Last modified: January 24, 2026

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YAML

YAML, or "YAML Ain't Markup Language," is a human-readable data serialization format. It is commonly used for configuration files and data exchange between languages with different data structures. YAML is designed to be readable and concise, with a focus on data readability over markup verbosity.

Basics of YAML

  1. Data Types: YAML supports scalar types (such as strings, integers, and floats), complex mappings (associative arrays or objects), and sequences (lists or arrays).

  2. Syntax: YAML syntax is designed to be easily readable and writable by humans. It uses indentation to denote structure, allowing for a more natural representation of nested data structures.

YAML Syntax Rules

  1. Indentation-based Hierarchy: Indentation is used to represent the hierarchy and structure of data. The amount of indentation affects the interpretation of the data.
  2. Scalars: Scalars are simple, single-value data types, including integers, floats, and strings.
  3. Mappings: Mappings (similar to dictionaries or objects in other languages) are represented using a colon and space : to denote key-value pairs.
  4. Lists: Lists (or sequences) are denoted by a hyphen - at the start of the item in the list.
  5. Support for Comments: YAML supports comments using the # symbol.

Example

Here's a simple example:

employee:
  name: John Doe
  age: 30
  department: Engineering
  address:
    street: 1234 Main St
    city: Anytown
    state: CA
    zipCode: 12345
  skills:
    - Java
    - C#
    - Python

Benefits of YAML

  1. Human-Friendly: YAML is designed with human readability in mind, making it easy to write and understand.
  2. Flexible: Capable of representing complex data structures in a clear manner.
  3. Widespread Usage: Commonly used in configuration files and development tools.

Common Uses of YAML

YAML vs JSON

While both YAML and JSON are used for data serialization, YAML is more human-readable, which makes it preferred for configuration files. JSON, being more compact and parsed natively by JavaScript, is often used for web APIs and data interchange.

Feature YAML (YAML Ain't Markup Language) JSON (JavaScript Object Notation)
Format Human-readable, text-based format. Lightweight, text-based format.
Readability Highly readable due to its minimalistic design and use of indentation. Readable, though less human-friendly than YAML due to bracket usage.
Data Types Supports complex data types and structures. Supports basic data types like string, number, array, boolean, and null.
Comments Allows comments. Does not support comments.
Hierarchical Structure Uses indentation to denote structure, which can be more intuitive. Uses braces { } and brackets [ ] to denote objects and arrays.
Parsing Requires a YAML parser. Easily parsed with standard JavaScript functions.
File Extension .yaml or .yml .json
Verbose Less verbose than JSON in many cases due to the lack of brackets. More verbose due to use of brackets and commas.
Security Requires careful parsing due to potential security issues. Generally secure, but also requires secure parsing practices.
Use Cases Often used for configuration files, data serialization, and in applications where human readability is a priority. Commonly used in web services, APIs, and settings where a lightweight and easily parsable format is desired.

Best Practices for YAML

  1. Consistent Indentation: Maintain consistent indentation for readability and to avoid errors.
  2. Use Comments Wisely: Use comments to explain complex parts of the YAML file.
  3. Avoid Excessive Nesting: Over-nesting can make YAML files complex and hard to read.
  4. Validate Your YAML: Use a YAML validator to ensure your syntax is correct.
  5. Be Aware of Data Types: YAML is sensitive to data types; be mindful of strings vs. integers and other data type distinctions.