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id plugins
description Using MDX plugins to expand Markdown functionality in CodeHarborHub
slug /markdown-features/plugins

MDX Plugins

CodeHarborHub uses MDX to power its documentation. Sometimes, you may want to extend or tweak Markdown syntax. For example:

  • Embed a YouTube video using image-like syntax: ![](https://youtu.be/example)
  • Style standalone links as social cards
  • Automatically prepend a copyright notice to every page

The answer is: create an MDX plugin!
MDX supports a powerful plugin system to customize how Markdown is parsed and transformed into JSX.

There are three common plugin use-cases:

How MDX Plugins Work

When Markdown is compiled, it goes through two intermediate steps:

  1. Markdown AST (MDAST)
  2. Hypertext AST (HAST)
  3. JSX Output

Plugins operate on these ASTs:

  • Remark → processes the Markdown AST
  • Rehype → processes the Hypertext AST

:::tip Use plugins to introduce shorter syntax for frequently used JSX elements.
For example, CodeHarborHub’s admonition blocks are powered by a Remark plugin. :::

Default Plugins

Docusaurus automatically injects a set of default Remark plugins during Markdown processing.
These handle tasks such as:

  • Generating a Table of Contents
  • Adding anchor links to each heading
  • Transforming images and links to require() calls

These built-in plugins are great examples to inspire your own custom plugins.

Installing Plugins

An MDX plugin is usually an npm package, so install it like any other dependency.

Example: adding math support:

npm install --save remark-math@5 rehype-katex@6
Remark vs Rehype in action
  • remark-math extracts $...$ math expressions from Markdown and transforms them into a JSX placeholder.
  • rehype-katex then takes those placeholders and renders them into KaTeX-powered HTML.

:::warning Many official Remark/Rehype plugins are ES Modules only. Docusaurus supports ESM, but we recommend using an ESM config file for easier imports. :::

Adding Plugins to docusaurus.config.js

Once installed, import and add the plugin to your config:

// highlight-start
import remarkMath from 'remark-math';
import rehypeKatex from 'rehype-katex';
// highlight-end

export default {
  presets: [
    [
      '@docusaurus/preset-classic',
      {
        docs: {
          remarkPlugins: [remarkMath],
          rehypePlugins: [rehypeKatex],
        },
      },
    ],
  ],
};

Using CommonJS? Dynamic imports make it work:

module.exports = async function createConfigAsync() {
  return {
    presets: [
      [
        '@docusaurus/preset-classic',
        {
          docs: {
            remarkPlugins: [(await import('remark-math')).default],
            rehypePlugins: [(await import('rehype-katex')).default],
          },
        },
      ],
    ],
  };
};

Configuring Plugins

Some plugins accept custom options. Use [plugin, options] syntax:

import rehypeKatex from 'rehype-katex';

export default {
  presets: [
    [
      '@docusaurus/preset-classic',
      {
        docs: {
          rehypePlugins: [
            [rehypeKatex, {strict: false}],
          ],
        },
      },
    ],
  ],
};

Check the plugin’s documentation for available options.

Creating Your Own Plugin

If no existing plugin fits your needs, you can create one. A plugin is a function that operates on the AST.

Example: prefix every h2 heading with Section X.

import {visit} from 'unist-util-visit';

const plugin = () => {
  return async (ast) => {
    let count = 1;
    visit(ast, 'heading', (node) => {
      if (node.depth === 2 && node.children.length > 0) {
        node.children.unshift({
          type: 'text',
          value: `Section ${count}. `,
        });
        count++;
      }
    });
  };
};

export default plugin;

Import and register it:

import sectionPrefix from './src/remark/section-prefix';

export default {
  presets: [
    [
      '@docusaurus/preset-classic',
      {
        docs: {
          remarkPlugins: [sectionPrefix],
        },
      },
    ],
  ],
};

:::tip The transformer function receives a second parameter, vfile, which provides metadata like the current Markdown file’s path. :::

Processing Order

By default, Docusaurus runs its internal plugins before your custom plugins. If you need to run your plugin first:

export default {
  presets: [
    [
      '@docusaurus/preset-classic',
      {
        docs: {
          beforeDefaultRemarkPlugins: [sectionPrefix],
        },
      },
    ],
  ],
};

This ensures your transformations (like heading prefixes) are included in generated tables of contents.