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Markdown and MDX

Markdown is a lightweight markup language used to format text. It allows you to write using plain text syntax and convert it to structurally valid HTML. It's commonly used for writing content on websites and blogs.

You write...

I **love** using [Next.js](https://nextjs.org/)

Output:

<p>I <strong>love</strong> using <a href="https://nextjs.org/">Next.js</a></p>

MDX is a superset of markdown that lets you write JSX directly in your markdown files. It is a powerful way to add dynamic interactivity and embed React components within your content.

Next.js can support both local MDX content inside your application, as well as remote MDX files fetched dynamically on the server. The Next.js plugin handles transforming markdown and React components into HTML, including support for usage in Server Components (the default in App Router).

@next/mdx

The @next/mdx package is used to configure Next.js so it can process markdown and MDX. It sources data from local files, allowing you to create pages with a .mdx extension, directly in your /pages or /app directory.

Let's walk through how to configure and use MDX with Next.js.

Getting Started

Install packages needed to render MDX:

Terminal
npm install @next/mdx @mdx-js/loader @mdx-js/react @types/mdx

Create a mdx-components.tsx file at the root of your application (src/ or the parent folder of app/):

Good to know: mdx-components.tsx is required to use MDX with App Router and will not work without it.

mdx-components.tsx
import type { MDXComponents } from 'mdx/types'
 
export function useMDXComponents(components: MDXComponents): MDXComponents {
  return {
    ...components,
  }
}

Update the next.config.js file at your project's root to configure it to use MDX:

next.config.js
const withMDX = require('@next/mdx')()
 
/** @type {import('next').NextConfig} */
const nextConfig = {
  // Configure `pageExtensions` to include MDX files
  pageExtensions: ['js', 'jsx', 'mdx', 'ts', 'tsx'],
  // Optionally, add any other Next.js config below
}
 
module.exports = withMDX(nextConfig)

Then, create a new MDX page within the /app directory:

  your-project
  ├── app
  │   └── my-mdx-page
  │       └── page.mdx
  └── package.json

Now you can use markdown and import React components directly inside your MDX page:

import { MyComponent } from 'my-components'
 
# Welcome to my MDX page!
 
This is some **bold** and _italics_ text.
 
This is a list in markdown:
 
- One
- Two
- Three
 
Checkout my React component:
 
<MyComponent />

Navigating to the /my-mdx-page route should display your rendered MDX.

Remote MDX

If your markdown or MDX files or content lives somewhere else, you can fetch it dynamically on the server. This is useful for content stored in a separate local folder, CMS, database, or anywhere else. A popular community package for this use is next-mdx-remote.

Good to know: Please proceed with caution. MDX compiles to JavaScript and is executed on the server. You should only fetch MDX content from a trusted source, otherwise this can lead to remote code execution (RCE).

The following example uses next-mdx-remote:

app/my-mdx-page-remote/page.tsx
import { MDXRemote } from 'next-mdx-remote/rsc'
 
export default async function RemoteMdxPage() {
  // MDX text - can be from a local file, database, CMS, fetch, anywhere...
  const res = await fetch('https://...')
  const markdown = await res.text()
  return <MDXRemote source={markdown} />
}

Navigating to the /my-mdx-page-remote route should display your rendered MDX.

Layouts

To share a layout amongst MDX pages, you can use the built-in layouts support with the App Router.

app/my-mdx-page/layout.tsx
export default function MdxLayout({ children }: { children: React.ReactNode }) {
  // Create any shared layout or styles here
  return <div style={{ color: 'blue' }}>{children}</div>
}

Remark and Rehype Plugins

You can optionally provide remark and rehype plugins to transform the MDX content.

For example, you can use remark-gfm to support GitHub Flavored Markdown.

Since the remark and rehype ecosystem is ESM only, you'll need to use next.config.mjs as the configuration file.

next.config.mjs
import remarkGfm from 'remark-gfm'
import createMDX from '@next/mdx'
 
/** @type {import('next').NextConfig} */
const nextConfig = {
  // Configure `pageExtensions`` to include MDX files
  pageExtensions: ['js', 'jsx', 'mdx', 'ts', 'tsx'],
  // Optionally, add any other Next.js config below
}
 
const withMDX = createMDX({
  // Add markdown plugins here, as desired
  options: {
    remarkPlugins: [remarkGfm],
    rehypePlugins: [],
  },
})
 
// Merge MDX config with Next.js config
export default withMDX(nextConfig)

Frontmatter

Frontmatter is a YAML like key/value pairing that can be used to store data about a page. @next/mdx does not support frontmatter by default, though there are many solutions for adding frontmatter to your MDX content, such as:

To access page metadata with @next/mdx, you can export a metadata object from within the .mdx file:

export const metadata = {
  author: 'John Doe',
}
 
# My MDX page

Custom Elements

One of the pleasant aspects of using markdown, is that it maps to native HTML elements, making writing fast, and intuitive:

This is a list in markdown:
 
- One
- Two
- Three

The above generates the following HTML:

<p>This is a list in markdown:</p>
 
<ul>
  <li>One</li>
  <li>Two</li>
  <li>Three</li>
</ul>

When you want to style your own elements for a custom feel to your website or application, you can pass in shortcodes. These are your own custom components that map to HTML elements.

To do this, open the mdx-components.tsx file at the root of your application and add custom elements:

mdx-components.tsx
import type { MDXComponents } from 'mdx/types'
import Image, { ImageProps } from 'next/image'
 
// This file allows you to provide custom React components
// to be used in MDX files. You can import and use any
// React component you want, including inline styles,
// components from other libraries, and more.
 
export function useMDXComponents(components: MDXComponents): MDXComponents {
  return {
    // Allows customizing built-in components, e.g. to add styling.
    h1: ({ children }) => <h1 style={{ fontSize: '100px' }}>{children}</h1>,
    img: (props) => (
      <Image
        sizes="100vw"
        style={{ width: '100%', height: 'auto' }}
        {...(props as ImageProps)}
      />
    ),
    ...components,
  }
}

Deep Dive: How do you transform markdown into HTML?

React does not natively understand markdown. The markdown plaintext needs to first be transformed into HTML. This can be accomplished with remark and rehype.

remark is an ecosystem of tools around markdown. rehype is the same, but for HTML. For example, the following code snippet transforms markdown into HTML:

import { unified } from 'unified'
import remarkParse from 'remark-parse'
import remarkRehype from 'remark-rehype'
import rehypeSanitize from 'rehype-sanitize'
import rehypeStringify from 'rehype-stringify'
 
main()
 
async function main() {
  const file = await unified()
    .use(remarkParse) // Convert into markdown AST
    .use(remarkRehype) // Transform to HTML AST
    .use(rehypeSanitize) // Sanitize HTML input
    .use(rehypeStringify) // Convert AST into serialized HTML
    .process('Hello, Next.js!')
 
  console.log(String(file)) // <p>Hello, Next.js!</p>
}

The remark and rehype ecosystem contains plugins for syntax highlighting, linking headings, generating a table of contents, and more.

When using @next/mdx as shown above, you do not need to use remark or rehype directly, as it is handled for you. We're describing it here for a deeper understanding of what the @next/mdx package is doing underneath.

Using the Rust-based MDX compiler (Experimental)

Next.js supports a new MDX compiler written in Rust. This compiler is still experimental and is not recommended for production use. To use the new compiler, you need to configure next.config.js when you pass it to withMDX:

next.config.js
module.exports = withMDX({
  experimental: {
    mdxRs: true,
  },
})