JSON vs TOML for Configuration

Quick answer: TOML is designed for human-edited configuration — it has comments, native dates, and a flat, INI-like readability. JSON is designed for data interchange — universal, strict, and machine-friendly, but awkward for config (no comments, easy to mis-nest). Use TOML for app/config files people edit by hand; use JSON for APIs and data passed between programs. To validate or reshape the JSON side, use the JSON Validator.

JSON optimizes for machines exchanging data. TOML optimizes for people writing config. That difference shows up immediately:

{
  "title": "My App",
  "owner": { "name": "Ada", "joined": "2026-01-01" },
  "database": { "ports": [8000, 8001], "enabled": true }
}

# TOML — note the comments and sections
title = "My App"

[owner]
name = "Ada"
joined = 2026-01-01   # a real date, not a string

[database]
ports = [8000, 8001]
enabled = true

TOML's [section] headers and key = value lines stay readable as nesting grows, where JSON's braces pile up. TOML also has a first-class date type; JSON has to encode dates as strings — see Dates in JSON.

Use TOML when the file is edited by humans and benefits from comments and clear sections — Cargo.toml, pyproject.toml, app settings. Its readability is the whole point.

Use JSON when programs exchange the data, a browser is involved, or you need the broadest possible tooling. JSON is native to JavaScript and supported everywhere, which TOML can't match.

TOML can get awkward for deeply nested or array-of-table structures, where JSON's explicit braces are actually clearer. So very nested config sometimes reads better as JSON (or YAML).

Most TOML libraries map cleanly to and from JSON-like structures, so you can author in TOML and emit JSON for a program to consume. After converting to JSON, check it with the JSON Validator and tidy it with the JSON Formatter. For the comments-in-JSON middle ground, see JSON5 vs JSONC; for the YAML comparison, JSON vs YAML.

Is TOML better than JSON for config? For human-edited config, usually yes — TOML has comments, native dates, and stays readable. For data interchange between programs, JSON is better because it's universal and machine-oriented.

Can TOML have comments? Yes, with #. This is a major reason it's preferred over JSON for configuration files, since plain JSON forbids comments.

Does TOML support dates natively? Yes — TOML has first-class date and date-time types. JSON has no date type, so dates are stored as ISO 8601 strings.

Can I convert TOML to JSON? Yes. TOML maps to the same basic structures as JSON (tables → objects, arrays → arrays), so libraries convert between them readily — useful for authoring in TOML but serving JSON.