Use Mermaid in Markdown to draw diagrams.

1. Mermaid

Mermaid a simple markdown-like script language for generating charts from text via javascript.

1.1 Using Mermaid in Web Page

1.2 Using Mermaid in Markdown

You can use Jekyll plugin jekyll-mermaid to create diagrams and flowcharts with markdown in your local Jekyll. For example, define a flowchart with 4 nodes as follows.

graph TD;

It looks like this.

graph TD; A-->B; A-->C; B-->D; C-->D;

However, this plugin is not officially supported by GitHub Pages. The above markdown diagram definition won’t work if you push it to GitHub Pages.

1.3 GitHub Pages

Unfortunately, GitHub Pages currently doesn’t support Mermaid, see the issue. The workaround is to use html tag directly in markdown file. Instead of using the code block, we can wrap the diagram definition into a <div> tag. The following definition of a flowchart works in GitHub Pages.

<div class="mermaid">
graph TD;

The following sections will introduce the details of how to generate diagram in markdown and let it work in GitHub Pages as well.

2. Using Mermaid in Jekyll

2.1 Page Template

Create a file named with mermaid.html in _include directory as follows:

<script type="text/javascript"
$(document).ready(function() {
        theme: 'forest'
  • Go to to search the latest version or specific version.
  • Go to to check available themes.

Update file _inlude/head.html, include the above template file if page.mermaid is true.

{% if page.mermaid %}
  {% include mermaid.html %}
{% endif %}

2.2 Creating Diagram Definition in Markdown Page

In order to use Mermaid in markdown page, it must have a variable mermaid and set its value to true. For example, the following example is a markdown page using mermaid.

layout: post
key: blog
title: "Generating Diagrams with Mermaid in Markdown"
date: 2018-09-15
tags: [Mermaid]
mermaid: true

1) Example One:

<div class="mermaid">
graph LR
    A --- B
graph LR A --- B B-->C[Happy] B-->D(Sad);

2) Example Two:

<div class="mermaid">
    graph TD
      B-->C[fa:fa-ban forbidden]
      B-->E(fa:fa-camera-retro perhaps?);
graph TD B[peace] B-->C[fa:fa-ban forbidden] B-->D(fa:fa-spinner); B-->E(fa:fa-camera-retro perhaps?);

AI Instructions

Setting up Jekyll to use the Mermaid diagram tool involves a few steps. Here’s a guide to help you through the process:

1. Install Jekyll (if you haven’t already)

First, ensure you have Jekyll installed. You can install it by running:

gem install jekyll bundler

2. Create a New Jekyll Site (if needed)

If you’re starting from scratch, create a new Jekyll site:

jekyll new my-awesome-site
cd my-awesome-site

3. Install Mermaid

Mermaid can be included in Jekyll sites via a JavaScript file. You need to add the Mermaid JS to your site.

Option 1: Using a CDN

Add the following line to your HTML layout (usually in _layouts/default.html):

<script src=""></script>

Option 2: Download and Host

  1. Download mermaid.min.js from the Mermaid GitHub repository.
  2. Place it in an accessible directory in your Jekyll site, like /assets/js/.
  3. Link to it in your HTML layout:
<script src="/assets/js/mermaid.min.js"></script>

4. Initialize Mermaid

You can initialize Mermaid by adding a script tag at the bottom of your layout file (_layouts/default.html), just before the closing </body> tag:


5. Add Mermaid Diagrams in Your Content

You can now add Mermaid diagrams directly in your Markdown files. Use code blocks with mermaid as the language identifier:

graph TD;

6. Build and Serve Your Site

Finally, build and serve your Jekyll site:

bundle exec jekyll serve


  • Check JavaScript Console: If Mermaid diagrams aren’t rendering, check your browser’s JavaScript console for errors.
  • Syntax Errors in Diagrams: Ensure your Mermaid syntax is correct. Invalid syntax can prevent diagrams from rendering.

Additional Customization

  • Mermaid Configuration: Mermaid offers various configuration options. You can customize these in the initialization script.
  • Styling: You can apply custom CSS to style your Mermaid diagrams.

By following these steps, you should be able to integrate Mermaid diagrams into your Jekyll site. Remember to regularly check for updates to the Mermaid library to ensure compatibility and security.

3. References