TOML to JSON converter — read Cargo.toml and pyproject.toml as JSON

How to use the TOML to JSON converter

1. Paste TOML into the Input box. The sample is a short Cargo.toml.
2. Choose the Indent: 2 spaces, 4 spaces or Compact.
3. Copy the JSON, or download it as config.json.

What it does and when to use it

Many tools read their settings from TOML, but scripts, dashboards and APIs usually want JSON. Converting lets you feed pyproject.toml metadata into a CI script, inspect a Cargo.toml with jq, or store a Hugo or Netlify config in a JSON database. It is also a good way to check how a TOML file nests: dotted headers such as [tool.ruff] are easy to misread, and the JSON makes each level explicit.

The reverse direction is JSON to TOML. To tidy a TOML file without converting it, use the TOML formatter, and for YAML configs try YAML to JSON.

How it works

The smol-toml library is loaded into your browser and parses the text under TOML 1.0 rules. It rejects anything invalid, such as a key defined twice, an unfinished string or a table header repeated. The parsed data then goes through JSON.stringify with your indent:

Nothing is sent to a server.

Worked examples

These are the tool’s own outputs.

The sample Cargo.toml. The single [[bin]] block becomes an array holding one object:

  "bin": [
    {
      "name": "cli",
      "path": "src/main.rs"
    }
  ]

A pyproject.toml with 4-space indent. [project] with a dependencies array and [tool.ruff] with line-length = 100 give a "project" object and a "tool" object that contains "ruff": { "line-length": 100 }.

Special values, compact. This TOML:

released = 1979-05-27T07:32:00-08:00
day = 1979-05-27
local = 07:32:00
hex = 0xff
inf = inf
ratio = 1.0

becomes {"released":"1979-05-27T07:32:00.000-08:00","day":"1979-05-27","local":"07:32:00.000","hex":255,"inf":null,"ratio":1}.

An unclosed string. title = 'unclosed returns “Invalid TOML document: unfinished string” with a caret at the opening quote.

Limits and tips

• Integers beyond 2^53 cannot be held exactly in JavaScript; the parser stops with an error rather than rounding them.
• Types are flattened as shown in the table, so a round trip back to TOML turns date strings into quoted strings.
• Key order is kept within each table.