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Filename extension
Internet media typeNot registered[1]
Developed byTom Preston-Werner
Initial release23 February 2013; 8 years ago (2013-02-23)
Latest release
(January 11, 2021; 3 months ago (2021-01-11))
Type of formatData interchange
Open format?Yes Edit this at Wikidata

TOML is a file format for configuration files. It is intended to be easy to read and write due to obvious semantics which aim to be "minimal", and is designed to map unambiguously to a dictionary. Its specification is open-source, and receives community contributions. TOML is used in a number of software projects,[2][3][non-primary source needed] and is implemented in many programming languages.[2] The name "TOML" is an acronym for "Tom's Obvious, Minimal Language"[4] referring to its creator, Tom Preston-Werner.


TOML's syntax primarily consists of key = "value" pairs, [section names], and # comments. TOML's syntax somewhat resembles that of .INI files, but it includes a formal specification, whereas the INI file format suffers from many competing variants.

Its specification includes a list of supported data types: String, Integer, Float, Boolean, Datetime, Array, and Table.


# This is a TOML document.

title = "TOML Example"

name = "Tom Preston-Werner"
dob = 1979-05-27T07:32:00-08:00 # First class dates

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


  # Indentation (tabs and/or spaces) is allowed but not required
  ip = ""
  dc = "eqdc10"

  ip = ""
  dc = "eqdc10"

data = [ ["gamma", "delta"], [1, 2] ]

# Line breaks are OK when inside arrays
hosts = [

Comparison to other formats[edit]

The following table draws on the TOML specification to make a comparison to other popular configuration formats (INI, JSON, and YAML). See also BespON as introduced at SciPy 2017,[citation needed] as well as a discussion of using TOML for parametrization of simulation modeling.[5]

Format comparison
Format Formal standard Strongly typed Easy implementation[citation needed] Human-readable Allows comments
JSON Yes Yes Yes Yes No
YAML Yes Yes No[6][better source needed] Yes Yes
TOML Yes Yes Yes Yes Yes
INI No No Yes Yes Yes


Since its first release TOML has received several critiques. The StrictYAML project lists the following points as problematic in TOML:[7]

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

The libconfini project has since released a more extensive critique of TOML from the INI perspective,[8] listing the following points (among others) as problematic:

  • TOML lets the configuration file decide about data types (syntax typing), when de facto it is the client application that decides, and any mismatching type will be anyway either ignored or converted to the expected type (depending on the parser)
  • TOML re-introduces what human-friendly languages normally try to get rid of: a verbose syntax and the necessity of using quotes for strings
  • TOML syntax is always case-sensitive, despite the fact that there are situations where configuration files must be case-insensitive (as, for instance, configuration files that map a FAT32 filesystem or HTML tags)
  • TOML uses square brackets for arrays, although square brackets are already reserved for table names; furthermore any special syntax for arrays brings the language back to syntax typing
  • A TOML table must be populated in a single step, so merging multiple TOML files is problematic
  • TOML arbitrarily introduces a syntax for dates
  • TOML allows (but discourages) the empty string as a key
  • TOML's rules cannot be inferred from the content, therefore editing a TOML file requires prior knowledge of the language
  • TOML is backward-incompatible with INI

See also[edit]


  1. ^ There is a mime type proposal for TOML consisting in application/toml, but this has never been officially registered among IANA's Media Types.
  2. ^ a b "toml-lang/toml". GitHub.
  3. ^ "The Manifest Format - The Cargo Book".
  4. ^ "toml-lang/toml". January 15, 2021 – via GitHub.
  5. ^ "toml-intro.rst".
  6. ^ "YAML spec is also super complicated and writing parser for it is non-trivial (fo... | Hacker News".
  7. ^ What is wrong with TOML?
  8. ^ An INI critique of TOML

External links[edit]