TOML to JSON Converter

How to convert TOML to JSON

1. Choose the direction: TOML → JSON (the default) or JSON → TOML.
2. Paste your data, or click Open a file to load a .toml or .json file (up to 10 MB).
3. For TOML → JSON, pick the Indentation (2 or 4 spaces) and decide whether to tick Big integers as strings. For JSON → TOML, keep or untick Omit null values.
4. Tick Sort keys if you want every table ordered alphabetically.
5. The result updates as you type; Convert runs it again on demand. Errors show the line and column of the problem.
6. Copy or download the result. Swap direction moves the output into the input to convert it back.

TOML and JSON side by side

TOML (Tom’s Obvious Minimal Language) is the configuration format behind Cargo.toml in Rust, pyproject.toml in Python, Hugo and Netlify sites, and many command-line tools. It is designed to be read and edited by people, and it maps directly onto a JSON-like tree of tables (objects), arrays and values.

[package]
name = "demo"
version = "0.1.0"

[[bin]]
name = "cli"

becomes

{"package": {"name": "demo", "version": "0.1.0"}, "bin": [{"name": "cli"}]}

• A [table] header becomes a JSON object, and dotted keys such as a.b.c = 1 become nested objects.
• An array of tables, [[bin]], becomes a JSON array of objects.
• Inline tables { x = 1 } and arrays work as you would expect. Comments are dropped, since JSON has none.

Where the two formats differ

Dates and times. TOML has four native date-time types; JSON has none. The converter writes them as ISO 8601 strings and keeps their flavour: an offset date-time stays 1979-05-27T07:32:00.000-08:00, a local date stays 1979-05-27, and a local time stays 07:32:00.000. Fractional seconds are kept to the millisecond. Converting back to TOML gives plain strings, because nothing in JSON marks them as dates.

Integers. TOML integers are signed 64-bit, from −9,223,372,036,854,775,808 to 9,223,372,036,854,775,807. JavaScript numbers, used by most JSON parsers, are only exact up to 2^53 (9,007,199,254,740,991). Larger TOML integers are written with all their digits, which is valid JSON, but a program that reads them as doubles will round them; tick Big integers as strings to avoid that. An integer outside the 64-bit range is rejected, as the TOML specification requires.

Special floats. inf, -inf and nan have no JSON form, so they are written as the strings "inf", "-inf" and "nan".

JSON → TOML. A TOML document is always a table, so the JSON must be an object at the top level. TOML has no null: by default null values are omitted and a message tells you how many; untick Omit null values to get an error with the location of the first one instead. JSON does not distinguish 1 from 1.0, so whole numbers become TOML integers, and numbers too large for 64 bits become floats. In recent browsers, big integers in your JSON keep their exact digits.