JSON vs TOML: Configuration Format Comparison

JSON vs TOML Overview

JSON and TOML are both popular data formats, but TOML (Tom's Obvious Minimal Language) was specifically designed for configuration files with a focus on human readability.

Quick Comparison

| Feature | JSON | TOML |

|---------|------|------|

| Syntax | Curly braces | INI-like |

| Comments | No | Yes |

| Readability | Good | Excellent |

| File Extension | .json | .toml |

| Parsing Speed | Faster | Moderate |

| Adoption | Universal | Growing |

Syntax Examples

JSON Configuration

{
  "database": {
    "server": "192.168.1.1",
    "ports": [8001, 8002, 8003],
    "connection_max": 5000,
    "enabled": true
  },
  "servers": {
    "alpha": {
      "ip": "10.0.0.1",
      "dc": "eqdc10"
    },
    "beta": {
      "ip": "10.0.0.2",
      "dc": "eqdc10"
    }
  }
}

TOML Configuration

# Database configuration
[database]
server = "192.168.1.1"
ports = [8001, 8002, 8003]
connection_max = 5000
enabled = true

# Server configurations
[servers.alpha]
ip = "10.0.0.1"
dc = "eqdc10"

[servers.beta]
ip = "10.0.0.2"
dc = "eqdc10"

Key Differences

Comments

JSON: No native comment support

{
  "_comment": "Using workaround for comments",
  "setting": "value"
}

TOML: Full comment support

# This is a proper comment
setting = "value"  # Inline comment also works

Readability

TOML eliminates visual clutter:

• No curly braces or quotes for keys
• Clear section headers
• Natural table syntax
• Better for nested structures

Data Types

Both support:

• Strings, integers, floats, booleans
• Arrays
• Nested structures

TOML additions:

• Dates and times (native)
• Inline tables

# TOML native date-time
created = 2026-02-14T10:30:00Z

# Inline table
point = { x = 1, y = 2 }

When to Use JSON

Web APIs - Industry standard

Data interchange - Universal support

JavaScript - Native parsing

Performance - Faster parsing

Tooling - More validators and formatters

When to Use TOML

Configuration files - More readable

Rust projects - Cargo.toml standard

Python packaging - pyproject.toml

Human editing - Easier to maintain

Comments needed - Documentation in config

Conversion Examples

TOML to JSON (Python)

import json
import tomli  # Python 3.11+ has tomllib built-in

with open('config.toml', 'rb') as f:
    data = tomli.load(f)

with open('config.json', 'w') as f:
    json.dump(data, f, indent=2)

JSON to TOML (Python)

import json
import tomli_w

with open('config.json') as f:
    data = json.load(f)

with open('config.toml', 'wb') as f:
    tomli_w.dump(data, f)

Common Use Cases

JSON Strengths

{
  "api_response": {
    "status": 200,
    "data": [
      {"id": 1, "name": "Item 1"},
      {"id": 2, "name": "Item 2"}
    ]
  }
}

TOML Strengths

# Application configuration
[app]
name = "MyApp"
version = "1.0.0"
debug = false

[app.database]
url = "postgresql://localhost/mydb"
pool_size = 10

[app.logging]
level = "info"
file = "/var/log/myapp.log"

Common Pitfalls

TOML Tables Order

# Wrong - can't add to [fruit] after array
[fruit]
name = "apple"

[[fruit.varieties]]  # Array of tables
name = "red"

[fruit]  # Error! Already defined
color = "red"

# Correct - define all table keys first
[fruit]
name = "apple"
color = "red"

[[fruit.varieties]]
name = "red"

TOML String Escaping

# Basic strings (escapes processed)
path = "C:\\Users\\name"

# Literal strings (raw)
regex = '<\i\c\s>'

# Multi-line strings
description = """
Line 1
Line 2
Line 3"""

Decision Guide

Choose JSON when:

• Building web APIs
• Need maximum compatibility
• Performance is critical
• Working with JavaScript/browsers
• Generating data programmatically

Choose TOML when:

• Writing configuration files
• Human readability is priority
• Comments are essential
• Working with Rust or Python projects
• Config needs version control review

Popular Tools

JSON Tools

• jq (command-line processor)
• Every programming language
• Online formatters everywhere

TOML Tools

• tomli/tomllib (Python)
• toml crate (Rust)
• TOML Language Support (VS Code)
• Online TOML validators

Ecosystem Adoption

JSON: Universal (1999+)

• All web browsers
• Every major language
• REST API standard

TOML: Growing (2013+)

• Rust: Cargo.toml
• Python: pyproject.toml
• Hugo static site generator
• Many CLI tools

Conclusion

JSON dominates data interchange and APIs, while TOML excels at configuration files. Many modern projects use both: JSON for runtime data and TOML for human-editable config. Choose based on your use case—if humans will frequently edit it, TOML's readability wins; if machines generate it, JSON's universality is unbeatable.