YAML Ain’t Markup Language (YAML™) version 1.2

Revision 1.2.2 (2021-10-01)

Copyright presently by YAML Language Development Team1
Copyright 2001-2009 by Oren Ben-Kiki, Clark Evans, Ingy döt Net

This document may be freely copied, provided it is not modified.

Status of this Document

This is the YAML specification v1.2.2. It defines the YAML 1.2 data language. There are no normative changes from the YAML specification v1.2. The primary objectives of this revision are to correct errors and add clarity.

This revision also strives to make the YAML language development process more open, more transparent and easier for people to contribute to. The input format is now Markdown instead of DocBook, and the images are made from plain text LaTeX files rather than proprietary drawing software. All the source content for the specification is publicly hosted2.

The previous YAML specification3 was published 12 years ago. In that time span, YAML’s popularity has grown significantly. Efforts are ongoing to improve the language and grow it to meet the needs and expectations of its users. While this revision of the specification makes no actual changes to YAML, it begins a process by which the language intends to evolve and stay modern.

The YAML specification is often seen as overly complicated for something which appears to be so simple. Even though YAML often is used for software configuration, it has always been and will continue to be a complete data serialization language. Future YAML plans are focused on making the language and ecosystem more powerful and reliable while simultaneously simplifying the development process for implementers.

While this revision of the specification is limiting itself to informational changes only, there is companion documentation intended to guide YAML framework implementers and YAML language users. This documentation can continue to evolve and expand continually between published revisions of this specification.

See:

Abstract

YAML™ (rhymes with “camel”) is a human-friendly, cross language, Unicode based data serialization language designed around the common native data types of dynamic programming languages. It is broadly useful for programming needs ranging from configuration files to internet messaging to object persistence to data auditing and visualization. Together with the Unicode standard for characters4, this specification provides all the information necessary to understand YAML version 1.2 and to create programs that process YAML information.

Contents

Chapter 1. Introduction to YAML

YAML (a recursive acronym for “YAML Ain’t Markup Language”) is a data serialization language designed to be human-friendly and work well with modern programming languages for common everyday tasks. This specification is both an introduction to the YAML language and the concepts supporting it. It is also a complete specification of the information needed to develop applications for processing YAML.

Open, interoperable and readily understandable tools have advanced computing immensely. YAML was designed from the start to be useful and friendly to people working with data. It uses Unicode printable characters, some of which provide structural information and the rest containing the data itself. YAML achieves a unique cleanness by minimizing the amount of structural characters and allowing the data to show itself in a natural and meaningful way. For example, indentation may be used for structure, colons separate key/value pairs and dashes are used to create “bulleted” lists.

There are many kinds of data structures, but they can all be adequately represented with three basic primitives: mappings (hashes/dictionaries), sequences (arrays/lists) and scalars (strings/numbers). YAML leverages these primitives and adds a simple typing system and