Frequently Asked Questions

My project isn’t building with autodoc

First, you should check out the Builds tab of your project. That records all of the build attempts that RTD has made to build your project. If you see ImportError messages for custom Python modules, you should enable the virtualenv feature in the Admin page of your project, which will install your project into a virtualenv, and allow you to specify a requirements.txt file for your project.

If you are still seeing errors because of C library dependencies, please see the below section about that.

How do I change my slug (the URL your docs are served at)?

We don’t support allowing folks to change the slug for their project. You can update the name which is shown on the site, but not the actual URL that documentation is served.

The main reason for this is that all existing URLs to the content will break. You can delete and re-create the project with the proper name to get a new slug, but you really shouldn’t do this if you have existing inbound links, as it breaks the internet.

How do I change behavior for Read the Docs?

When RTD builds your project, it sets the READTHEDOCS environment variable to the string True. So within your Sphinx file, you can vary the behavior based on this. For example:

import os
on_rtd = os.environ.get('READTHEDOCS') == 'True'
if on_rtd:
    html_theme = 'default'
    html_theme = 'nature'

The READTHEDOCS variable is also available in the Sphinx build environment, and will be set to True when building on RTD:

{% endif %}

I get import errors on libraries that depend on C modules


Another use case for this is when you have a module with a C extension.

This happens because our build system doesn’t have the dependencies for building your project. This happens with things like libevent and mysql, and other python things that depend on C libraries. We can’t support installing random C binaries on our system, so there is another way to fix these imports.

You can mock out the imports for these modules in your with the following snippet:

import sys
from unittest.mock import MagicMock

class Mock(MagicMock):
    def __getattr__(cls, name):
            return MagicMock()

MOCK_MODULES = ['pygtk', 'gtk', 'gobject', 'argparse', 'numpy', 'pandas']
sys.modules.update((mod_name, Mock()) for mod_name in MOCK_MODULES)

Of course, replacing MOCK_MODULES with the modules that you want to mock out.


The library unittest.mock was introduced on python 3.3. On earlier versions install the mock library from PyPI with (ie pip install mock) and replace the above import:

from mock import Mock as MagicMock

If such libraries are installed via, you also will need to remove all the C-dependent libraries from your install_requires in the RTD environment.

Client Error 401 when building documentation

If you did not install the test_data fixture during the installation instructions, you will get the following error:

slumber.exceptions.HttpClientError: Client Error 401: http://localhost:8000/api/v1/version/

This is because the API admin user does not exist, and so cannot authenticate. You can fix this by loading the test_data:

./ loaddata test_data

If you’d prefer not to install the test data, you’ll need to provide a database account for the builder to use. You can provide these credentials by editing the following settings:


Deleting a stale or broken build environment

If you’re having trouble getting your version to build, try wiping out the existing build/environment files. On your version list page /projects/[project]/versions there is a “Wipe” button that will remove all of the files associated with your documentation build, but not the documentation itself.

How do I host multiple projects on one CNAME?

We support the concept of Subprojects. If you add a subproject to a project, that documentation will also be served under the parent project’s subdomain.

For example, Kombu is a subproject of celery, so you can access it on the domain:

This also works the same for CNAMEs:

You can add subprojects in the Admin section for your project.

Where do I need to put my docs for RTD to find it?

Read the Docs will crawl your project looking for a Where it finds the, it will run sphinx-build in that directory. So as long as you only have one set of sphinx documentation in your project, it should Just Work.

I want to use the Blue/Default Sphinx theme

We think that our theme is badass, and better than the default for many reasons. Some people don’t like change though :), so there is a hack that will let you keep using the default theme. If you set the html_style variable in your, it should default to using the default theme. The value of this doesn’t matter, and can be set to /default.css for default behavior.

I want to use the Read the Docs theme locally

There is a repository for that: Simply follow the instructions in the README.

Image scaling doesn’t work in my documentation

Image scaling in docutils depends on PIL. PIL is installed in the system that RTD runs on. However, if you are using the virtualenv building option, you will likely need to include PIL in your requirements for your project.

I want comments in my docs

RTD doesn’t have explicit support for this. That said, a tool like Disqus (and the sphinxcontrib-disqus plugin) can be used for this purpose on RTD.

How do I support multiple languages of documentation?

See the section on Localization of Documentation.

Does Read The Docs work well with “legible” docstrings?

Yes. One criticism of Sphinx is that its annotated docstrings are too dense and difficult for humans to read. In response, many projects have adopted customized docstring styles that are simultaneously informative and legible. The NumPy and Google styles are two popular docstring formats. Fortunately, the default Read The Docs theme handles both formats just fine, provided your specifies an appropriate Sphinx extension that knows how to convert your customized docstrings. Two such extensions are numpydoc and napoleon. Only napoleon is able to handle both docstring formats. Its default output more closely matches the format of standard Sphinx annotations, and as a result, it tends to look a bit better with the default theme.

Can I document a python package that is not at the root of my repository?

Yes. The most convenient way to access a python package for example via Sphinx’s autoapi in your documentation is to use the Install your project inside a virtualenv using `` install`` option in the admin panel of your project. However this assumes that your is in the root of your repository.

If you want to place your package in a different directory or have multiple python packages in the same project, then create a pip requirements file. You can specify the relative path to your package inside the file. For example you want to keep your python package in the src/python directory, then create a requirements.readthedocs.txt file with the following contents:


Please note that the path must be relative to the file. So the example path above would work if the file is in the root of your repository. If you want to put the requirements in a file called requirements/readthedocs.txt, the contents would look like:


After adding the file to your repository, go to the Advanced Settings in your project’s admin panel and add the name of the file to the Requirements file field.

What commit of Read the Docs is in production?

We deploy from the rel branch in our GitHub repository. You can see the latest commits that have been deployed by looking on GitHub: