TOML Syntax Cheat Sheet

TOML (Tom's Obvious Minimal Language) is a configuration format designed to be unambiguous to read and to map onto a hash table. It is used by pyproject.toml, Cargo.toml and many tools. Convert between formats with the TOML to JSON Converter and the JSON to TOML Converter.

A complete example

# A comment
title = "Example"
count = 42
ratio = 3.14
enabled = true
released = 2026-10-28
updated = 2026-10-28T07:32:00Z
tags = ["a", "b", "c"]
products = [
  { name = "Hammer", sku = 738594937 },
  { name = "Nail", sku = 284758393 },
]

[server]
host = "localhost"
port = 8080

[server.tls]
enabled = false

Value types

Tables, dotted keys and arrays of tables

• A [table] header starts a section; every key below it belongs to that table until the next header.
• [a.b] defines table b inside a. The same key path can only be defined once.
• Dotted keys such as a.b.c = 1 create nested tables without headers: the result is {"a": {"b": {"c": 1}}}.
• A header with the name wrapped in doubled square brackets (two opening brackets, the name, two closing brackets, no spaces) appends a new table to an array of tables. Each repeated header adds one element; an array of inline tables, as in the example, does the same on one line.

Rules that trip people up

• Keys are case-sensitive and unquoted keys may only use A-Za-z0-9_-. Quote anything else: "my key" = 1.
• A key cannot be defined twice, and [server] after server.port = 1 is an error.
• Integers have no leading zeros (007 is invalid) and floats need digits on both sides of the dot (.5 and 5. are invalid).
• There is no null. Leave the key out, or use an empty string or a documented sentinel.
• Arrays may mix types in TOML 1.0, but most tools expect one type.
• Whitespace is not significant, unlike YAML, but a value must end its line.