Since many projects will need special features in their documentation, Sphinx is designed to be extensible on several levels.
This is what you can do in an extension: First, you can add new :term:`builder`s to support new output formats or actions on the parsed documents. Then, it is possible to register custom reStructuredText roles and directives, extending the markup. And finally, there are so-called "hook points" at strategic places throughout the build process, where an extension can register a hook and run specialized code.
An extension is simply a Python module. When an extension is loaded, Sphinx imports this module and executes its setup() function, which in turn notifies Sphinx of everything the extension offers -- see the extension tutorial for examples.
The configuration file itself can be treated as an extension if it contains a setup() function. All other extensions to load must be listed in the :confval:`extensions` configuration value.
Builtin Sphinx extensions
These extensions are built in and can be activated by respective entries in the :confval:`extensions` configuration value:
There are several extensions that are not (yet) maintained in the Sphinx distribution. The Wiki at BitBucket maintains a list of those.
If you write an extension that you think others will find useful, please write to the project mailing list (join here) and we'll find the proper way of including or hosting it for the public.
Where to put your own extensions?
Extensions local to a project should be put within the project's directory structure. Set Python's module search path, sys.path, accordingly so that Sphinx can find them. E.g., if your extension foo.py lies in the exts subdirectory of the project root, put into :file:`conf.py`:
import sys, os sys.path.append(os.path.abspath('exts')) extensions = ['foo']
You can also install extensions anywhere else on sys.path, e.g. in the site-packages directory.