Is YAML a Superset of JSON?

What "Superset" Means

If YAML is a superset of JSON, then:

• Every valid JSON document is valid YAML
• YAML parsers can read JSON files directly
• JSON syntax works inside YAML files
• YAML has additional features JSON doesn't

Proof: JSON Works in YAML Parsers

This JSON:

{
  "name": "John",
  "age": 30,
  "hobbies": ["reading", "gaming"]
}

Is valid YAML (paste it directly):

# This is valid YAML!
{"name": "John", "age": 30, "hobbies": ["reading", "gaming"]}

Python proof:

import yaml
import json

json_string = '{"name": "John", "age": 30}'

# Both produce the same result
json_result = json.loads(json_string)
yaml_result = yaml.safe_load(json_string)

print(json_result == yaml_result)  # True!

Edge Cases and YAML Versions

YAML 1.1 Gotchas

# YAML 1.1 might interpret these differently:
yes: true       # "yes" becomes boolean true
no: false       # "no" becomes boolean false
on: true        # "on" becomes boolean true
off: false      # "off" becomes boolean false

# In JSON these would be string keys:
{"yes": "value"} → key is the STRING "yes"

# YAML 1.2 fixed this - now matches JSON behavior

Mixing JSON and YAML Syntax

Since JSON is valid YAML, you can mix both styles in one file:

# YAML style with JSON inline
name: John Doe
age: 30

# JSON-style inline arrays (valid YAML!)
hobbies: ["reading", "gaming", "hiking"]

# JSON-style inline objects
address: {"city": "NYC", "zip": "10001"}

# YAML-style same data
address_yaml:
  city: NYC
  zip: "10001"

When to Use Each Style

• YAML style: Better for long, nested configs
• JSON inline: Better for short arrays/objects
• Mixed: Common in real-world configs