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|Internet media type||Not registered|
|Developed by||Tom Preston-Werner|
|Initial release||23 February 2013|
(January 11, 2021 )
|Type of format||Data interchange|
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,[non-primary source needed] and is implemented in many programming languages. The name "TOML" is an acronym for "Tom's Obvious, Minimal Language" 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" [owner] name = "Tom Preston-Werner" dob = 1979-05-27T07:32:00-08:00 # First class dates [database] server = "192.168.1.1" ports = [ 8000, 8001, 8002 ] connection_max = 5000 enabled = true [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" [clients] data = [ ["gamma", "delta"], [1, 2] ] # Line breaks are OK when inside arrays hosts = [ "alpha", "omega" ]
Comparison to other formats
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, as well as a discussion of using TOML for parametrization of simulation modeling.
|Format||Formal standard||Strongly typed||Easy implementation||Human-readable||Allows comments|
|YAML||Yes||Yes||No[better source needed]||Yes||Yes|
- 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")
- 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
- There is a mime type proposal for TOML consisting in
application/toml, but this has never been officially registered among IANA's Media Types.
- "toml-lang/toml". GitHub.
- "The Manifest Format - The Cargo Book". doc.rust-lang.org.
- "toml-lang/toml". January 15, 2021 – via GitHub.
- "toml-intro.rst". subversion.american.edu.
- "YAML spec is also super complicated and writing parser for it is non-trivial (fo... | Hacker News". news.ycombinator.com.
- What is wrong with TOML?
- An INI critique of TOML