The design goals for YAML:

- YAML is easily readable by humans.
- YAML data is portable between programming languages.
- YAML matches the native data structures of agile languages.
- YAML has a consistent model to support generic tools.
- YAML supports one-pass processing.
- YAML is expressive and extensible.
- YAML is easy to implement and use.

Awesome YAML (Ain't Markup Language)

A collection of Awesome YAML (Ain't Markup Language) goodies for structured (meta) data in text.

Contributions welcome. Anything missing? Send in a pull request. Thanks.

Formats

"Standard" YAML

YAML HQ

• yaml.org - official YAML website by Clark C. Evans
  • YAML Spec v1.2 - 3rd edition, Oct 2009
  • YAML Quick Reference Card - one-page cheat sheet

"Safe" YAML, "Strict" YAML

• strictyaml - a type-safe YAML parser that parses and validates a restricted subset of the YAML specification
  • YAML Features Removed
    • NO Implicit Typing
    • NO Direct representations of objects
    • NO Duplicate Keys Disallowed
    • NO Explicit tags
    • NO Node anchors and refs
    • NO Flow style

Nested Text - YAML Simplified, YAML Evolved

"Safer" YAML - YAML Redux

• nestedtext.org, (github) - a human friendly data format similar to YAML but without the complexity and risk of YAML

Example:

# Contact information for our officers

president:
    name: Katheryn McDaniel
    address:
        > 138 Almond Street
        > Topeka, Kansas 20697
    phone:
        cell: 1-210-555-5297
        home: 1-210-555-8470
            # Katheryn prefers that we always call her on her cell phone.
    email: [email protected]
    additional roles:
        - board member

Articles

• YAML Quick Reference (Cheat Sheet) for Jekyll Data Files, Front Matter and Collections, Planet Jekyll
• Learn YAML in Y Minutes, Learn X in Y minutes series,
• Deep dive into TOML, JSON and YAML, Go Hugo HQ, Dec 2016
• YAML @ Wikipedia

Tips & Gotchas

Strings with Colons (:)

When to use quotes for your strings?

If your string includes a colon (:) followed by a space you MUST quote your string. Otherwise, the colon is interpreted as a key/value separator (e.g. key: value). Example:

title: "Text Processing with Ruby: Extract Value from the Data That Surrounds You"
title: "Sinatra: Up and Running - Ruby for the Web, Simply"
title: "Using JRuby: Bringing Ruby to Java"

Note: You can quote your strings using double quotes ("") e.g. "Using JRuby: Bringing Ruby to Java" or single quotes('') e.g. 'Using JRuby: Bringing Ruby to Java'.

No Tabs (\t) for Indentation - Use Spaces, Period

Note: Always use spaces for indentation, period. Make sure no tabs (\t) have somehow ended up in your datafile leading to unexpected results.

Predefined Boolean 'n' No Value Constants - True/False, Yes/No, On/Off, ~/Null

Note: The boolean true and false constants e.g.:

true, True, TRUE
y, Y, yes, YES, YES
on, ON, ON
false, False, FALSE
n, N, no, No, NO
off, Off, OFF

will become boolean values e.g. true or false. If you want end-up with a string e.g.:

recommend: Yes       # note: will become => true (boolean)

make sure you use a quoted version e.g.:

recommend: "Yes"     # note: will become => "Yes" (string)

Note: The same holds for the no value null constants e.g.:

~
null, Null, NULL

will become => null (no value). Note: A key without a value will end-up with a null value (and not an empty string, for example). To get an empty string use "" e.g.:

key1:           # note: value will become => null (no value); same as key1: null  or key1: ~
key2: ""        # note: value will become => "" (string)

JSON

JSON is (a subset of) YAML, that is YAML is JSON but JSON is NOT YAML ;-)

Example: Use the inline style for lists (that is, JSON arrays) and hashes (that is, JSON objects) for an alternative "JSON-style" syntax:

[
  { "title": "football.db - Open Football Data",
    "url":   "https://github.com/openfootball" 
  },
  { "title": "beer.db - Open Beer, Brewery 'n' Brewpub Data",
    "url":   "https://github.com/openbeer" 
  }
]

is the same as:

- title : football.db - Open Football Data
  url   : https://github.com/openfootball
- title : beer.db - Open Beer, Brewery 'n' Brewpub Data
  url   : https://github.com/openbeer

Tools & Services

• YAML Linter @ yamllint.com - online YAML validator / checker
• YAML Validator @ Code Beautify - online YAML validator / checker
• YAML Comparator @ yamline - online YAML comparator
• Yamlinc - compose multiple files using $include tag / compiler
• dasel ("data-selector") - Query and update data structures using selectors from the command line. Comparable to jq / yq but supports JSON, YAML, TOML and XML with zero runtime dependencies.

No Body Wants To Write YAML

No:
  Body:
    Wants:
      To:
        Write:
          - YAML

• noyaml.com, (github) - a rant about the state of devops tooling / the infrastructure sector

Mandatory "No Body Wants To Write YAML" reading list:

• Today we’re going to look at some general problems with the YAML format
• We replaced 1,000 lines of YAML with 10 structs and people started contributing again
• What if you used the same language and tools you use to define your app to define your infrastructure?
• A YAML file is almost always still 'valid' even if it is trunca
• The bug was that the YAML parser ignored the negative signs ... so negative GPS coordinates became positive ones
• Every YAML parser is a custom YAML parser
• There are 63 different ways to write multi-line strings in YAML

Misc

• Feed.TXT - web feed format with meta data in YAML
• YAML @ Stackoverflow - frequently asked questions (and answers) about YAML

Meta

License

The awesome list is dedicated to the public domain. Use it as you please with no restrictions whatsoever.

Questions? Comments?

Post them to the wwwmake forum. Thanks!