Documentation style guide


Where possible, text should be written in UK English. However, discretion and common sense can both be applied. For example, where text refers to code elements that exist in US English, the spelling of these elements should not be changed to UK English.

Try to be concise and to the point in your writing. It is acceptable to link to official documentation elsewhere rather than repeating content. It’s also good practice not to assume that your reader has the same level of knowledge as you, so if you’re covering a new or complicated topic, then providing contextual links to help the reader is encouraged.

Feel free to include a “Further reading” section at the end of a page if you have additional resources an interested reader might find helpful.


In reStructuredText, headings are denoted using symbols to underline the text. The headings used across the documentation use the following hierarchy, which is borrowed from the Python style guide:

  • #####: Top level header (reserved for the main index page)

  • *****: Title header (used once at the top of a new page)

  • =====: Section headers

  • -----: Subsection headers

  • ^^^^^: Sub-subsection headers

  • """"": Paragraphs

The length of the underline must be at least as long as the title itself.

Ensure that you do not skip header levels when creating your document structure, i.e., that a section is followed by a subsection, and not a sub-subsection.

Line length

Please keep the line lengths to a maximum of 79 characters. This ensures that the pages and tables do not get so wide that side scrolling is required.

Blank spaces at the ends of lines must also be removed, otherwise the tox build checks will fail (it will warn you about trailing whitespace).

Anchor labels

Adding an anchor label at the top of the page allows for the page to be referenced by other pages. For example for the FAQ page this would be:

.. _faq:


When the reference is used in a document, the displayed text will be that of the next heading immediately following the label (so, FAQ in this example), unless specifically overridden.

If you use labels within a page to refer, for example, to a subsection, use a label that follows the format: [pagelabel]-[Section] e.g., for this “Anchor labels” section, something like _docs-Anchor: or _docs-Label:. Using a consistent style will aid greatly when referencing from other pages.


It is generally best to avoid screenshots where possible. If you need to refer to text output, you can use code blocks. For diagrams, we recommend the use of Mermaid.

Code blocks

Our documentation uses the Sphinx extension “sphinx-copybutton”, which creates a small button on the right-hand side of code blocks for users to copy the code snippets we provide.

The copied code will strip out the prompt symbol ($) so that users can paste commands directly into their terminal. For user convenience, please ensure that code output is presented in a separate code block to the commands.

Vertical whitespace

One newline between each section helps ensure readability of the documentation source code.

Common words

There are some common words that should follow specific usage in text:

  • cloud-init: Always hyphenated, and follows sentence case, so only capitalised at the start of a sentence.

  • metadata, datasource: One word.

  • user data, vendor data: Two words, not to be combined or hyphenated.

When referring to file names, which may be hyphenated, they should be decorated with backticks to ensure monospace font is used to distinguish them from regular text.


Acronyms are always capitalised (e.g., JSON, YAML, QEMU, LXD) in text.

The first time an acronym is used on a page, it is best practice to introduce it by showing the expanded name followed by the acronym in parentheses. E.g., Quick EMUlator (QEMU). If the acronym is very common, or you provide a link to a documentation page that provides such details, you will not need to do this.