YAML Format Specification & Configuration Guide

YAML (YAML Ain't Markup Language) is a human-friendly data serialization standard for all programming languages. It is commonly used for configuration files and in applications where data is being stored or transmitted.

Introduction

YAML targets many of the same communications applications as Extensible Markup Language (XML) but has a minimal syntax which intentionally differs from XML. It uses Python-style indentation to indicate nesting, making it very readable.

Key Features

Human-Readable: Designed to be easily read by humans.
Concise: Minimal syntax compared to XML or JSON.
Expressive: Supports complex data structures like lists, associative arrays, and scalars.
Portable: Works across different programming languages.

Syntax

YAML uses indentation (spaces, not tabs) to represent structure.

Scalars

Strings, numbers, and booleans are written directly.

name: John Doe
age: 30
isStudent: false

Lists (Sequences)

Lists are denoted by a hyphen -.

fruits:
  - Apple
  - Banana
  - Orange

Dictionaries (Mappings)

Key-value pairs use a colon :.

address:
  street: 123 Main St
  city: Anytown

Example

invoice: 34843
date   : 2001-01-23
bill-to: &id001
  given  : Chris
  family : Dumars
  address:
    lines: |
      458 Walkman Dr.
      Suite #292
    city    : Royal Oak
    state   : MI
    postal  : 48046
ship-to: *id001
product:
  - sku         : BL394D
    quantity    : 4
    description : Basketball
    price       : 450.00

Use Cases

Configuration Management: Ansible, Kubernetes, Docker Compose all use YAML.
CI/CD Pipelines: GitHub Actions, GitLab CI use YAML for workflow definitions.
Data Serialization: Storing data in a readable format.