[unified](https://unifiedjs.com) enables new exciting projects like [Gatsby](https://gatsbyjs.org) to pull in Markdown, [MDX](https://mdxjs.com) to embed JSX, and [Prettier](https://prettier.io) to format it. It’s used in about 300k projects on GitHub and has about 10m downloads each month on npm.

unified uses abstract syntax trees, or ASTs, that plugins can operate on. It can even process between different formats. This means you can parse a markdown document, transform it to HTML, and then transpile back to markdown.

unified leverages a syntax tree specification (called unist or UST) so that utilities can be shared amongst different formats. In practice, you can use unist-util-visit to visit nodes using the same library with the same API on any supported AST.

You can use the remark CLI to inspect the AST, run plugins, or lint your markdown documents. It can be used in your build scripts to generate HTML or ensure your markdown style guide is adhered to.

- Inspect the AST: `remark document.md --inspect`
- Use a plugin: `remark document.md --use toc`
- Overwrite your document after the plugin runs: `remark document.md --use toc -o`
- Lint a document: `remark document.md --frail --use preset-lint-markdown-style-guide`

Introduction to the remark CLI

Manually maintaining a table of contents in markdown documents can be a lot of work. By combining [remark-toc](https://github.com/remarkjs/remark-toc) and [remark-slug](https://github.com/remarkjs/remark-toc) you can ensure generate your table of contents and ensure it's always up to date.

Add a Dynamic Table of Contents to Your Markdown Documents with remark-toc

Most of the time with markdown documents we want to render them to HTML for static websites. You can use remark and the [remark-html](https://github.com/remarkjs/remark-html) plugin to transpile your markdown documents to HTML with a build script.

Convert Markdown to HTML with remark-html

[remark](https://github.com/remarkjs/remark) is a pluggable markdown parser and compiler. It's part of the [unified](https://unifiedjs.com) so it offers a wide array of libraries to make writing plugins with the markdown AST ([MDAST](https://github.com/syntax-tree/mdast)) more developer friendly.

We'll use `unist-util-visit` to traverse heading nodes in a Markdown file and prefix all `h1`s with the text "BREAKING" using a TDD workflow.

Create a remark Plugin to Modify Markdown Headings

When using remark to manipulate markdown documents, you can use [unist-util-remove](https://www.npmjs.com/package/unist-util-remove) to remove nodes of a particular type. You can combine it with [unist-util-visit](https://www.npmjs.com/package/unist-util-remove) to remove nodes based on their parent's context in the AST.

In this example, we remove all images contained within heading nodes.

Remove Markdown Nodes from a Document with unist-util-remove

You can use unified's [virtual file](https://github.com/vfile) to add data from a document in order to use it elsewhere. In this lesson we'll store metadata from all heading nodes in a markdown document using remark and vfile.

unified - the compiler for your content

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