eol (line ending) or eof (end of file). ## Types This package is fully typed with [TypeScript][]. It exports the additional types [`Info`][api-info], [`Matter`][api-matter], [`Options`][api-options], [`Preset`][api-preset]. ## Compatibility Projects maintained by the unified collective are compatible with maintained versions of Node.js. When we cut a new major release, we drop support for unmaintained versions of Node. This means we try to keep the current release line, `micromark-extension-frontmatter@^2`, compatible with Node.js 16. This package works with `micromark` version `3` and later. ## Security This package is safe. ## Related * [`remark-frontmatter`][remark-frontmatter] — remark plugin using this to support frontmatter * [`mdast-util-frontmatter`][mdast-util-frontmatter] — mdast utility to support frontmatter ## Contribute See [`contributing.md` in `micromark/.github`][contributing] for ways to get started. See [`support.md`][support] for ways to get help. This project has a [code of conduct][coc]. By interacting with this repository, organization, or community you agree to abide by its terms. ## License [MIT][license] © [Titus Wormer][author] [build-badge]: https://github.com/micromark/micromark-extension-frontmatter/workflows/main/badge.svg [build]: https://github.com/micromark/micromark-extension-frontmatter/actions [coverage-badge]: https://img.shields.io/codecov/c/github/micromark/micromark-extension-frontmatter.svg [coverage]: https://codecov.io/github/micromark/micromark-extension-frontmatter [downloads-badge]: https://img.shields.io/npm/dm/micromark-extension-frontmatter.svg [downloads]: https://www.npmjs.com/package/micromark-extension-frontmatter [size-badge]: https://img.shields.io/badge/dynamic/json?label=minzipped%20size&query=$.size.compressedSize&url=https://deno.bundlejs.com/?q=micromark-extension-frontmatter [size]: https://bundlejs.com/?q=micromark-extension-frontmatter [sponsors-badge]: https://opencollective.com/unified/sponsors/badge.svg [backers-badge]: https://opencollective.com/unified/backers/badge.svg [collective]: https://opencollective.com/unified [chat-badge]: https://img.shields.io/badge/chat-discussions-success.svg [chat]: https://github.com/micromark/micromark/discussions [npm]: https://docs.npmjs.com/cli/install [esmsh]: https://esm.sh [license]: license [author]: https://wooorm.com [contributing]: https://github.com/micromark/.github/blob/main/contributing.md [support]: https://github.com/micromark/.github/blob/main/support.md [coc]: https://github.com/micromark/.github/blob/main/code-of-conduct.md [esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c [typescript]: https://www.typescriptlang.org [development]: https://nodejs.org/api/packages.html#packages_resolving_user_conditions [micromark]: https://github.com/micromark/micromark [mdast-util-frontmatter]: https://github.com/syntax-tree/mdast-util-frontmatter [remark-frontmatter]: https://github.com/remarkjs/remark-frontmatter [micromark-extension]: https://github.com/micromark/micromark#syntaxextension [micromark-html-extension]: https://github.com/micromark/micromark#htmlextension [api-frontmatter]: #frontmatteroptions [api-frontmatter-html]: #frontmatterhtmloptions [api-to-matters]: #tomattersoptions [api-info]: #info [api-matter]: #matter [api-options]: #options [api-preset]: #preset

c	File Name	Size	T	Date
zip	dev/	4096	---	2026-06-10 03:36:21
zip	lib/	4096	---	2026-06-10 03:36:21
-	index.d.ts	366	ts	2026-05-20 11:21:44
-	index.js	480	js	2026-05-20 11:21:44
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-	package.json	2462	json	2026-05-20 11:21:44
-	readme.md	11475	md	2026-05-20 11:21:44

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