Commenting in YAML

YAML (YAML Ain’t Markup Language) is a human-readable serialization format commonly used for configuration files and data exchange. One of the essential features of any programming or markup language is the ability to add comments, which are ignored by the parser but provide valuable information to humans reading the code. In this tutorial, we will explore how commenting works in YAML.

Inline Comments

YAML supports inline comments, which start with the number sign (#) and continue until the end of the line. Here is an example:

key: value  # This is an inline comment

In this example, everything after the # symbol on the same line is considered a comment and will be ignored by the YAML parser.

Block Comments

Unlike some other languages, YAML does not natively support block comments that can span multiple lines. However, you can achieve similar functionality in several ways:

1. Multiple Inline Comments: You can use multiple inline comments to create a block of commented text.

# This is the first line of a comment block
# This is the second line
# And this is the third

2. Using Editors or IDEs: Many text editors and Integrated Development Environments (IDEs) provide shortcuts for commenting out blocks of code, including YAML files. For example, in Sublime Text or Visual Studio Code, you can select a block of text and use Cmd + / on Mac or Ctrl + / on Linux and Windows to comment it out.

3. Using Vim: If you are using Vim, there are several ways to comment out blocks of code:

   • Comment all lines: :%s/^/#
   • Comment lines 10-15: :10,15s/^/#
   • Comment line 10 to current line: :10,.s/^/#
   • Comment line 10 to end: :10,$s/^/#
   • Using visual block mode, you can select a column of text and then press r followed by # to replace the selection with comment characters.

4. Alternative Approach: If your application allows additional fields in its YAML configuration that do not interfere with its functionality, you can use these fields for comments. This approach involves adding a field like "Description" or "Comment" at any level of your YAML structure and using it to hold your comments.

Description: >
  This is a comment block
  that spans multiple lines.

This method not only allows for block commenting but also makes the comments part of the data structure, potentially allowing them to be processed or displayed by applications that understand these additional fields.

Best Practices

• Use Comments Judiciously: Comments should enhance understanding without cluttering your YAML files. Use them to explain why certain configurations are chosen or what non-obvious parts of the configuration do.
• Keep Comments Up-to-Date: Ensure that comments reflect the current state of the configuration. Outdated comments can be misleading and decrease the maintainability of your configuration files.

In conclusion, while YAML does not support traditional block comments like some other languages, there are effective ways to achieve similar functionality through inline comments, editor features, or creative use of the data structure itself. By understanding these methods and using them appropriately, you can make your YAML configurations more readable and maintainable.