JSON to TOML Converter

TOML is a configuration format designed to be obvious to read: Python's pyproject.toml, Rust's Cargo.toml, Hugo, Netlify and many CLI tools use it. This converter maps JSON objects to TOML tables and arrays of objects to arrays of tables, following the TOML 1.0 specification.

1. Paste a JSON object or drop a .json file.
2. Nested objects become [tables], arrays of objects become [[arrays of tables]].
3. Read any notice: TOML has no null, so null values are left out.
4. Copy the TOML or download a .toml file.

Example

{
  "title": "My site",
  "server": { "host": "0.0.0.0", "port": 8080, "tls": false },
  "plugins": [
    { "name": "sitemap", "enabled": true },
    { "name": "analytics", "enabled": false }
  ]
}

title = "My site"

[server]
host = "0.0.0.0"
port = 8080
tls = false

[[plugins]]
name = "sitemap"
enabled = true

[[plugins]]
name = "analytics"
enabled = false

The server object becomes a [server] table and the plugins array of objects becomes two [[plugins]] entries — the idiomatic way to write lists of records in TOML.

How JSON maps to TOML

• Objects → tables ([server]), nested objects → dotted tables ([tool.ruff]).
• Arrays of objects → arrays of tables ([[plugins]]).
• Arrays of values → inline arrays (select = [ "E", "F" ]).
• Strings, numbers and booleans keep their types; keys with special characters are quoted.
• null has no TOML equivalent and is omitted, with a notice.
• A TOML document must be a table, so a top-level JSON array is placed under [[records]].

Where TOML is used

Python packaging (pyproject.toml for pip, uv, Poetry, Hatch, Ruff and Black), Rust (Cargo.toml), Hugo site configuration, Netlify (netlify.toml), Deno, Gitea, InfluxDB/Telegraf and many more. It is a good choice whenever humans edit configuration by hand.

Dates and comments

TOML has native date and time types, but JSON stores dates as strings, so they remain quoted strings in the output. Add # comments to the TOML afterwards — one of its advantages over JSON.

Real-world examples

Create a pyproject.toml section

Python packaging uses TOML. Writing metadata as JSON first — or reusing it from another tool — and converting avoids TOML quoting mistakes.

{
  "project": {
    "name": "dataswitch-demo",
    "version": "0.3.1",
    "requires-python": ">=3.10",
    "dependencies": ["pandas>=2.2", "openpyxl"]
  }
}

[project]
name = "dataswitch-demo"
version = "0.3.1"
requires-python = ">=3.10"
dependencies = [ "pandas>=2.2", "openpyxl" ]

Configure a Rust or Hugo project

Cargo.toml and Hugo's config use nested tables. Nested JSON objects become [section.subsection] headers.

{
  "package": { "name": "csv-tool", "version": "1.0.0", "edition": "2021" },
  "dependencies": { "serde": { "version": "1.0", "features": ["derive"] } }
}

[package]
name = "csv-tool"
version = "1.0.0"
edition = "2021"

[dependencies.serde]
version = "1.0"
features = [ "derive" ]

Common errors and how to fix them

Related guides

• How to flatten nested JSON into a CSV table

Convert JSON to TOML in code

For one-off files the tool above is quickest. To automate the same task in a script or pipeline, these snippets are a good starting point.

Python (tomli-w)

import json
import tomli_w  # pip install tomli-w

with open("config.json", encoding="utf-8") as f:
    data = json.load(f)

with open("config.toml", "wb") as f:
    tomli_w.dump(data, f)

Node.js (smol-toml)

import { stringify } from "smol-toml";  // npm install smol-toml
const toml = stringify(JSON.parse(text));

Frequently asked questions

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