TOML
This article relies too much on references to primary sources. (January 2021) |
Filename extension |
.toml |
---|---|
Internet media type | Not registered[1] |
Developed by | Tom Preston-Werner Community |
Initial release | 23 February 2013 |
Latest release | v1.0.0 (January 11, 2021 ) |
Type of format | Data interchange |
Open format? | Yes |
Website | toml |
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][4] and is implemented in many programming languages.[2] The name "TOML" is an acronym for "Tom's Obvious, Minimal Language"[5] referring to its creator, Tom Preston-Werner.
Syntax[]
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.
Example[]
# 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 as introduced at SciPy 2017,[citation needed] as well as a discussion of using TOML for parametrization of simulation modeling.[6]
Format | Formal standard | Strongly typed | Human-readable | Allows comments |
---|---|---|---|---|
JSON | Yes[7] | Yes | Yes | No |
YAML | Yes[8] | Yes | Yes | Yes |
TOML | No, formal specification | Yes | Yes | Yes |
INI | No, multiple dialects | No | Yes | Yes |
Criticism[]
Since its first release TOML has received several critiques. The StrictYAML project lists the following points as problematic in TOML:[9]
- 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,[10] 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[]
References[]
- ^ There is a mime type proposal for TOML consisting in
application/toml
, but this has never been officially registered among IANA's Media Types. - ^ Jump up to: a b "toml-lang/toml". GitHub.
- ^ "The Manifest Format - The Cargo Book". doc.rust-lang.org.
- ^ Drew DeVault (2021-07-28). "My wish-list for the next YAML".
YAML is both universally used, and universally reviled. It has a lot of problems, but it also is so useful in solving specific tasks that it’s hard to replace. Some new kids on the block (such as TOML) have successfully taken over a portion of its market share, but it remains in force in places where those alternatives show their weaknesses.
- ^ "toml-lang/toml". January 15, 2021 – via GitHub.
- ^ "toml-intro.rst". subversion.american.edu.
- ^ "The JavaScript Object Notation (JSON) Data Interchange Format".
- ^ "YAML™ Specification Index".
- ^ What is wrong with TOML?
- ^ An INI critique of TOML
External links[]
- Configuration files
- Computer file formats
- Lightweight markup languages