JSON vs TOML — Config Format Comparison for Developers

JSON vs TOML: Choosing the Right Config Format

JSON vs TOML comparison: syntax, comments, dates, type support, and when to use TOML (Cargo.toml, pyproject.toml, Hugo) vs JSON (package.json, tsconfig.json).

TOML is designed for human-readable configuration with native support for comments, dates, and times. JSON is better for machine-generated config and API exchange. Rust uses TOML for Cargo.toml; Node.js uses JSON for package.json.

JSON vs TOML: Configuration Format Showdown

Both JSON and TOML are used as configuration file formats, but TOML was explicitly designed to fix JSON's limitations as a config language.

What TOML Adds Over JSON

Comments: TOML supports # comments. JSON does not.
Dates & Times: TOML has native datetime types. JSON treats dates as strings.
Tables: TOML uses [section] headers for structured grouping.
Array of Tables: [[array.of.tables]] for repeated configuration blocks.

Ecosystem Adoption

TOML: Rust (Cargo.toml), Python packaging (pyproject.toml), Hugo static site generator, GitLab CI.
JSON: Node.js (package.json), TypeScript (tsconfig.json), VS Code (settings.json), Composer (composer.json).

json

# Same config in JSON vs TOML

# JSON (no comments, verbose):
{
  "package": {
    "name": "my-app",
    "version": "1.0.0",
    "authors": ["Alice <alice@example.com>"]
  },
  "dependencies": {
    "serde": "1.0"
  }
}

# TOML (human-friendly with comments):
# Application metadata
[package]
name = "my-app"
version = "1.0.0"
authors = ["Alice <alice@example.com>"]

# Runtime dependencies
[dependencies]
serde = "1.0"

Frequently Asked Questions

Why does Rust use TOML instead of JSON for Cargo.toml?

TOML was chosen for Cargo because it supports comments (important for annotating dependencies), has cleaner human syntax, and handles dates natively.

Can I convert JSON to TOML?

Yes. Use our free JSON to TOML converter at json2x.com/tools/json-to-toml.

Is TOML valid JSON?

No. TOML and JSON are separate formats with incompatible syntax. TOML uses key = value and [section] headers; JSON uses { "key": value } braces.