🧳TOML and JSON Converter

Converts TOML and JSON both ways and lists the values a round trip cannot restore.

Where a round trip is not lossless

In TOMLTurned into JSONConverted back
Date and time typesJSON has no unquoted date type, so it becomes a stringStays a string; the date type is gone
A float such as 1.0Folded into one JSON numberComes back as the integer 1
inf and nanJSON has no notation for themCannot be restored
64-bit integersJSON numbers are exact in JavaScript only up to 2 to the 53rdTrailing digits can change
Inline tablesBecome the same object as a standard tableThe original notation is unknown
Array tablesBecome an array of objectsIndistinguishable from inline objects
Comments and key orderNot carried overStay missing

The supported range covers basic and literal strings including multi-line forms, integers with hex, octal and binary notation, floats, booleans, all four date and time types, arrays, inline tables, standard tables, array tables and dotted keys. In the other direction, JSON null has no TOML notation and is reported as an error.

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About this tool

This converter turns TOML configuration into JSON and JSON back into TOML. Pick a direction, paste the source, and the result appears immediately; a syntax error is reported with the line and what went wrong. Below the result it counts top-level keys, values in total, standard tables and array tables so you can confirm the structure moved across the way you expected.

The point of this tool is less the conversion than the round-trip loss. TOML has unquoted date and time types and distinguishes integers from floats, while JSON does neither. Once a value leaves for JSON and comes back, a date has become a string and 1.0 has become the integer 1. Checking the TOML 1.0.0 specification against JSON as of October 2026, the tool lists those values with their key paths and the table below explains which notations cannot be restored and why.

The supported range covers strings and multi-line strings, integers and floats, booleans, all four date and time types, arrays, inline tables, standard tables, array tables and dotted keys. JSON null has no TOML counterpart and is reported as an error. Schema validation and config merging are not performed.

Frequently asked questions

Why does a date end up inside quotes?

TOML has dedicated date and time types written without quotes, and JSON has no such type. The moment a value moves to JSON it becomes a string, and it stays a string on the way back. This tool collects those values so the change is visible.

Why is JSON null not converted?

TOML 1.0.0 has no notation meaning null. Replacing it with an empty string or zero would change the meaning, so the tool refuses to guess, names the key involved and stops.

What does this tool not do?

It does not validate against a schema, merge config files or convert YAML or XML. It converts between TOML and JSON and reports round-trip loss.