JSON vs YAML vs TOML: Which Configuration Format to Use
A practical comparison of the three most common configuration formats with use cases.
Configuration files run modern infrastructure. Picking the wrong format multiplies friction across an entire team for years.
JSON: The Universal Default
JSON wins on tooling: every language parses it, every editor highlights it, every linter validates it.
{ "port": 8080, "debug": true, "hosts": ["a.com", "b.com"] }
Pain points: no comments, trailing commas forbidden, verbose for human editing.
Use it for: API payloads, machine-generated config, package manifests (package.json).
YAML: Readable but Treacherous
YAML reads like a memo and writes like a minefield.
port: 8080
debug: true
hosts:
- a.com
- b.com
Famous footguns: Norway problem (no parses as false), implicit type coercion, indentation-sensitive errors.
Use it for: Kubernetes manifests, GitHub Actions, Ansible — anywhere the ecosystem demands it. Always quote strings that look like numbers, booleans, or dates.
TOML: Boring on Purpose
TOML aims to be obvious, with no surprises.
port = 8080
debug = true
hosts = ["a.com", "b.com"]
[database]
url = "postgres://localhost"
Wins: comments, no indentation games, sections, dates as first-class. Loses: less ubiquitous parsers, awkward for deeply nested data.
Use it for: Rust (Cargo.toml), Python (pyproject.toml), and anywhere humans hand-edit config.
Decision Matrix
|-----------|------|------|------|
If your team hand-edits, prefer TOML. If your tools force YAML, accept it but enable schema validation. Reserve JSON for machine handoffs.
Use the [JSON Formatter](https://sdk.is/json-formatter) and [YAML Validator](https://sdk.is/yaml-validator) to catch errors early.