Frequently asked questions

Building and publishing your project

Why does my project have status “failing”?

Projects have the status “failing” because something in the build process has failed. This can be because the project is not correctly configured, because the contents of the Git repository cannot be built, or in the most rare cases because a system that Read the Docs connects to is not working.

First, you should check out the Builds tab of your project. By clicking on the failing step, you will be able to see details that can lead to resolutions to your build error.

If the solution is not self-evident, you can use an important word or message from the error to search for a solution.

Why does my project have status “passed” but I get a 404 page?

This often happens because you don’t have an index.html file being generated.

Make sure you have one of the following files at the top level of your documentation source:

  • index.rst (Sphinx)

  • (MkDocs or Sphinx with MyST)


To test if your docs actually built correctly, you can navigate to a specific page that you know is part of the documentation build, for example /en/latest/README.html.

Why do I get import errors from libraries depending on C modules?


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

This happens because the build system does not have the dependencies for building your project, such as C libraries needed by some Python packages (e.g. libevent or mysql). For libraries that cannot be installed via apt in the builder there is another way to successfully build the documentation despite missing dependencies.

With Sphinx you can use the built-in autodoc_mock_imports for mocking. 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.

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.

You can specify an exact path to your documentation using a Read the Docs Configuration file.

How can I avoid search results having a deprecated version of my docs?

If readers search something related to your docs in Google, it will probably return the most relevant version of your documentation. It may happen that this version is already deprecated and you want to stop Google indexing it as a result, and start suggesting the latest (or newer) one.

To accomplish this, you can add a robots.txt file to your documentation’s root so it ends up served at the root URL of your project (for example, We have documented how to set this up in robots.txt support.

How do I change the version slug of my project?

We don’t support allowing folks to change the slug for their versions. But you can rename the branch/tag to achieve this. If that isn’t enough, you can request the change sending an email to

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:

We also keep an up-to-date changelog.

Additional features and configuration

How do I add additional software dependencies for my documentation?

For most Python dependencies, you can can specify a requirements file which details your dependencies. You can also set your project documentation to install your Python project itself as a dependency.

See also

Build process overview

An overview of the build process.

How to create reproducible builds

General information about adding dependencies and best-practices for maintaining them.

Build process customization

How to customize your builds, for example if you need to build with different tools from Sphinx or if you need to add additional packages for the Ubuntu-based builder.

Configuration file v2

Reference for the main configuration file, readthedocs.yaml


Reference for adding Debian packages with apt for the Ubuntu-based builders

Other FAQ entries

Can I have access to additional features or settings?

If this is just a dependency issue, see How do I add additional software dependencies for my documentation?.

Read the Docs offers some settings (feature flags) which can be used for a variety of purposes. To enable these settings, please send an email to and we will change the settings for the project.

See also

Feature flags

Reference of all Feature Flags that can be requested.

How do I change behavior when building with 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 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.

Can I remove advertising from my documentation?

Yes. See Opting out of advertising.

How do I change my project 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.

If that isn’t enough, you can request the change sending an email to

Big projects

How do I host multiple projects on one custom domain?

We support the concept of subprojects, which allows multiple projects to share a single domain. If you add a subproject to a project, that documentation will be served under the parent project’s subdomain or custom domain.

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

This also works the same for custom domains:

You can add subprojects in the project admin dashboard.

For details on custom domains, see our documentation on Custom domains.

How do I support multiple languages of documentation?

Read the Docs supports multiple languages. See the section on Localization of documentation.


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

Read the Docs automatically applies the sphinx-rtd-theme to projects that do not have a defined theme. If you build a Sphinx project locally, you should specify that you are using sphinx-rtd-theme.

See also

sphinx-rtd-theme documentation

See the official documentation for instructions to enable it in your Sphinx theme.

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.


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.txt file with the following contents:


Please note that the path must be relative to the working directory where pip is launched, rather than the directory where the requirements file is located. Therefore, even if you want to move the requirements file to a requirements/ directory, the example path above would work.

You can customize the path to your requirements file and any other installed dependency using a Read the Docs Configuration file.

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.


To use these extensions you need to specify the dependencies on your project by following this guide.

I need to install a package in a environment with pinned versions

To ensure proper installation of a Python package, the pip install method will automatically upgrade every dependency to its most recent version in case they aren’t:term:pinned by the package definition. If instead you’d like to pin your dependencies outside the package, you can add this line to your requirements or environment file (if you are using Conda).

In your requirements.txt file:

# path to the directory containing relative to the project root
-e .

In your Conda environment file (environment.yml):

# path to the directory containing relative to the environment file
-e ..

Can I use Anaconda Project and anaconda-project.yml?

Yes. With anaconda-project>=0.8.4 you can use the Anaconda Project configuration file anaconda-project.yaml (or anaconda-project.yml) directly in place of a Conda environment file by using dependencies: as an alias for packages:.

I.e., your anaconda-project.yaml file can be used as a conda.environment config in the .readthedocs.yaml config file if it contains:

  - python=3.9
  - scipy

Other documentation frameworks

How can I deploy Jupyter Book projects on Read the Docs?

According to its own documentation,

Jupyter Book is an open source project for building beautiful, publication-quality books and documents from computational material.

Even though Jupyter Book leverages Sphinx “for almost everything that it does”, it purposedly hides Sphinx files from the user, and instead generates them on the fly from its declarative _config.yml. As a result, you need to follow some extra steps to make Jupyter Book work on Read the Docs.

As described in the official documentation, you can manually convert your Jupyter Book project to Sphinx with the following configuration:

         # Generate the Sphinx configuration for this Jupyter Book so it builds.
         - "jupyter-book config sphinx docs/"