YAML Quick Reference


YAML is a markup language that is designed to be easy to read, write and understand for humans as well as computers.

An advantage of using YAML is that the content defined with it is structured and directly usable in many programming languages. For example, it allows one to easily create mappings or sequences.

YAML is used in webgen for the configuration file, for specifying the meta information of a path in Webgen Page Format and some other places, too.


The complete syntax specification for YAML is rather hard to digest but provides useful information for corner cases.

The YAML Cookbook is much easier to read and provides information on all types (mappings, sequences, strings, numbers, …) that are available with YAML.

For a short reminder of the syntax, the YAML Reference Card is the go-to place.


  • Mappings from keys to values (used for specifying meta information) can either be specified in block or inline format:

    title: This is the page title
    in_menu: true
    mapping: {key: value, other key: other value}
  • Sequences of values also have a block and inline format:

    destination: [file_system, custom_out]
      - [/, file_system, src]
      - [/, file_system, /mnt/picture, '**/*.jpg']
  • Strings can be specified just by typing them. Note that when a string looks like some other data type (like a number), one has to quote it:

    simple: some string here
    'key with : colon': value here
    date as string: '2013-03-15'
  • Numbers (with or with fractions) are automatically recognized:

    amount: 100
    cost: 10.50
  • There are some ways to specify timestamps (see Timestamp Type for the full possibilities):

    created_at: 2013-03-15
    modified_at: 2013-03-19 20:10:23
  • Boolean values can also be specified:

    this is true: true
    this is false: false
  • Null values (i.e. the empty value) can be specified in two ways:

    key with null value: ~
    another key with null value: null