TOML vs JSON: Which Config Format Should You Use?

Q: "What is the main difference between TOML and JSON?"

"TOML is designed to be written and read by humans, with comments, clean tables, and no brackets everywhere. JSON is a stricter data-interchange format optimized for machines, and it does not allow comments."

Q: "Is TOML better than JSON for config files?"

"For hand-edited configuration, usually yes — TOML's comments and readable structure make configs easier to maintain. JSON remains better when configs are generated or consumed by many different tools."

Q: "Can I convert TOML to JSON?"

"Yes, and it is lossless for standard data types. Our free TOML to JSON converter runs in your browser and converts either direction instantly."

Q: "Does JSON support comments?"

"No — standard JSON forbids comments, which is one of the biggest reasons developers switch configs to TOML or YAML. Some tools accept JSON with comments (JSONC), but it is not portable."

October 14, 2026 · 5 min read · By the DollarWise team

TOML vs JSON: Which Config Format Should You Use?

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If you have ever opened a package.json, wrestled with a pyproject.toml, or edited a config file by hand at 1 a.m., you have felt the difference between these two formats in your bones. JSON and TOML both store structured data, but they were built for different jobs — and picking the wrong one for a hand-maintained config file costs you readability, comments, and eventually your patience. Here is a practical comparison to help you choose, plus a free way to convert between them.

The one-paragraph version

JSON (JavaScript Object Notation) is a strict, machine-first data format: great for APIs and generated files, painful to edit by hand because it forbids comments and punishes a single missing comma. TOML (Tom’s Obvious Minimal Language) is a human-first config format: it supports comments, reads almost like an INI file, and maps cleanly onto the same data types. For configs humans edit, TOML usually wins; for data machines exchange, JSON usually wins.

Readability: where TOML pulls ahead

Compare the same server config in both formats:

# Server settings - edit freely
[server]
host = "0.0.0.0"
port = 8080
debug = false

[database]
url = "postgres://localhost:5432/app"
pool_size = 10

{
  "server": {
    "host": "0.0.0.0",
    "port": 8080,
    "debug": false
  },
  "database": {
    "url": "postgres://localhost:5432/app",
    "pool_size": 10
  }
}

The TOML version has comments, no nested braces, and no trailing-comma landmines. The JSON version works everywhere but reads like a tax form. When a config file is edited by humans — developers, DevOps engineers, power users — that readability gap compounds over hundreds of edits.

Feature-by-feature comparison

Comments. TOML has them (# like this); standard JSON does not, full stop. This alone decides many config migrations. JSONC (JSON with Comments) exists, but support varies by tool and it is not portable.

Strictness. JSON fails loudly on trailing commas, single quotes, or unquoted keys — which is actually a feature for machine-generated data, since it catches corruption. TOML is more forgiving in structure but stricter about types: it natively distinguishes dates, times, integers, and floats, while JSON’s only number type has caused infamous precision bugs with large integers.

Data types. TOML supports datetimes, multi-line strings, and arrays of tables out of the box. JSON sticks to strings, numbers, booleans, null, arrays, and objects — simpler, but datetimes become ambiguous strings.

Ecosystem. JSON is supported by literally everything: every language, every API, every tool. TOML support is broad in modern tooling (Rust’s Cargo, Python’s packaging, Hugo’s config) but still lags in older enterprise systems.

Nesting. JSON handles deeply nested structures naturally. TOML handles nesting via dotted keys and table headers, which gets awkward past two or three levels — a genuine weakness for very hierarchical configs.

When to choose TOML

Application config files edited by developers (pyproject.toml, Cargo.toml, Hugo configs).
Any file where comments matter — documenting why a value is set a certain way is priceless six months later.
Configs with dates, times, or precise numbers, where TOML’s richer types prevent ambiguity.
Projects already in the TOML ecosystem, like Python packaging or Rust tooling.

When to choose JSON

APIs and data exchange between systems — JSON is the universal language of web APIs.
Machine-generated configs that humans rarely touch (CI outputs, lockfiles, generated manifests).
Environments with limited tooling, where a TOML parser may not be available.
Deeply nested data that would become unwieldy as TOML tables.

Converting between the two

Switching formats is mechanical for standard data types — our free TOML to JSON converter translates either direction in your browser, no install needed. A couple of things to watch:

Comments do not survive conversion. JSON has nowhere to put them, so save a copy of the commented TOML for reference.
TOML datetimes become JSON strings. If downstream code parses them, confirm it handles the string format.
Key ordering may change. TOML tables flatten to JSON objects; most parsers preserve insertion order, but do not rely on it.
Validate after converting. Paste the result into a JSON linter or TOML validator before deploying — one malformed file can take down a deploy.

TOML and JSON in the wild: where you will meet each

You rarely get to choose in a vacuum — the ecosystem often chooses for you. You will meet TOML in Python’s pyproject.toml, Rust’s Cargo.toml, Hugo and Zola site configs, and Poetry/uv settings. You will meet JSON in package.json, tsconfig.json, CI pipeline definitions, API responses, VS Code settings, and browser extension manifests. When a project already speaks one format, match it rather than fighting the tooling. And when you inherit a JSON config that begs for comments, converting it to TOML (where the tool allows) is one of the highest-leverage cleanups you can do.

Frequently asked questions

What is the main difference between TOML and JSON?

TOML is designed to be written and read by humans — it has comments, clean table syntax, and rich data types. JSON is a stricter machine-first format built for data interchange, and it does not allow comments.

Is TOML better than JSON for config files?

For hand-edited configuration, usually yes: comments and readable structure make TOML configs far easier to maintain. JSON stays better when configs are machine-generated or consumed by many different tools.

Can I convert TOML to JSON?

Yes, losslessly for standard data types. Our free TOML to JSON converter runs entirely in your browser and converts in either direction instantly — just note that comments are dropped going to JSON.

Does JSON support comments?

No. Standard JSON forbids comments entirely, which is one of the main reasons developers move hand-edited configs to TOML or YAML. JSONC variants exist but are not portable across tools.

#toml #json #configuration

Written by the DollarWise team

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