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Using Markdoc with HTML and Web Components

Markdoc supports rendering Markdoc syntax into HTML with the HTML renderer.

To get started with the HTML renderer, check out this example repo for how to use Markdoc with express and Web Components. You can use the HTML renderer without Web Components to transform and render HTML, but we recommend using Web Components as a way to organize and encapsulate functionality for custom Markdoc components.


This guide assumes that you have an Express app installed. If you're starting from scratch, follow these instructions to install Express and create an app.

  1. Set up a Markdoc schema.

    ├── Callout.markdoc.js
    └── heading.markdoc.js
    // [schema/Callout.markdoc.js](
    module.exports = {
      render: 'markdoc-callout',
      description: 'Display the enclosed content in a callout box',
      children: ['paragraph'],
      attributes: {
        type: {
          type: String,
          default: 'note',
          matches: ['check', 'error', 'note', 'warning'],
            'Controls the color and icon of the callout. Can be: "caution", "check", "note", "warning"'
    // [schema/heading.markdoc.js](
    const { nodes } = require('@markdoc/markdoc');
    function generateID(children, attributes) {
      if ( && typeof === 'string') {
      return children
        .filter((child) => typeof child === 'string')
        .join(' ')
        .replace(/[?]/g, '')
        .replace(/\s+/g, '-')
    module.exports = {
      transform(node, config) {
        const base = nodes.heading.transform(node, config); = generateID(base.children, base.attributes);
        return base;
  2. Define a component for any custom tag. Since heading is a core Markdown node, Markdoc already knows how to render it using the CommonMark spec. Callout needs a component since it's a custom tag. We used lit in our example to define a Web Component for the markdoc-callout element.

    // [src/Callout.js](
    import { html, css, LitElement } from 'lit';
    export class MarkdocCallout extends LitElement {
      static styles = css`
        .note {
          background-color: #8792a2;
        .caution {
          background-color: #d97917;
        .check {
          background-color: #000000;
        .warning {
          background-color: #ed5f74;
      static properties = {
        type: { type: String }
      constructor() {
        this.type = 'note';
      render() {
        return html`<p class="${this.type}"><slot></slot></p>`;
  3. Parse your Markdoc documents on the server to create a map of your routes and Markdoc content. We call this a "content manifest" which is used during a request to return the right Markdoc content for the route.

    // [...](
    const rawText = fs.readFileSync(file, 'utf-8');
    const ast = Markdoc.parse(rawText);
  4. Call Markdoc.transform on the server with a config of your custom tags, nodes, and any variables you want your Markdoc content to access. Then, use the HTML Markdoc renderer (Markdoc.renderers.html) to render the transformed content into the HTML to display to your user.

    // [server.js](
    const express = require('express');
    const app = express();
    const callout = require('./schema/callout.markdoc');
    const heading = require('./schema/heading.markdoc');
    // [...](
    app.get('/markdoc', (req, res) => {
      const ast = contentManifest[req.query.path];
      const config = {
        tags: {
        nodes: {
        variables: {}
      const content = Markdoc.transform(ast, config);
      const rendered = Markdoc.renderers.html(content) || '';
      const html = TEMPLATE.replace(/{{ CONTENT }}/, rendered);
      return res.send(html);
    app.listen(4242, () => {
      console.log(`Example app listening on port ${4242}`);
  5. Make sure to include any bundled scripts (in this case main.js) with your custom components on the client. This example uses a simple HTML template to inject the Markdoc content, but you can use other templating engines (for example: Pug, Handlebars, and so on) to manage this content injection for you.

    <!DOCTYPE html>
    <html lang="en">
        <meta charset="utf-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1" />
        <meta name="description" content="Web site created using Markdoc" />
        <title>Markdoc: Create HTML Example</title>
        {{ CONTENT }}
        <script src="./main.js"></script>
  6. Start the demo app.

    npm run build


    npm run start