sphinxcontrib-mermaid

August 3, 2026 · View on GitHub

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This extension allows you to embed Mermaid graphs in your documents, including general flowcharts, sequence diagrams, gantt diagrams and more.

It adds a directive to embed mermaid markup. For example:

.. mermaid::

    sequenceDiagram
      participant Alice
      participant Bob
      Alice->John: Hello John, how are you?
      loop Healthcheck
          John->John: Fight against hypochondria
      end
      Note right of John: Rational thoughts <br/>prevail...
      John-->Alice: Great!
      John->Bob: How about you?
      Bob-->John: Jolly good!

By default, the HTML builder will simply render this as a div tag with class="mermaid", injecting the external javascript, css and initialization code to make mermaid works.

For other builders (or if mermaid_output_format config variable is set differently), the extension will use mermaid-cli to render as to a PNG or SVG image, and then used in the proper code.

sequenceDiagram
  participant Alice
  participant Bob
  Alice->John: Hello John, how are you?
  loop Healthcheck
      John->John: Fight against hypochondria
  end
  Note right of John: Rational thoughts <br/>prevail...
  John-->Alice: Great!
  John->Bob: How about you?
  Bob-->John: Jolly good!

You can also embed external mermaid files, by giving the file name as an argument to the directive and no additional content:

.. mermaid:: path/to/mermaid-gantt-code.mmd

As for all file references in Sphinx, if the filename is not absolute, it is taken as relative to the source directory.

In addition, you can use mermaid to automatically generate a diagram to show the class inheritance using the directive autoclasstree. It accepts one or more fully qualified names to a class or a module. In the case of a module, all the class found will be included.

Of course, these objects need to be importable to make its diagram.

If an optional attribute :full: is given, it will show the complete hierarchy of each class.

The option :namespace: <value> limits to the base classes that belongs to this namespace. Meanwhile, the flag :strict: only process the classes that are strictly defined in the given module (ignoring classes imported from other modules).

For example:

.. autoclasstree:: sphinx.util.DownloadFiles sphinx.errors.ExtensionError
    :full:

.. autoclasstree:: sphinx.util.DownloadFiles sphinx.errors.ExtensionError
   :full:

Or directly the module:

.. autoclasstree:: sphinx.util

.. autoclasstree:: sphinx.util

Installation

You can install it using pip

pip install sphinxcontrib-mermaid

Then add sphinxcontrib.mermaid in extensions list of your project's conf.py:

extensions = [..., "sphinxcontrib.mermaid"]

Directive options

sphinxcontrib-mermaid mermaid diagrams can be configured by rst/md frontmatter:

.. mermaid::
   :name: test

   <diagram>

```mermaid
---
name: test
---
<diagram>
  • name: determines the image's name for HTML output. NOTE: mermaid will use this as the id of the generated svg element, which can be useful for styling with custom css: #mydiagram > svg { height: 1000px }
  • alt: determines the image's alternate text for HTML output. If not given, the alternate text defaults to the mermaid code.
  • align: determines the image's position. Valid options are 'left', 'center', 'right'
  • caption: can be used to give a caption to the diagram.
  • zoom: can be used to enable zooming the diagram. For a global config see mermaid_d3_zoom below.
A preview after adding :zoom: option only to the first diagram example above:
  • fullscreen: can be used to enable fullscreen modal viewing of the diagram. For a global config see mermaid_fullscreen below.
  • config: JSON to pass through to the mermaid configuration. NOTE: The mermaid documentation uses YAML, but we must use JSON because Markdown processing of frontmatter will interfere.
  • title: Title to pass through to the mermaid configuration

Translations

For translated diagrams, store Mermaid source in an external .mmd file and provide localized files using Sphinx's figure_language_filename convention. For example, diagram.mmd and diagram.de.mmd can be referenced by the same directive, and Sphinx selects the file matching the active language.

Mermaid captions are included in gettext catalogs and translated like other figure captions. Inline Mermaid source is not extracted as prose; use localized external files when diagram labels need translation.

Config values

mermaid_output_format

The output format for Mermaid when building HTML files. This must be either 'raw' 'png' or 'svg'; the default is 'raw'. mermaid-cli is required if it's not raw

mermaid_cmd

The command name with which to invoke mermaid-cli program. The default is 'mmdc'; you may need to set this to a full path if it's not in the executable search path. If a string is specified, it is split using shlex.split to support multi-word commands. To avoid splitting, a list of strings can be specified. Examples:

mermaid_cmd = "npx mmdc"
mermeid_cmd = ["npx", "--no-install", "mmdc"]

mermaid_cmd_shell

When set to true, the shell=True argument will be passed the process execution command. This allows commands other than binary executables to be executed on Windows. The default is false.

mermaid_params

For individual parameters, a list of parameters can be added. Refer to Examples:

mermaid_params = ["--theme", "forest", "--width", "600", "--backgroundColor", "transparent"]

This will render the mermaid diagram with theme forest, 600px width and transparent background.

mermaid_sequence_config

Allows overriding the sequence diagram configuration. It could be useful to increase the width between actors. It needs to be a json file Check options in the documentation

mermaid_verbose

Use the verbose mode when call mermaid-cli, and show its output in the building process.

mermaid_pdfcrop

If using latex output, it might be useful to crop the pdf just to the needed space. For this, pdfcrop can be used. State binary name to use this extra function.

mermaid_init_config

Optional override of arguments to mermaid.initialize(), passed in as a JSON. Defaults to { "startOnLoad": True}.

mermaid_config

Optional default for each Mermaid directive's config frontmatter. Set it to a dictionary in conf.py:

mermaid_config = {
    "theme": "base",
    "themeVariables": {"primaryColor": "#BB2528"},
}

A directive's :config: option replaces this default for that diagram.

mermaid_dark_theme

The mermaid theme to use when dark mode is detected. Defaults to "dark". Valid values are any mermaid theme: "default", "neutral", "dark", "forest", "base".

mermaid_light_theme

The mermaid theme to use when light mode is detected. Defaults to "default". Valid values are the same as for mermaid_dark_theme.

For a theme that works well in both dark and light mode, set both to "neutral":

mermaid_dark_theme = "neutral"
mermaid_light_theme = "neutral"

mermaid_version

The version of mermaid that will be used to parse raw output in HTML files. This should match a version available on https://www.jsdelivr.com/package/npm/mermaid. The default is "11.12.1".

mermaid_use_local

Optional location of a local copy of mermaid.esm.min.mjs. By default, we will pull from jsdelivr.

The value can be either an absolute URL or a path relative to html_static_path (e.g. vendor/mermaid.esm.min.mjs if the file is vendored at _static/vendor/mermaid.esm.min.mjs). The same applies to the other *_use_local options below.

mermaid_include_elk

Whether to download and load the ELK JavaScript extensions. Defaults to False.

mermaid_include_zenuml

Whether to download and load the ZenuML JavaScript extensions. Defaults to False.

mermaid_elk_version

The version of mermaid ELK renderer that will be used. The default is "0.2.0".

mermaid_zenuml_version

The version of mermaid ZenuML renderer that will be used. The default is "0.2.2".

mermaid_elk_use_local

Optional location of a local copy of mermaid-layout-elk.esm.min.mjs. See mermaid_use_local for accepted values.

mermaid_zenuml_use_local

Optional location of a local copy of mermaid-zenuml.esm.min.mjs. See mermaid_use_local for accepted values.

mermaid_icon_packs

Optional mapping of icon-pack names to Iconify JSON URLs. Packs are registered lazily and fetched only when Mermaid uses an icon from them. Relative paths are resolved from html_static_path. This option applies to raw HTML output only.

For example:

mermaid_icon_packs = {
    "logos": "https://cdn.jsdelivr.net/npm/@iconify-json/logos@1/icons.json",
}

Icons from the pack can then be referenced with the registered name, such as logos:aws-lambda in an architecture diagram.

d3_use_local

Optional location of a local copy of d3.min.js. See mermaid_use_local for accepted values.

d3_version

The version of d3 that will be used to provide zoom functionality on mermaid graphs. The default is "7.9.0".

mermaid_d3_zoom

Enables zooming in all the generated Mermaid diagrams.

mermaid_width

Sets the default diagram width within its container. Default to 100%.

mermaid_height

Sets the default diagram height within its container. Default to 500px.

mermaid_fullscreen

Enables fullscreen modal viewing for all Mermaid diagrams. When enabled, a fullscreen button appears in the top-right corner of each diagram. Clicking it opens the diagram in a fullscreen modal overlay. The modal can be closed by pressing ESC, clicking outside the diagram, or clicking the close button. This feature is theme-agnostic and works with any Sphinx theme.

mermaid_fullscreen_button

Customizes the fullscreen button icon/text. Default is "⛶". You can use any Unicode character or emoji, for example "🔍" or "⛶".

mermaid_fullscreen_button_opacity

Customizes the fullscreen button opacity, to avoid fully obscuring important chart content. Default is 50 (percent). You can use any value from 0 to 100. Button becomes fully opaque on hover.

Markdown support

You can include Mermaid diagrams in your Markdown documents in Sphinx. You just need to setup the markdown support in Sphinx via myst-parser . See a minimal configuration from the tests.

Then in your .md documents include a code block as in reStructuredTexts:

```{mermaid}

    sequenceDiagram
      participant Alice
      participant Bob
      Alice->John: Hello John, how are you?
```

For GitHub cross-support, you can omit the curly braces and configure myst to use the mermaid code block as a myst directive. For example, in `conf.py`:

myst_fence_as_directive = ["mermaid"]

Building PDFs on readthedocs.io

In order to have Mermaid diagrams build properly in PDFs generated on readthedocs.io, you will need a few extra configurations.

  1. In your .readthedocs.yaml file (which should be in the root of your repository) include a post-install command to the Mermaid CLI:
        build:
          os: ubuntu-20.04
          tools:
            python: "3.8"
            nodejs: "16"
          jobs:
            post_install:
              - npm install -g @mermaid-js/mermaid-cli

Note that if you previously did not have a .readthedocs.yaml file, you will also need to specify all targets you wish to build and other basic configuration options. A minimal example of a complete file is:

# .readthedocs.yaml
# Read the Docs configuration file
# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
# Required
version: 2
# Set the version of Python and other tools you might need
build:
  os: ubuntu-24.04
  apt_packages:
    - libasound2t64
  tools:
    python: "3.11"
    nodejs: "20"
  jobs:
    post_install:
      - npm install -g @mermaid-js/mermaid-cli
# Build documentation in the docs/ directory with Sphinx
sphinx:
   configuration: docs/conf.py
# If using Sphinx, optionally build your docs in additional formats such as PDF
formats:
  - epub
  - pdf
python:
   install:
   - requirements: docs/requirements.txt
  1. In your documentation directory add file puppeteer-config.json with contents: :
{
 "args": ["--no-sandbox"]
}
  1. In your documentation conf.py file, add: :
mermaid_params = ["-p", "puppeteer-config.json"]