JSON vs XML vs YAML

Learning Focus

Choose the right serialisation format by understanding the trade-offs between JSON, XML, and YAML.

Same Data, Three Formats

data.json

{
  "user": {
    "id": 101,
    "name": "Alice",
    "roles": ["admin", "editor"],
    "active": true
  }
}

data.xml

<user>
  <id>101</id>
  <name>Alice</name>
  <roles>
    <role>admin</role>
    <role>editor</role>
  </roles>
  <active>true</active>
</user>

data.yaml

user:
  id: 101
  name: Alice
  roles:
    - admin
    - editor
  active: true

Feature Comparison

Feature	JSON	XML	YAML
Comments	✗	✓	✓
Native data types	Partial	✗ all strings	✓ incl. dates
Human readability	High	Medium	Very High
Parse speed	Very Fast	Slower	Slowest
Schema / Validation	JSON Schema	XSD, DTD	Various
Whitespace sensitive	No	No	Yes
Primary use	Web APIs, storage	Documents, SOAP	Config, CI/CD

Decision Flowchart

Format Decision Guide

• Need comments or human editing?
  • Yes, and it's a config or CI/CD file → YAML (Docker Compose, Kubernetes, GitHub Actions)
  • Yes, and it's a legacy enterprise system → XML (SOAP, Java/Spring)
  • No → JSON (Web APIs, programmatic storage)

Concept Map

Concept Flow

Data Serialisation
  ├── JSON  → Web APIs and Databases
  ├── XML   → Enterprise Documents
  └── YAML  → Config and DevOps

Common Pitfalls

Pitfall	Consequence	Prevention
Using YAML for large payloads	Slow parsing, indentation bugs	Use JSON for machine-to-machine transfer
Using JSON for Kubernetes manifests	Verbose, no comments	Use YAML as intended by the ecosystem
YAML boolean coercion: yes, no, on, off	Coerce to bool unexpectedly	Quote values if you mean the string
XML for REST APIs	Heavy, slow, verbose	Default to JSON unless legacy requires XML

What's Next

• Previous: History and Design — Review the JSON origin story.
• Next: JSON Syntax Overview — Master the six JSON syntax rules.
• Section Overview — Return to the Introduction module index.