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YAML (YAML Ain’t Markup Language) is a data serialization language (a fancy way of saying that YAML formats data for storage or transmission) that is often used to create configuration files. Jekyll uses YAML (sometimes in combination with Liquid) for formatting. YAML files have the extension .yml.

Basic formatting

YAML is designed to be human-readable. It does not use any kind of angle brackets that are commonly used as markup tags. Instead, it uses blank spaces to form structures. Because of this, YAML is very particular about the placement of spaces. An extra space somewhere can easily make your file invalid.

Two most common types of elements in YAML are mappings and lists. You will see both of these in a Jeykll site.

  • Mapping is a simple key-value pair:

    key: value
  • A list is a sequence of items. Each item starts with two spaces (or a tab in some editors) of indent and a hyphen. For example:

      - name: monocyte
      - name: macrophage
      - name: neutrophil

Note: Because “tab” is not implemented the same way across editors, it’s best to just type two spaces. With that said, in GitHub “tab” equates two spaces.

YAML in Jekyll websites

In Jeykll, YAML is seen mostly within _config.yml file and the “front matter” of any page.


_config.yml contains site-wide configuration options. The main items that needs to be customized in the LSP templates are outlined on the Customization page.

For extra information and technical references on _config.yml file content, please refer to Jekyll’s documentation on configuration.

Front Matter

Front matter tells Jekyll how to process and build each page.

  • Front matter must be the first thing in the file
  • Front matter must take form of valid YAML set between triple dashed lines.
  • As an advanced option, within front matter, you can set predefined variables or create your own.
    • These variables will then be available through Liquid tags within the same file or in any layouts or includes the current page/post relies on.

An example of front matter would be:

layout: page
title: Example # will display as the page name on the left navigation bar
permalink: example # defines page URL
published: true
nav_exclude: false # toggle to true to exclude this page from naviation bar
has_children: false # toggle to true if this page has subpages
parent: Motivation # defines this page as a subpage of the page titled "Motivation"

Read more about controlling page navigation structure on your site in Just the Docs .

Homepage hero banner

A key styling component in the LSP templates is the hero banner on the homepage. The formatting for hero banner is located in the front matter of the homepage Markdown file

Detailed instructions can be found under Customization.