JSON vs YAML: When to Use Each

A practical guide for developers choosing between JSON and YAML for configuration files, APIs, CI/CD pipelines, and data serialization.

When to Use JSON

1. REST APIs & Web Services

JSON is the de facto standard for REST APIs. Every programming language has built-in or well-supported JSON parsing libraries. The format is predictable, and validation is straightforward.

// API Response - JSON is perfect here
{
  "user": {
    "id": 12345,
    "name": "John Doe",
    "email": "john@example.com",
    "roles": ["admin", "editor"]
  },
  "timestamp": "2024-12-05T10:30:00Z"
}

Why JSON wins: Native browser support, fast parsing, universal compatibility, no whitespace ambiguity.

2. Configuration Files for JavaScript/Node.js

Files like package.json, tsconfig.json, and .eslintrc.jsonuse JSON because Node.js can require() them directly without external parsers.

3. Data Storage & NoSQL Databases

MongoDB, CouchDB, and many NoSQL databases use JSON-like formats (BSON) for document storage. JSON integrates seamlessly with these systems.

4. When Strict Schema Validation is Critical

JSON Schema provides robust validation. The strict syntax (quoted keys, no trailing commas) prevents many common configuration errors.

When to Use YAML

1. CI/CD Pipeline Configs

GitHub Actions, GitLab CI, CircleCI, and most CI/CD tools use YAML. The readable syntax makes complex workflows easier to understand and maintain.

# .github/workflows/deploy.yml - YAML is perfect here
name: Deploy Production
on:
  push:
    branches: [main]
jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Install dependencies
        run: npm install
      - name: Run tests
        run: npm test
      - name: Deploy
        run: npm run deploy
        env:
          API_KEY: ${{ secrets.API_KEY }}

Why YAML wins: No quote noise, comments for documentation, multi-line strings without escaping, cleaner for large configs.

2. Kubernetes & Docker Compose

Kubernetes manifests and Docker Compose files are YAML-first. The container orchestration community has standardized on YAML for its readability when defining complex infrastructure.

3. Application Configuration Files

For config files that humans edit frequently (database configs, feature flags, environment settings), YAML's readability reduces errors. Comments allow inline documentation.

# config.yml - Comments make this self-documenting
database:
  host: localhost
  port: 5432
  # Connection pool settings
  pool:
    min: 2
    max: 10
    idle_timeout: 30s  # Close idle connections after 30 seconds

4. Ansible Playbooks & Infrastructure as Code

Ansible, Terraform (partially), and configuration management tools prefer YAML for defining infrastructure because it's easier to read and write than JSON equivalents.

Syntax Comparison: Same Data, Both Formats

{
  "service": {
    "name": "api-gateway",
    "version": "2.1.0",
    "ports": [8080, 8443],
    "environment": {
      "LOG_LEVEL": "info",
      "MAX_CONNECTIONS": 100
    }
  }
}

service:
  name: api-gateway
  version: 2.1.0
  ports:
    - 8080
    - 8443
  environment:
    LOG_LEVEL: info
    MAX_CONNECTIONS: 100

Same information, ~40% fewer characters in YAML. For large configs, this difference is significant for readability.

Common Pitfalls

Conversion Between Formats

Need to switch between JSON and YAML? Our converter tools handle the transformation while preserving data integrity:

Decision Matrix

Best Practices

For JSON:

• Use 2 or 4 space indentation consistently
• Validate with JSON Schema before deployment
• Use .json file extension
• For comments, use documentation tools or README files
• Consider JSONC (JSON with Comments) for config files in VS Code projects

For YAML:

• Always use 2 spaces for indentation (never tabs)
• Quote strings that might be interpreted as booleans ("yes", "no")
• Use --- document separator for multi-document files
• Validate with tools like yamllint before committing
• Add comments explaining non-obvious configuration choices

Conclusion

Use JSON for APIs, data interchange, JavaScript-heavy projects, and scenarios requiring strict validation and fast parsing.

Use YAML for configuration files, CI/CD pipelines, infrastructure definitions, and situations where human readability and maintenance are priorities.

Many projects use both: YAML for configuration and CI/CD, JSON for API communication and data storage. Understanding the strengths of each format helps you make the right choice for each use case.