YAML vs JSON: Complete Comparison Guide []

What is JSON?

JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format. It uses key-value pairs enclosed in curly braces {} and ordered lists in square brackets []. JSON is language-independent, easy to parse programmatically, and the standard format for web APIs and data storage.

JSON was formally specified in RFC 8259 (Internet Standard) and ECMA-404. It supports six data types: objects, arrays, strings, numbers, booleans (true/false), and null. The official MIME type is application/json. Need to convert JSON to YAML? Try our free online converter or see our Python, JavaScript, or Java guides.

What is YAML?

YAML (YAML Ain't Markup Language) is a human-readable data serialization language that uses indentation instead of brackets to define structure. It supports comments (using #), multi-line strings, and complex data types. YAML is commonly used for configuration files in Docker, Kubernetes, Ansible, and CI/CD pipelines like GitHub Actions.

The current version is YAML 1.2 (released October 2021), which was specifically designed to be a superset of JSON. This means every valid JSON document is also valid YAML. YAML represents data using three primitives: scalars (strings, numbers), sequences (arrays), and mappings (objects). YAML is commonly used for Kubernetes manifest configuration, Docker Compose files, and Helm charts.

YAML vs JSON: Key Differences

Here's a detailed comparison of the key differences between YAML and JSON:

When to Use YAML

Choose YAML when your use case prioritizes human readability and editing:

• Configuration files – Docker Compose, Kubernetes manifests, Ansible playbooks, and similar infrastructure tools use YAML because developers need to read and edit these files frequently.
• CI/CD pipelines – GitHub Actions, GitLab CI, CircleCI, and Azure Pipelines use YAML for workflow definitions due to its clean, readable syntax.
• Human-editable files – When non-developers or DevOps engineers need to modify configuration without specialized tools.
• Files requiring comments – YAML's comment support makes it ideal for documenting configuration options inline.
• Complex hierarchical data – YAML's indentation clearly shows nested relationships without bracket clutter.
• API specifications – OpenAPI/Swagger definitions are often written in YAML for readability, though they also support JSON.

When to Use JSON

Choose JSON when speed, compatibility, and machine processing are priorities:

• Web APIs and REST services – JSON is the de facto standard for API responses. Nearly all web APIs return JSON data.
• Data exchange between systems – JSON's widespread support across programming languages makes it ideal for interoperability.
• JavaScript/browser applications – JSON parses natively in JavaScript with JSON.parse(), making it the natural choice for web apps.
• Performance-critical applications – JSON's simpler syntax means faster parsing and serialization than YAML.
• Database storage – NoSQL databases like MongoDB and PostgreSQL's JSONB type use JSON for document storage.
• Machine-generated configuration – When files are primarily generated and consumed by programs, not humans.

YAML vs JSON Performance

JSON is faster than YAML for both parsing and serialization. Here's why:

Why JSON is Faster

• Simpler syntax – JSON's explicit brackets and braces require less complex parsing logic than YAML's indentation rules.
• No type inference – JSON has strict typing (strings must be quoted), while YAML parsers must infer types from context.
• Native browser support – JavaScript engines have optimized JSON parsers built in.
• Fewer features to process – YAML's anchors, aliases, and custom types add parsing overhead.

When Performance Matters

For most use cases, the performance difference is negligible. YAML's slower parsing only becomes significant when:

• Processing thousands of files per second
• Parsing very large files (10+ MB)
• Building high-throughput API services

For configuration files loaded once at startup, use whichever format is more readable for your team.

Code Examples: Same Data in JSON vs YAML

Here's the same data structure represented in both formats:

JSON Example

{
  "name": "my-application",
  "version": "2.0.0",
  "description": "A sample web application",
  "author": {
    "name": "Developer Team",
    "email": "[email protected]"
  },
  "database": {
    "host": "localhost",
    "port": 5432,
    "name": "app_db",
    "ssl": true
  },
  "features": [
    "authentication",
    "api",
    "logging"
  ],
  "environments": {
    "development": {
      "debug": true,
      "log_level": "verbose"
    },
    "production": {
      "debug": false,
      "log_level": "error"
    }
  }
}

YAML Example

# Application configuration file
name: my-application
version: "2.0.0"
description: A sample web application

author:
  name: Developer Team
  email: [email protected]

# Database settings
database:
  host: localhost
  port: 5432
  name: app_db
  ssl: true

features:
  - authentication
  - api
  - logging

# Environment-specific settings
environments:
  development:
    debug: true
    log_level: verbose
  production:
    debug: false
    log_level: error