TOML

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 = [ 8001, 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"
]

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[6], as well as a discussion of using TOML for parametrization of simulation modeling.[7]

TOML is much easier to implement correctly than YAML. The YAML specification was pointed out to have 23,449 words, while TOML specification had only 3,339 words.[8]

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
• TOML forbids to populate a table in different steps, thus making the merge of several configuration files problematic
• TOML arbitrarily introduces a syntax for dates
• TOML allows (but discourages) the creation of keys with a name that is an empty string
• 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

• INI File
• HJSON
• Recfiles
• YAML