JSON vs XML vs YAML: Which Format Should You Use?

Quick Comparison Table

Here's the TL;DR version:

JSON: The Web Standard

Here's the same data in JSON:

{
  "person": {
    "name": "Alice",
    "age": 28,
    "email": "alice@example.com",
    "roles": ["admin", "editor"]
  }
}

Pros

• Native to JavaScript (no parsing surprises)
• Compact and lightweight
• Fast to parse in any language
• The de facto standard for REST APIs
• Every programming language has built in support

Cons

• No comments allowed
• No native date type (you use strings)
• Strict syntax can be annoying (trailing commas, double quotes)
• No support for references or anchors

Best for

REST APIs, web applications, JavaScript projects, data interchange between services. Basically anything on the web.

XML: The Enterprise Choice

Here's the same data in XML:

<?xml version="1.0" encoding="UTF-8"?>
<person>
  <name>Alice</name>
  <age>28</age>
  <email>alice@example.com</email>
  <roles>
    <role>admin</role>
    <role>editor</role>
  </roles>
</person>

Notice how much more typing that is? That's the XML tradeoff. You get more structure, but at the cost of verbosity.

Pros

• Supports attributes on elements
• Has namespaces for avoiding conflicts
• Schema validation with XSD
• Can include comments
• Mature ecosystem with XSLT, XPath, XQuery

Cons

• Verbose (lots of repeated tags)
• Larger file sizes
• Slower to parse
• More complex to work with programmatically
• Feels dated for modern web development

Best for

SOAP APIs (legacy enterprise systems), document markup, configuration in Java applications, situations where you need strict schema validation, RSS feeds.

YAML: The Config Favorite

Here's the same data in YAML:

person:
  name: Alice
  age: 28
  email: alice@example.com
  roles:
    - admin
    - editor

Look at how clean that is. No brackets, no quotes (usually), just indentation. This is why YAML is popular for config files.

Pros

• Most readable of the three
• Supports comments
• Smallest file sizes
• Multi document files (useful for Kubernetes)
• Anchors and aliases for reusing content

Cons

• Indentation is significant (tabs vs spaces issues)
• Some surprising behaviors (Norway problem: NO becomes false)
• Multiple ways to write the same thing
• Not ideal for data interchange (use JSON)
• Slower to parse than JSON

Best for

Config files (Docker Compose, Kubernetes, GitHub Actions, CI/CD pipelines), human edited files, documentation with embedded data.

When to Use Each One

Choose JSON when:

• Building a REST API
• Sending data between services
• Working with JavaScript/TypeScript
• You need fast parsing
• The data will be machine generated and machine consumed

Choose XML when:

• Working with legacy enterprise systems
• You need document markup (like HTML)
• Schema validation is critical
• You need attributes on elements
• The industry standard requires it (banking, healthcare)

Choose YAML when:

• Writing configuration files
• Humans will read and edit the file frequently
• You need comments in your data
• Working with DevOps tools (Ansible, Kubernetes, Docker)
• File size matters and data is relatively simple

The practical reality

Most developers use all three depending on context. Your API probably returns JSON, your Docker setup uses YAML, and that old integration with the bank uses XML. That's fine. Use the right tool for the job.

Converting Between Formats

Need to convert between these formats? It's usually straightforward since they all represent similar data structures.

Online tools

There are plenty of converters online. Just search for "JSON to YAML converter" or similar. Be careful with sensitive data though.

Command line

Tools like yq (YAML processor) and jq (JSON processor) can convert between formats:

# YAML to JSON
yq -o=json input.yaml > output.json

# JSON to YAML
yq -P input.json > output.yaml

In code

Most languages have libraries for all three formats:

// JavaScript
const yaml = require('js-yaml');
const jsonData = JSON.parse(jsonString);
const yamlString = yaml.dump(jsonData);

# Python
import json
import yaml

data = json.loads(json_string)
yaml_string = yaml.dump(data)