TOML has become the default for modern developer tooling — Rust's Cargo.toml, Python's pyproject.toml, and countless CI configs — specifically because it supports comments and stays readable as a config grows. JSON remains the right call whenever a file is generated and consumed by machines rather than hand-edited: API payloads, data exports, and anywhere a strict, dependency-free parser matters more than human readability. If you're picking a config format that people will edit directly, TOML almost always wins; for machine-to-machine data, stick with JSON.
JSON
JSON is a strict, machine-oriented data format defined by curly braces, square brackets, quotes, and commas. It has no native comment syntax and makes no distinction between config-time and runtime data — a JSON file is just data.
Pros
- • 100% interoperability — every language and API tool parses it natively
- • Unambiguous machine parsing with no dialect variations (RFC 8259)
- • Compact for automated data exchange and REST payloads
- • Built into virtually every standard library — no extra dependencies
- • One universal spec, so tooling and editors have first-class support everywhere
Cons
- • No comments allowed — you can't document why a config value is set the way it is
- • Trailing commas and unquoted keys are invalid, making hand-edits error-prone
- • Deeply nested config gets hard to scan compared to TOML's flat table syntax
- • Built for machines first, not optimized for a human editing a config file by hand
Example
{
"database": {
"server": "192.168.1.1",
"ports": [8000, 8001]
}
} TOML
TOML (Tom's Obvious, Minimal Language) is a configuration file format designed to be easy for humans to read and edit, and unambiguous for machines to parse. It's the default format behind Cargo.toml (Rust) and pyproject.toml (Python).
Pros
- • Built explicitly for config files, not general data interchange
- • Supports inline and block comments — document your config in place
- • Clean table/array syntax that stays readable even when nested
- • Strongly typed values (dates, integers, floats) with no extra parsing logic
- • Default format for major toolchains: Cargo.toml, pyproject.toml, and more
Cons
- • Nesting can become wordy with repetitive table header declarations
- • Not designed for large payloads or wire transfer — it's a config format, not an API format
- • Fewer native parsers than JSON, especially outside mainstream languages
- • Less familiar to most developers than JSON, so there's a small onboarding curve
Example
[database] server = "192.168.1.1" ports = [ 8000, 8001 ]
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