Add reading time

Create a remark plugin which adds a reading time property to the frontmatter of your Markdown or MDX files. Use this property to display the reading time for each page.

Recipe

1. Install the following packages: - [`reading-time`](https://www.npmjs.com/package/reading-time) to calculate minutes read - [`mdast-util-to-string`](https://www.npmjs.com/package/mdast-util-to-string) to extract all text from your markdown - [`@astrojs/markdown-remark`](https://www.npmjs.com/package/@astrojs/markdown-remark) to use [the `unified()` processor](/en/guides/markdown-content/#using-remark-and-rehype-plugins):

<PackageManagerTabs>
  <Fragment slot="npm">
  ```shell
npm install reading-time mdast-util-to-string @astrojs/markdown-remark
  ```
  </Fragment>
  <Fragment slot="pnpm">
  ```shell
pnpm add reading-time mdast-util-to-string @astrojs/markdown-remark
  ```
  </Fragment>
  <Fragment slot="yarn">
  ```shell
yarn add reading-time mdast-util-to-string @astrojs/markdown-remark
  ```
  </Fragment>
</PackageManagerTabs>

Create a remark plugin.

This plugin uses the mdast-util-to-string package to get the Markdown file's text. This text is then passed to the reading-time package to calculate the reading time in minutes.

import getReadingTime from 'reading-time';
import { toString } from 'mdast-util-to-string';

export function remarkReadingTime() {
  return function (tree, { data }) {
    const textOnPage = toString(tree);
    const readingTime = getReadingTime(textOnPage);
    // readingTime.text will give us minutes read as a friendly string,
    // i.e. "3 min read"
    data.astro.frontmatter.minutesRead = readingTime.text;
  };
}

Add the plugin to your config:

import { unified } from '@astrojs/markdown-remark';
import { defineConfig } from 'astro/config';
import { remarkReadingTime } from './remark-reading-time.mjs';

export default defineConfig({
  markdown: {
    processor: unified({
      remarkPlugins: [remarkReadingTime],
    }),
  },
});

Now all Markdown documents will have a calculated minutesRead property in their frontmatter.

Display Reading Time

If your blog posts are stored in a content collection, access the remarkPluginFrontmatter from the render(entry) function. Then, render minutesRead in your template wherever you would like it to appear.

---
import { getCollection, render } from 'astro:content';

export async function getStaticPaths() {
  const blog = await getCollection('blog');
  return blog.map(entry => ({
    params: { slug: entry.id },
    props: { entry },
  }));
}

const { entry } = Astro.props;
const { Content, remarkPluginFrontmatter } = await render(entry);
---

<html>
  <head>...</head>
  <body>
    ...
    <p>{remarkPluginFrontmatter.minutesRead}</p>
    ...
  </body>
</html>

If you're using a Markdown layout, use the minutesRead frontmatter property from Astro.props in your layout template.

---
const { minutesRead } = Astro.props.frontmatter;
---

<html>
  <head>...</head>
  <body>
    <p>{minutesRead}</p>
    <slot />
  </body>
</html>