Introduction

YAML, TOML, and JSON are the three most popular formats for configuration files and data serialization. Each has different strengths and trade-offs. This guide compares them head-to-head so you can choose the right format for your project.

The Same Config in All Three Formats

YAML

# YAML - indentation-based
server:
  host: localhost
  port: 8080
  ssl:
    enabled: true
    cert: /path/to/cert.pem

database:
  host: db.example.com
  port: 5432
  name: myapp

features:
  - auth
  - logging
  - caching

TOML

# TOML - section-based
[server]
host = "localhost"
port = 8080

[server.ssl]
enabled = true
cert = "/path/to/cert.pem"

[database]
host = "db.example.com"
port = 5432
name = "myapp"

features = ["auth", "logging", "caching"]

JSON

{
  "server": {
    "host": "localhost",
    "port": 8080,
    "ssl": {
      "enabled": true,
      "cert": "/path/to/cert.pem"
    }
  },
  "database": {
    "host": "db.example.com",
    "port": 5432,
    "name": "myapp"
  },
  "features": ["auth", "logging", "caching"]
}

Feature Comparison

Feature	YAML	TOML	JSON
Comments	Yes (#)	Yes (#)	No
Trailing commas	N/A	No	No
Multiline strings	Yes	Yes	No
Explicit types	Implicit	Explicit	Explicit
Anchors/refs	Yes	No	No
Multiple docs	Yes (---)	No	No
Parsing speed	Slow	Medium	Fast
Universal support	Good	Growing	Everywhere

When to Use Each Format

Use YAML When

Writing Kubernetes manifests, CI/CD configs, or Docker Compose files
You need anchors and references to avoid repetition
Your team is already familiar with YAML (DevOps ecosystem)

Use TOML When

Writing Cargo.toml (Rust) or pyproject.toml (Python)
You want explicit types and unambiguous parsing
Simple, flat configuration with clear sections

Use JSON When

Building APIs, data exchange, or inter-service communication
You need maximum compatibility across all languages and platforms
Performance matters (JSON parsing is the fastest)

Key Takeaways

YAML is the most feature-rich but also the most complex and error-prone
TOML is the simplest and most explicit, ideal for straightforward configs
JSON is universal and fast but lacks comments and is harder to write by hand
Choose based on your use case: YAML for DevOps, TOML for Rust/Python, JSON for APIs
All three can represent the same data — the difference is ergonomics, not capability

Related Resources

TOML Validator YAML to JSON JSON Validator TOML Guide

YAML vs TOML vs JSON: Which Config Format Should You Use?