JSON to TOML Converter (YAML to TOML too)

TOML configuration files — Cargo.toml, pyproject.toml, Hugo and Netlify settings — are easier to read than JSON, but writing them by hand from existing data is fiddly: nested objects become [tables], lists of objects become [[arrays of tables]], keys with dots or spaces need quotes, and plain values must come before any table. This converter does all of that from JSON or YAML, then reads its own TOML back with a TOML 1.0 parser to confirm nothing changed.

How to use this tool

1. Paste JSON (an object) or YAML (a mapping).
2. Decide what happens to null values, which TOML cannot store.
3. Optionally write small objects as inline tables and ISO date strings as TOML dates.
4. Copy the TOML into your .toml file.

Formula

object → [table] · array of objects → [[array of tables]] · other arrays → [ … ] · text with line breaks → """…"""

Inside every table the plain values come first and the sub-tables after them, which TOML requires; the order of keys is otherwise kept. Keys that are not made only of letters, digits, _ and - are quoted. JSON numbers keep their exact spelling (1.0 stays a float, long integers keep every digit); integers must fit in 64 bits. Strings are escaped as TOML basic strings. Dates are only converted when you ask, because "2024-02-29" may be meant as text.

Example

The sample becomes plain values first — title = "My App", tags = ["web", "api"] and the multi-line motd — then [server], [database] with its url, [database.pool], and two [[users]] blocks for Ada and Lin: five headers in all. With "inline tables" on, {"pt": {"x": 1, "y": 2}} is written pt = { x = 1, y = 2 }.