What’s the Deal with YAML? A Comprehensive Definition and Explanation

YAML, short for “YAML Ain’t Markup Language,” is a human-readable data serialization format widely used in the IT industry and software development. Statistics show that approximately 69% of developers use YAML in some way, and about 3.8% of repositories on GitHub contain YAML files. Unlike other data serialization formats such as JSON and XML, YAML’s main focus is on simplicity and ease of use. It was first introduced in 2001 and is widely adopted in configuration files, data exchange between languages with different data structures, and applications that require a human-readable format.

“YAML: A human-readable data serialization format that takes its syntax from real-world examples.” – Ingy döt Net, one of the creators of YAML

What is YAML? Definition of YAML Ain’t Markup Language

YAML is a superset of JSON, meaning that every JSON file is also a valid YAML file, but YAML offers additional features that JSON lacks. Some key differences between JSON and YAML include using indentation for nesting in YAML, while JSON relies on brackets and curly braces. The elements in a YAML file can be key-value pairs, arrays, or nested arrays.

ℹ️ Synonyms: data serialization language, human-readable data format, YAML Ain’t Markup Language

How it Works

A YAML file contains a series of data elements, each defined by a combination of indentation and succinct syntax. The indentation shows the nesting of the data, while the syntax determines how values are represented and separated. YAML utilizes several major data types: scalars (strings, numbers, booleans), sequences (lists), and mappings (key-value pairs).

An example of a simple YAML file:

  name: John Doe
  age: 30
    - photography
    - hiking
    - reading

In this example, “person” is a mapping containing two key-value pairs (“name” and “age”) and a sequence (“hobbies”). Formatting these elements with YAML’s simple and intuitive syntax helps promote readability for both developers and non-developers.

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Benefits of using YAML

  • Human-readable: YAML’s intuitive syntax promotes readability and understanding, making it easier for people to work with the data it represents.
  • Flexible and extensible: YAML supports various data structures, including mappings, sequences, and scalars, allowing for customization and adaptation to varying use cases.
  • Language-agnostic: YAML can be used with many programming languages, providing a consistent way of representing data structures and sharing data between different languages and frameworks.
  • Portable: As a plain-text format, YAML does not depend on any specific application or system, making it easy to use across different platforms and devices.
  • Wide adoption: Many popular infrastructure as code frameworks, such as Ansible, Kubernetes, and Docker Compose, use YAML as their primary configuration language, making YAML a key skill for modern IT professionals.

YAML Use Cases

YAML is utilized in a variety of settings across the software development landscape:

Configuration files

Many software applications and services use YAML files as their primary configuration format due to its human-readable nature, which makes it easier for developers and system administrators to understand and manage these configurations.

Data exchange

Since YAML is language-agnostic, it is often used for sharing data between systems built using different programming languages. The consistent way of representing data provided by YAML simplifies cross-language data exchange.

Infrastructure as code

YAML’s simplicity and wide adoption in the DevOps ecosystem make it ideal for infrastructure as code (IaC) tools like Ansible, Kubernetes, and Docker. In these tools, YAML serves as the standard way to define declarative configurations that describe the target state of infrastructure components.

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Best Practices

When working with YAML, it is crucial to follow best practices to ensure maintainability, readability, and compatibility of your YAML files. Always use consistent and meaningful indentation to accurately represent data hierarchy. Limit line lengths to enhance readability and include comments to provide context or explain specific configuration choices. Leverage code validation tools, like linters, to identify syntax errors and adhering to proper style guidelines. Additionally, consider using version control systems like Git to track changes and facilitate collaboration between team members.

Most Recommended Books about YAML

To deepen your understanding of YAML, the following books are highly recommended:

1. Mastering Ansible by Jesse Keating – While focused on Ansible, this book also covers YAML basics and best practices for writing Ansible playbooks.
2. YAML Essentials by Fabrizio Ferri – This book provides a hands-on guide to using YAML for various applications, ranging from configuration files to data storage and transformations.
3. Efficient Data Exchange with YAML by Simon St. Laurent – Geared towards professional programmers, this book goes beyond YAML basics and explores how YAML can simplify data exchange between programming languages.


YAML is a versatile and human-readable data serialization format that has become an essential tool for developers and IT professionals alike. Its simplicity makes it easy to use, and its wide adoption in the software development ecosystem ensures it remains a valuable skill to have. By mastering YAML best practices and understanding its use cases, you can enhance your ability to work with configuration files, infrastructure as code tools, and data exchange between different languages and frameworks.

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Back in 2013, I founded Echo with the simple business idea: "Connect great tech companies around the globe with the brightest software engineers in Eastern Europe." We've employed hundreds of talents so far and keep going.
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li-url Lou Reverchuk

IT Entrepreneur

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