TOML file format: what it is and how to use it

TOML is the config format that chose clarity: obvious types, minimal syntax, comments allowed, powering Cargo, pyproject and a generation of tools. Learn when to use it and what to choose instead.

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What is a TOML file?

A .toml file is configuration in TOML, Tom's Obvious Minimal Language: key = value pairs in [tables] with real types (strings, numbers, dates, arrays, inline tables), comments allowed, and a spec that prioritizes being unambiguous over being clever. It is the format of Cargo.toml, pyproject.toml and a generation of modern tooling that wanted INI's readability with JSON's data model.

When should you use TOML?

  • Tool configuration: Rust, Python and modern dev tools standardized on it.
  • Human-edited configs: comments and obvious types without YAML's whitespace traps.
  • Structured settings: typed values that map cleanly to data structures.

When is another format a better fit?

For pure machine interchange JSON is more universal; for deeply nested or document-heavy configs YAML is more common; for Apple's world PLIST. TOML's sweet spot is exactly what it was designed for: readable config files.

The short version: TOML is the config format that respects humans: obvious, typed and comment-friendly.

How to open a TOML file

On Windows

Double-click the file, or open it with Notepad++.

On macOS

Any text editor opens TOML files on macOS.

In your browser

Open TOML files right in a browser tab or with the dexrr viewer. No install, no upload.

Also opens in

  • Any text editor
  • VS Code
  • Notepad++

View or convert TOML files

A quick preview or a new format. No install, no upload.

View TOML files Preview and inspect TOML files Convert to TOML Turn files into TOML TOML to YAML YAML TOML to JSON JavaScript Object Notation TOML to PLIST Property List

TOML technical details

Full name
TOML configuration file
Extensions
.toml
MIME type
application/toml, text/plain
Compression
None (uncompressed)
Developer
Tom Preston-Werner
Specification
toml.io

TOML questions, answered

How do I open a .toml file?

Any text editor or IDE, syntax highlighting exists everywhere. dexrr displays and converts toml files directly in your browser.

Can I convert TOML files online?

Yes, dexrr converts toml locally in your browser: TOML to JSON or TOML to YAML for different ecosystems.

Is TOML better than YAML?

For config files many prefer it: no whitespace-significance traps, obvious types. YAML still dominates where deep nesting and existing ecosystems live.

Is TOML better than JSON?

For human-edited configs, yes: comments, clearer syntax, friendlier types. For machine interchange, JSON remains the standard.

Is the TOML format outdated?

No, it is the rising standard for tool configuration, entrenched in Rust, Python and modern dev tooling.