What is a TOML file?
TOML — unambiguous configuration
Use the format TOML
A concrete example
Prepare a JSON from a TOML file for an application.
Useful checks
Check dates, arrays, and nested sections. Comments are not part of JSON data.
Choose a conversion
Keep the original and open the result in the software or on the device that will need to use it.
Your questions about this format
Why does my JSON change structure when converted to CSV?
CSV represents a table of rows and columns. JSON can contain objects and nested lists that do not transpose directly. Convert a copy, check how the fields are represented, and keep the JSON if your usage requires retaining its entire structure.
How can one avoid losing the leading zeros in identifiers?
When opening the CSV in a spreadsheet, import the identifier columns as text. Automatic opening can turn 00123 into 123. Also check the dates and decimal separators before re-saving.
Can I convert a file containing secrets?
Remove passwords, API keys, and other secrets before sending a sample to the service or support. File processing is done online. For data that must not leave your device, use a suitable local tool.
Why aren't all outputs offered?
Formats are not interchangeable in all cases. ConvertLab displays the conversions from its catalog; renaming an extension does not change the content. Specialized outputs like certain XML exports or spreadsheets are identified as NoLimit.
What is it?
TOML is a configuration format built to deliver what YAML never quite managed: the complete absence of ambiguity. Every value has an explicit type, and there's never more than one way to read the same line.
Its syntax echoes old-school INI files — bracketed sections, keys and values — but backed by a rigorous specification.
History & origin
Tom Preston-Werner, co-founder of GitHub, created TOML in 2013, in direct response to YAML's pitfalls.
It has established itself as the configuration format of choice in several major ecosystems, notably Rust and, more recently, Python.
Why it is useful
No ambiguity, explicit types, excellent readability, and support for comments.
It handles dates natively, which JSON does not.
Limits & drawbacks
Deeply nested structures quickly become unwieldy: this isn't its strong suit.
It's less widespread than YAML or JSON, and its tooling is more limited.
Practical tips
TOML excels as a configuration file format, where clarity matters more than compactness.
For data exchange or complex structures, convert it to JSON.
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