Pick any modern software project and you will find configuration files. They are usually written in one of three formats: JSON, YAML, or TOML. All three can represent the same data, but they make different trade-offs. This guide compares them honestly so you can pick the right one for your situation — and convert between them when you need to.

The 30-second summary

• JSON — strict, verbose, everywhere. Use for data interchange (APIs, storage). Painful to hand-edit.
• YAML — clean, indentation-based, very common in DevOps (Kubernetes, CI). Easy to hand-edit, easy to break.
• TOML — explicit, table-based, popular in Rust and Python tooling. Strict but readable.

Side-by-side example

The same configuration in all three formats:

JSON

{
  "name": "my-app",
  "version": "1.2.3",
  "database": {
    "host": "localhost",
    "port": 5432
  },
  "tags": ["api", "internal"]
}

YAML

name: my-app
version: 1.2.3
database:
  host: localhost
  port: 5432
tags:
  - api
  - internal

TOML

name = "my-app"
version = "1.2.3"
tags = ["api", "internal"]

[database]
host = "localhost"
port = 5432

Strengths and weaknesses

JSON

Strengths: universal parser support, strict spec, no ambiguity, mandatory quoting prevents surprises.

Weaknesses: no comments, mandatory double quotes everywhere, no multiline strings, verbose, does not natively support dates.

YAML

Strengths: very readable for humans, supports comments, multiline strings, anchors, and multiple documents per file.

Weaknesses: the spec is enormous and surprising (the Norway problem, implicit typing turning yes/no/on/off into booleans), indentation errors silently corrupt data, and many parsers disagree on edge cases.

TOML

Strengths: explicit and unambiguous, native support for dates and tables, very predictable parsing, popular in the Rust ecosystem (Cargo.toml) and Python (pyproject.toml).

Weaknesses: deeply nested data gets awkward (each level needs a new [table] header), less universal tooling than JSON or YAML.

When to use which

• APIs and machine-to-machine data: JSON. Always.
• Kubernetes, GitHub Actions, CI configs: YAML, because the ecosystem requires it.
• Rust / Python project configs: TOML, where the ecosystem has converged.
• Anything hand-edited by humans that does not need to be YAML for ecosystem reasons: consider TOML. The explicitness pays off.
• Anything that needs to round-trip through code: JSON is the safest bet because there is no parser ambiguity.

Converting between them

Often you do not get to pick — a tool expects one format and you have another. All of these conversions are lossy in edge cases (YAML's tags, TOML's tables-of-tables), but for typical config data they round-trip cleanly. We provide free, client-side converters for every direction:

• JSON → YAML
• YAML → JSON
• JSON → TOML
• JSON → XML

All conversions run entirely in your browser using the same parsers each ecosystem uses in production (js-yaml, @iarna/toml, fast-xml-parser). Nothing is uploaded.

A security note

Config files often contain secrets. Whatever format you use, be careful where you paste them for formatting or inspection. The 2025 JSONFormatter.org leak was caused by exactly this — users pasting real configs into a server-side formatter that exposed them publicly. Every converter linked above runs locally; there is no backend to leak. See our security page for details.