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Automatic C++ library API documentation generator using Doxygen, Sphinx, and Breathe. Exhale revives Doxygen's class / file hierarchies using reStructuredText for superior markup syntax / websites.

Project description

Exhale is a Sphinx extension that depends on the excellent Breathe extension which enables parsing Doxygen documentation into the Sphinx domain. Exhale provides a layer of automation, enabling launching Doxygen and generating the full website all from your Exhale will execute these actions by way of sphinx-build being invoked, allowing you to use it for hosting on Read the Docs. Exhale was designed for generating html output, and may not be appropriate for other builders provided by Sphinx.

See it in Action

The ExhaleCompanion repository has three builds to demonstrate the different options with respect to creating a Tree View, as well as details of specific HTML Theme choices:

HTML Theme Choice TreeView Created ExhaleCompanion Docs
RTD Theme Yes rtd-docs
Bootstrap Theme Yes bootstrap-docs
Alabaster No alabaster-docs


Exhale is a Sphinx Extension that depends on Breathe for access to the Doxygen reStructuredText directives, and both BeautifulSoup and lxml for parsing the generated Doxygen XML documentation. Exhale also uses six help account for the Python 2 unicode dilemma. The easiest way to install Exhale is:

# NOTE: see version compatibility notes below.
$ pip install exhale

This will install Exhale, as well as all of its dependencies.


If you fail pip install exhale and it is failing on lxml, you will likely need to install the proper development libraries. See the lxml installation instructions for possible fixes.

lxml is readily available for Read The Docs and generally installs seamlessly for Unix systems, but my understanding is Windows users may need to put a little more effort in to get it to install.

Exhale Version Compatibility with Python, Sphinx, and Breathe

Exhale Version Python Version Sphinx Version Breathe Version
0.2.1-0.2.3 2.7, 3.3+ >=1.6.1 “Any”
<=0.2.0 2.7, 3.3+ >=1.0 “Any”

Sphinx 2.0 requires Python 3.5+. Breathe 4.13.0 drops support for Sphinx<2.0 in better support of the Sphinx C++ domain.


  • Unless you have a genuine need for Python 2.7, you will be better served by pinning sphinx>=2.0 and breathe>=4.13.0. It has many important improvements.

  • For Python 3.5+, you should pin your documentation requirements to:

  • For Python 2.7, you should pin your documentation requirements to:


Order matters, namely that sphinx and breathe appear / are installed before exhale. Exhale 0.* releases will continue support Python 2.7, but users need to be aware of the dependencies between Python, Sphinx, and Breathe versions.


See the full documentation and usage guide.

Exhale might not be the tool you are looking for! It was designed to be as intuitive and flexible as possible, but it does require more machinery to get everything started.

Why use it?
You would use Exhale if you want to have beautiful Sphinx generated websites, but also see the value of the Class and File hierarchies provided by Doxygen. From running Doxygen for you, to organizing your full API every time, you won’t need to worry about your documentation getting out of sync with the code — it’s regenerated on the fly every time.
Why not use it?

It may be more involved than you need. Check out the breathe-apidoc tool that comes with your installation of breathe. It is quite similar to the Sphinx API doc tool, and that may be all you are looking for to get your documentation displayed.

If you are working with a small enough framework, you may also be satisfied with just using the .. autodoxygenindex:: directive from breathe. It works very well!

The Main Difference

The Class and File hierarchies are only available in Sphinx via Exhale 😊

Depending on the size and complexity of your project, breathe-apidoc or autodoxygenindex may be more appropriate.

Quickstart Guide

You will need to edit 2 files: to configure the extensions, and index.rst (or whatever document you choose) to include the generated api in a toctree directive.

Setup the Extensions in

Assuming your Doxygen documentation is in order, and you already have your Sphinx project ready to go, we need to configure the Breathe and Exhale extensions. For this guide I assume the following directory structure:

├── docs/
│   ├──
│   └── index.rst
├── include/
│   └── common.hpp
└── src/
    └── common.cpp

This structure is not required, but you’ll need to change values accordingly.


When using relative paths, these are always relative to In the above structure I do not have a “separate source and build directory” from Sphinx. If you do, make sure you are using the correct paths.

# The `extensions` list should already be in here from `sphinx-quickstart`
extensions = [
    # there may be others here already, e.g. 'sphinx.ext.mathjax'

# Setup the breathe extension
breathe_projects = {
    "My Project": "./doxyoutput/xml"
breathe_default_project = "My Project"

# Setup the exhale extension
exhale_args = {
    # These arguments are required
    "containmentFolder":     "./api",
    "rootFileName":          "library_root.rst",
    "rootFileTitle":         "Library API",
    "doxygenStripFromPath":  "..",
    # Suggested optional arguments
    "createTreeView":        True,
    # TIP: if using the sphinx-bootstrap-theme, you need
    # "treeViewIsBootstrap": True,
    "exhaleExecutesDoxygen": True,
    "exhaleDoxygenStdin":    "INPUT = ../include"

# Tell sphinx what the primary language being documented is.
primary_domain = 'cpp'

# Tell sphinx what the pygments highlight language should be.
highlight_language = 'cpp'

With the above settings, Exhale would produce the docs/api folder, the file docs/api/library_root.rst (among many others), and it would use Doxygen to parse docs/../include and save the output in docs/doxyoutput. Meaning the following structure would be created:

├── docs/
│   ├── api/
│   │   └── library_root.rst
│   │
│   ├──
│   ├── index.rst
│   │
│   └── doxyoutput/
│       └── xml/
│           └── index.xml
├── include/
│   └── common.hpp
└── src/
    └── common.cpp


You are by no means required to use Exhale to generate Doxygen. If you choose not to I assume you have the wherewithal to figure it out on your own.

Optional: Create a Proper Clean Target

The sphinx-quickstart utility will create a Makefile for you, you are advised to create an explicit clean target that removes the generated utilities.

  1. You can just as easily specify to breathe_projects a path such as _build/doxyoutput/xml, or ../build/doxyoutput/xml if you have separate source and build directories. This will ensure that a make clean will delete these.

    To avoid confusing users who are new to Sphinx, I encourage something in the same directory as for simplicity.

  2. The generated API must appear in the Sphinx source directory. If you put it under _build, it will not get parsed.

So bust out the Makefile provided by Sphinx Quickstart and add clean to the .PHONY line, and the clean target as shown below (assuming you’ve been using the paths specified above):

.PHONY: help Makefile clean

    rm -rf doxyoutput/ api/


make requires TAB characters! If you just copy-pasted that, you got space characters (sorry).


The above code must appear before the %: Makefile “catch-all” target that Sphinx produced by default. Otherwise…well the catch-all target catches all!


If you find a problem or think there is something that should change, please submit an issue (or pull request!) explaining what should change. I made this because it was something I really wanted, and felt the community at large could benefit from as well. I put a lot of effort into making it flexible, but it is by no means perfect.


This project could not exist without the already excellent tools available: Doxygen, Sphinx, Breathe, and many others. In particular, though, for the Tree View hierarchies to be successful, I vendor copies of two excellent libraries that I make no claims to. They are vendored with your installation of Exhale, in accordance with each project’s license:

  1. For non-bootstrap, I used Kate Morley’s excellent and lightweight collapsibleLists including the sample CSS / images on that post. She includes a generous CC0 1.0 license for these files, as well as the rest of her website.

    For every HTML Theme I have tried, except for ones using bootstrap, this library works reliably and consistently. It matches the Sphinx RTD theme quite well, too!

  2. For bootstrap, I used Jon Miles’ comprehensive bootstrap-treeview library. Jon Miles hosts this library using the Apache v2 license.

    This library is exceptionally well thought out and enables an impressive amount of customization. At this time, Exhale does not expose any of the available customizations. If there is a specific one you’d like to see, please join the discussion here.

Both of these libraries and copies of their licenses can be found in the data folder of the source code.


This project uses a BSD 3-clause license, in hopes that it will be accessible to most projects. If you require a different license, please raise an issue and I will consider a dual license.

The full license is available here.

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