This is a remark plugin that adds Obsidian-like callout syntax.

Note that this is not a transformer plugin. Instead, under the hood it adds syntax extensions to micromark, which is the markdown parser used in remark.

Issues and pull requests are welcomed!

• Support nested callouts.

• Support markdown formatted elements inside your callout titles, for example, code, emphasis, heading, math, etc.

You can install this package via npm or pnpm.

# install using npm
npm install remark-callout

# install using pnpm
pnpm install remark-callout

import { unified } from 'unified';
import remarkParse from 'remark-parse';
import remarkRehype from 'remark-rehype';
import rehypeStringify from 'rehype-stringify';

import remarkCallout from 'remark-callout';

const md = `
> [!warning] \`sudo rm -rf\` is *dangerous*!
> Although this simple command can help you easily remove a folder, this command should be used with extra care.
`;

const file = unified()
  .use(remarkParse)
  .use(remarkCallout)
  .use(remarkRehype)
  .use(rehypeStringify)
  .processSync(md);
console.log(String(file));

The generated HTML of the above code would be

<blockquote class="callout warning">
  <div class="callout-title warning">
    <span class="callout-icon">
      <svg
        xmlns="http://www.w3.org/2000/svg"
        width="16"
        height="16"
        viewBox="0 0 24 24"
        fill="none"
        stroke="currentColor"
        stroke-width="2"
        stroke-linecap="round"
        stroke-linejoin="round"
        class="lucide-alert-triangle"
      >
        <path d="M10.29 3.86 1.82 18a2 2 0 0 0 1.71 3h16.94a2 2 0 0 0 1.71-3L13.71 3.86a2 2 0 0 0-3.42 0z"></path>
        <line x1="12" y1="9" x2="12" y2="13"></line>
        <line x1="12" y1="17" x2="12.01" y2="17"></line>
      </svg>
    </span>
    <p>
      <code>sudo rm -rf</code> is <em>dangerous</em>!
    </p>
  </div>
  <div class="callout-content">
    <p>
      Although this simple command can help you easily remove a folder, this
      command should be used with extra care.
    </p>
  </div>
</blockquote>

Class names are embedded in the generated HTML, so that CSS rules can be used to adjust the style.

As can be seen from above, by default the blockquote element is used to hold the callout; also, default icons are chosen for different callout types. This can be changed by adding configurations.

You can pass configuration object to remarkCallout. For example, to change the SVG string for the callout type warning and change the callout container to div, you can change the above code to

const config = {
    callouts: {
        warning: {
            svg: `<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-alarm-clock"><circle cx="12" cy="13" r="8"/><path d="M12 9v4l2 2"/><path d="M5 3 2 6"/><path d="m22 6-3-3"/><path d="M6.38 18.7 4 21"/><path d="M17.64 18.67 20 21"/></svg>`
        }
    },
    calloutContainer: "div"
};

const file = unified()
  .use(remarkParse)
  .use(remarkCallout, config)
  .use(remarkRehype)
  .use(rehypeStringify)
  .processSync(md);
console.log(String(file));

Then, the generated HTML would be changed to

<div class="callout warning">
  <div class="callout-title warning">
    <span class="callout-icon">
      <svg
        xmlns="http://www.w3.org/2000/svg"
        width="24"
        height="24"
        viewBox="0 0 24 24"
        fill="none"
        stroke="currentColor"
        stroke-width="2"
        stroke-linecap="round"
        stroke-linejoin="round"
        class="lucide lucide-alarm-clock"
      >
        <circle cx="12" cy="13" r="8"></circle>
        <path d="M12 9v4l2 2"></path>
        <path d="M5 3 2 6"></path>
        <path d="m22 6-3-3"></path>
        <path d="M6.38 18.7 4 21"></path>
        <path d="M17.64 18.67 20 21"></path>
      </svg>
    </span>
    <p>
      <code>sudo rm -rf</code> is <em>dangerous</em>!
    </p>
  </div>
  <div class="callout-content">
    <p>
      Although this simple command can help you easily remove a folder, this
      command should be used with extra care.
    </p>
  </div>
</div>

The configuration object is of type:

type SingleCalloutConfig = {
    svg?: string,
    // Will be embeded as inline style of the icon. Deprecated.
    // Only take effect when embedDefaultColor is set to true.
    // It is considered best to adjust the color using the provided class names
    // and CSS rules.
    color?: string
};

type Config = {
    callouts?: {
        note?: SingleCalloutConfig,
        tip?: SingleCalloutConfig,
        warning?: SingleCalloutConfig,
        abstract?: SingleCalloutConfig,
        info?: SingleCalloutConfig,
        todo?: SingleCalloutConfig,
        success?: SingleCalloutConfig,
        question?: SingleCalloutConfig,
        danger?: SingleCalloutConfig,
        bug?: SingleCalloutConfig,
        example?: SingleCalloutConfig,
        failure?: SingleCalloutConfig,
        quote?: SingleCalloutConfig
    },
    calloutContainer?: string,  // set the container element type for callouts
    embedDefaultColor?: boolean,   // defaults to false
    customClassNames?: string[],  // add more class names to the callout container
}

For unspecified parts, this package will use the default. Please check lib/config.ts for defaultConfig.

Another example:

> [!note] Change $\alpha_k$ adaptively
> One way to increase the performance of our model is to let the optimizer change $\alpha_k$ adaptively.

The render result:

Of course, you can adjust the CSS to make it appeal to your taste.

This plugin offers some default behavior, such as the callout icon and callout title.

Some customization can be achieved through configuration.

As this is a remark plugin, you can easily add this into your Astro project. Just add this plugin into astro.config.mjs file, inside the remarkPlugins property.

There are some existing remark plugins for Obsidian-like callouts, including @portaljs/remark-callouts, remark-callouts, and remark-obsidian-callout. The behavior of these plugins is not satisfactory for me, though. In fact, @portaljs/remark-callouts's callouts only support plain text callout title (to my knowledge, remark-callouts is the same but deprecated version of @portaljs/remark-callouts), such as

> [!note] This is a plain text title.
> blablabla...

And remark-obsidian-callout will transform formatted text into plain text that is in the callout title.

But inside Obsidian, callouts' titles are parsed as formatted elements, and as a result it supports including heading, code segments, math, etc. in the callout title:

> [!note] ##### The *Euler* formula: $e^{i \pi} + 1 = 0$
> As we know, the Euler formula is ...

In Obsidian, he above markdown segment will be rendered as which makes callouts more powerful and useful.

The plugins @portaljs/remark-callouts and remark-obsidian-callouts are actually transformers. In comparison, this plugin provides syntax, html, and mdast util extensions to let remark support callouts.

This plugin, in contrast, supports formatted elements inside a callout title.

• Maybe Collapsible callouts?

MIT license.