TOML

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

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]

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=5000enabled=true# Line breaks are okay when inside arrayshosts=["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

References

1. "Release 1.0.0". 12 January 2021. Retrieved 17 January 2021.
2. Preston-Werner, Tom (2013-02-24). "Initial commit · toml-lang/toml@84db252". GitHub . Archived from the original on 2024-06-15. Retrieved 2024-06-15.
3. Preston-Werner, Tom; Gedam, Pradyun (January 11, 2021). "TOML: English v1.0.0". Archived from the original on January 29, 2024. Retrieved January 27, 2024.
4. "The Manifest Format - The Cargo Book". doc.rust-lang.org. Archived from the original on 2019-08-26. Retrieved 2023-07-08.
5. DeVault, Drew (2021-07-28). "My wish-list for the next YAML". Archived from the original on 2024-03-09. Retrieved 2021-07-28. 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.
6. "TOML: Tom's Obvious Minimal Language". toml.io. Archived from the original on 2022-08-08. Retrieved 2022-08-08.
7. "toml-lang/toml". GitHub. 23 May 2022. Archived from the original on 15 February 2017. Retrieved 16 December 2016.
8. "PEP 518 – Specifying Minimum Build System Requirements for Python Projects | peps.python.org". Python Enhancement Proposals (PEPs). Retrieved 2025-02-04.
9. "10. Project.toml and Manifest.toml · Pkg.jl". pkgdocs.julialang.org. Archived from the original on 2023-07-08. Retrieved 2023-07-08.
10. Blender Documentation Team (2025-08-17). "How to Create Extensions ; Manifest" . Retrieved 2025-08-17.
11. Gradle, Inc. (2025). "Version Catalogs" . Retrieved 2025-08-17.
12. Ferenc Tamás (2022-06-16). "Configuration File" . Retrieved 2025-08-17.
13. "Configuration File" . Retrieved 2025-08-17.
14. What is wrong with TOML?
15. An INI critique of TOML
16. "tomllib — Parse TOML files". Python documentation. Archived from the original on 2024-06-11. Retrieved 2023-07-08.
17. Ferenc Tamás. "Taplo ; A versatile, feature-rich TOML toolkit" . Retrieved 2025-08-17., Ferenc Tamás. "Taplo (source repository)" . Retrieved 2025-08-17.