Standards for contributing to Yocto Project documentation

This document attemps to standardize the way the Yocto Project documentation is created.

It is currently a work in progress.

Text standards

Bulleted lists

Though Sphinx supports both the * and - characters for introducing bulleted lists, we have chosen to use only - for this purpose.

Though not strictly required by Sphinx, we have also chosen to use two space characters after - to introduce each list item:

-  Paragraph 1

-  Paragraph 2

As shown in the above example, there should also be an empty line between each list item.

An exception to this rule is when the list items are just made of a few words, instead of entire paragraphs:

-  Item 1
-  Item 2

This is again a matter of style, not syntax.

Line wrapping

Source code for the documentation shouldn't have lines wider than 80 characters. This makes patch lines more readable and code easier to quote in e-mail clients.

If you have to include long commands or lines in configuration files, provided the syntax makes this possible, split them into multiple lines, using the \ character.

Here is an example:

$ scripts/install-buildtools \
  --without-extended-buildtools \
  --base-url \
  --release yocto-4.0.1 \
  --installer-version 4.0.1

Exceptions are granted for file contents whose lines cannot be split without infringing syntactic rules or reducing readability, as well as for command output which should be kept unmodified.

Project names

Project names should be capitalized in the same way they are on Wikipedia, in particular:

  • BitBake
  • OpenEmbedded

There are exceptions in which such names can be used in lower case:

  • When referring to a package name
  • When referring to the corresponding command name
  • When used in a cross-reference title. Such titles are usually in lower case.

File, tool and command names

File, tool and command names should be double tick-quoted. For example, ``conf/local.conf`` is preferred over "conf/local.conf".


Every variable should be mentioned with:


This assumes that VARIABLE is described either in the Yocto Project documentation variable index (ref-manual/variables.rst) or in the BitBake User Manual (doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst)

If it is not described yet, the variable should be added to the glossary before or in the same patch it is used, so that :term: can be used.

ReStructured Text Syntax standards

This section has not been filled yet

Adding screenshots

The preferred format for adding screenshots is Portable Network Graphics (PNG). Compared to the JPEG format, PNG is lossless and compresses screenshots better.

Screenshots are stored in a figures/ subdirectory.

To include a screenshot in PNG format:

.. image:: figures/user-configuration.png
   :align: center

A diagram with many details usually needs to use the whole page width to be readable on all media. In this case, the :align: directive is unnecessary:

   :scale: 100%

Conversely, you may also shrink some images to to prevent them from filling the whole page width:

   :scale: 50%

For some types of screenshots, for example showing programs displaying photographs or playing video, the JPEG format may be more appropriate, because it is better at compressing real-life images:

.. image:: figures/vlc.jpg
   :align: center
   :scale: 75%

Adding new diagrams

New diagrams should be added in Scalable Vector Graphics (SVG) format. Thanks to this, diagrams render nicely at any zoom level on generated documentation, instead of being pixelated.

The recommended tool for creating SVG diagrams for the Yocto Project documentation is Inkscape.


The "GNOME HIG Colors" palette is used in our diagrams (get it from if you don't get it from Inkscape).

It's easier to use than the default one in Inkscape, as it has fewer but sufficient colors. This is a way to guarantee that we use consistent colors across the diagrams used in our documentation.

See for details about working with color palettes in Inkscape.

Template diagram

The template/ directory contains a template.svg file to make it easier to create diagrams. In particular, you can use it to copy standard text, shapes, arrows and clipart to the new SVG document.


The recommended font for description text and labels is Nimbus Roman, size 10. Labels are in bold.

template.svg contains ready-to-copy labels.

Text boxes

Text boxes are rectangle boxes, with rounded corners, and contain centered text or labels. Their stroke color is slightly darker than their fill color.

See template.svg for example boxes with different colors, which are ready to be reused.


Only Public Domain files are accepted for clipart. Openclipart is the best known and recommended source of such clipart.

It is also required to state the source of each new clipart in the commit log, to make it possible to check its origin.

For the sake of consistency across diagrams, we recommend to use existing cliparts, whenever possible.

If cliparts in template.svg do not satisfy your requirements, you can add to said file new cliparts, from e.g. Openclipart. Newly added cliparts shall stay consistent in style and color with existing ones.