What is an array of tables in TOML?

Double square brackets like [[products]] append a new table to an array each time they appear. Repeating the header three times builds an array of three table objects, which is how TOML expresses a list of structured records.

How many string types does TOML have?

Four: basic strings in double quotes with backslash escapes, multiline basic strings in triple double quotes, literal strings in single quotes with no escaping, and multiline literal strings in triple single quotes. Literal strings are ideal for Windows paths and regular expressions.

What date and time formats does TOML support?

TOML has four first-class temporal types based on RFC 3339: offset date-time with a timezone, local date-time without a zone, local date only, and local time only. They are written without quotes, for example 1979-05-27T07:32:00Z.

What is the difference between a table and an inline table?

A table is opened with a header line in square brackets and its keys follow on subsequent lines. An inline table is written on a single line in curly braces and must be fully defined at once; you cannot add keys to it later.

Can a TOML key be defined more than once?

No. Defining the same key twice, or redefining a table already defined, is a hard error. This strictness is intentional and is one of the main ways TOML prevents the silent overrides that plague looser config formats.

TOML Syntax Reference

Email me this result

Get this tool's output sent to your inbox, plus one useful tool a week. No spam, unsubscribe any time.

A tour of TOML v1.0.0 syntax

TOML (Tom’s Obvious, Minimal Language) is a configuration format designed to be easy to read and to map cleanly onto a hash table. It powers Cargo.toml, pyproject.toml and many other tool configs. This reference covers keys and tables, every string variant, number formats, arrays and the four date-time types.

How it works

A TOML file is a set of key/value pairs grouped into tables. A header in square brackets opens a table; dotted names create nesting; double brackets build an array of tables:

title = "Example"

[server]
host = "127.0.0.1"
ports = [80, 443]
tls = { enabled = true, min = "1.2" }

[[products]]
name = "A"
[[products]]
name = "B"

created = 1979-05-27T07:32:00Z

Every value has a clear type: integers (with _ separators and 0x/0o/0b prefixes), floats, booleans (true/false only), strings in four flavours, arrays, and the RFC 3339 temporal types. Files must be valid UTF-8.

Tips and notes

Use literal strings (single quotes) for Windows paths and regex to avoid escaping.
[[name]] appends to an array of tables; plain [name] defines a single table.
Booleans are lowercase only; there is no True or yes.
Defining the same key twice is an error — that strictness prevents silent overrides.