TOML

Tom's Obvious, Minimal Language (TOML, originally Tom's Own Markup Language)^[2] is a file format for configuration files.^[3] It is intended to be easy to read and write due to following commonplace syntax and semantics which aim to be minimal, and it is designed to map unambiguously to a dictionary. Originally created by Tom Preston-Werner, its specification is open source. TOML is used in a number of software projects^[4][5][6] and is implemented in many programming languages.^[7]

TOML
Filename extension	.toml
Internet media type	application/toml
Developed by	Tom Preston-Werner Community
Initial release	23 February 2013; 12 years ago (2013-02-23)
Latest release	1.0.0[1] 12 January 2021; 4 years ago (12 January 2021)
Type of format	Data interchange
Open format?	Yes
Website	toml.io

Syntax

TOML's syntax primarily consists of, among other constructs, key = value pairs, [section names], and # (for comments). TOML's syntax somewhat resembles that of .INI files, but it has one agreed-upon formal specification, whereas the .INI format suffers from many competing variants, many implicitly specified through project-specific parsers.

Exceeding stringly-typed semantics, TOML supports the data types string, integer, float, boolean, datetime, array and table.

Example

# This is a TOML document.

title = "ImpalaPay Co."

[database]
server = "192.168.1.1"
ports = [ 8000, 8001, 8002 ]
connection_max = 5000
enabled = true

# Line breaks are okay when inside arrays
hosts = [
  "alpha",
  "omega"
]

[servers]

  # Indentation (tabs and/or spaces) is allowed, but not required
  [servers.alpha]
  ip = "10.0.0.1"
  dc = "eqdc10"

  [servers.beta]
  ip = "10.0.0.2"
  dc = "eqdc10"

Use cases

TOML is used in a variety of settings (some related to its creator), such as:

• Jekyll (a static site generator) configuration _config.toml (although configuration through YAML is also supported)
• Hugo (a static site generator) configuration hugo.toml (although configuration through JSON or YAML are also supported)
• Python 3 package manifests pyproject.toml^[8]
• Rust package manifests Cargo.toml^[4]
• Julia project settings Project.toml and package manifests Manifest.toml^[9]
• Blender add-on manifests blender_manifest.toml^[10]
• Gradle version catalogs libs.versions.toml^[11]
• Taplo configurations .taplo.toml and taplo.toml^[12]
• Prettier configurations .prettierrc.toml^[13]

Criticism

TOML has been criticized on a number of points:^[14][15]

• TOML is verbose; it is not DRY and is syntactically noisy.
• TOML's hierarchies can be difficult to infer from syntax alone.
• Overcomplication: TOML has too many features.
• In TOML, the syntax determines the data types ("syntax typing").

Implementations

• Python 3: tomlib^[16]
• Taplo^[17]

See also

• Configuration file § File format
• INI file
• YAML