JSON vs YAML: Which Format Should You Use?

Choosing between JSON and YAML? This comprehensive comparison helps you decide which format is best for your project.

Quick Comparison

What is JSON?

JSON (JavaScript Object Notation) is a lightweight data format based on JavaScript object syntax. It uses curly braces, square brackets, and double quotes.

{
  "name": "jsoneditor.io",
  "version": "2.0",
  "features": ["format", "validate", "convert"],
  "free": true,
  "users": null
}

JSON Characteristics

• Strict syntax - Double quotes required, no trailing commas
• Limited data types - String, number, boolean, null, array, object
• No comments - Cannot add inline documentation
• Portable - Works everywhere JavaScript runs

What is YAML?

YAML (YAML Ain't Markup Language) is a human-readable data serialization format that uses indentation instead of brackets.

name: jsoneditor.io
version: "2.0"
features:
  - format
  - validate
  - convert
free: true
users: null  # No users tracked for privacy

YAML Characteristics

• Flexible syntax - Quotes optional for most strings
• Extended data types - Dates, timestamps, binary data
• Comments supported - Use # for inline documentation
• Indentation-based - Whitespace is significant

When to Use JSON

1. API Responses

JSON is the standard format for REST APIs. Every programming language has built-in or widely-available JSON parsers.

{
  "status": "success",
  "data": {
    "id": 123,
    "email": "user@example.com"
  }
}

2. Browser Applications

JavaScript can parse JSON natively with JSON.parse(). No external libraries needed.

const data = JSON.parse(response)

3. Data Storage

JSON is widely supported by databases (MongoDB, PostgreSQL JSONB, Elasticsearch).

4. When Performance Matters

JSON parsers are typically 2-10x faster than YAML parsers because the syntax is simpler.

5. Strict Validation Needed

JSON's strict syntax means fewer ambiguities. JSON Schema provides robust validation.

When to Use YAML

1. Configuration Files

YAML's readability makes it ideal for configs that humans edit frequently.

# Application configuration
server:
  host: localhost
  port: 3000

database:
  host: localhost
  port: 5432
  name: myapp

2. Kubernetes and Docker

The cloud-native ecosystem standardized on YAML for manifests and compose files.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-app
spec:
  replicas: 3

3. CI/CD Pipelines

GitHub Actions, GitLab CI, CircleCI, and Travis CI all use YAML.

name: Build and Test
on: [push]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - run: npm test

4. Documentation with Data

When you need to mix data with comments and explanations.

# User roles and permissions
roles:
  admin:
    # Full access to all resources
    permissions: ["read", "write", "delete", "admin"]
  user:
    # Standard user access
    permissions: ["read", "write"]

Detailed Comparison

Syntax Complexity

JSON has 6 rules to learn:

1. Objects use {}
2. Arrays use []
3. Strings use double quotes
4. No trailing commas
5. Keys must be quoted strings
6. No comments

YAML has more rules:

• Indentation matters (2 spaces recommended)
• Strings are usually unquoted
• Lists use - prefix
• Multiple document support with ---
• Anchors and aliases for reuse
• Various multi-line string formats

Error Potential

JSON errors are usually obvious:

• Missing comma
• Unclosed bracket
• Invalid escape sequence

YAML errors can be subtle:

• Wrong indentation level
• Tab vs space issues
• Unintended type coercion (yes becomes boolean true)

File Size

YAML is typically 15-30% smaller than equivalent JSON due to:

• No quotes around most strings
• No curly braces
• No square brackets for simple lists

JSON (87 characters):

{"servers":[{"host":"api.example.com","port":443}],"timeout":30}

YAML (71 characters):

servers:
  - host: api.example.com
    port: 443
timeout: 30

Parsing Performance

JSON parsing benchmarks (operations per second):

• JavaScript: ~500,000 ops/sec
• Python: ~50,000 ops/sec

YAML parsing benchmarks:

• JavaScript: ~50,000 ops/sec
• Python: ~5,000 ops/sec

JSON is roughly 10x faster to parse.

Common Pitfalls

YAML Boolean Gotcha

# These all become boolean true!
norway: NO   # Becomes false (country code issue)
french: FR   # String (no issue)

Solution: Quote values that might be misinterpreted.

JSON Number Precision

{
  "id": 9007199254740993
}

Large integers can lose precision in JavaScript. Use strings for IDs.

YAML Indentation Errors

server:
  host: localhost
   port: 3000  # Extra space causes error!

Always use consistent indentation (2 spaces recommended).

Converting Between Formats

Use jsoneditor.io to convert instantly:

1. Paste JSON or YAML
2. Click Convert
3. Select target format
4. Copy or download result

All conversion happens in your browser for privacy.

Recommendations

Summary

Choose JSON when:

• Building APIs
• Working in browsers
• Performance is critical
• You need strict validation

Choose YAML when:

• Writing configuration files
• Need human readability
• Want inline comments
• Working with Kubernetes/Docker

Both formats are excellent. The right choice depends on your use case. Use jsoneditor.io to work with both formats and convert between them instantly.