# Types of content source files¶

Jupyter Book supports many kinds of source files for your book’s content. These sections cover the major types of content, and how you can control their behavior in Jupyter Book. See the list of sections to the left for information about each type.

## Allowed content types¶

In general, these are the types of content supported in Jupyter Book (along with links to their section in this book):

Markdown files

These are text files written in either CommonMark or in MyST Markdown.

Jupyter Notebooks

AKA, .ipynb files. These files can contain markdown cells with MyST Markdown.

A Jupyter Notebook can utilise any program kernel that implements the Jupyter messaging protocol for executing code. There are kernels available for Python, Julia, Ruby, Haskell and many other languages.

MyST markdown notebooks

These are markdown files (ending in .md) that will be converted to a notebook and executed.

reStructuredText.

These are text files used by the Sphinx documentation engine (which is used by Jupyter Book). It is recommended to use MyST Markdown instead.

Custom Notebook Formats

Any other file type can be auto-converted before execution, by assigning it a custom Python function, for example those provided by the Jupytext conversion tool.

## Rules for all content types¶

There are a few things that are true for all content types. Here is a short list:

• Files must have a title. Generally this means that they must begin with a line that starts with a single #

• Use only one top-level header. Because each page must have a clear title, it must also only have one top-level header. You cannot have multiple headers with single # tags in them.

• Headers should increase linearly. If you’re inside of a section with one #, then the next section lower should start with ##. Avoid jumping straight from # to ###.

## Two-way conversion between text-files and .ipynb files¶

For information about how to convert between text files and .ipynb files for use with Jupyter Book, see Convert a Jupytext file into a MyST notebook.