TOML to JSON

What is TOML to JSON Conversion?

TOML (Tom's Obvious Minimal Language) is a configuration file format designed for humans. It maps unambiguously to a hash table, supports nested tables, typed values, and inline comments. Many tools and frameworks use TOML as their primary config format: Rust projects rely on Cargo.toml, Python packaging uses pyproject.toml, and Hugo static sites configure via config.toml. Converting TOML to JSON online lets you transform these configuration files into a format that virtually every programming language, API, and data pipeline can consume natively.

JSON (JavaScript Object Notation), defined by RFC 8259, is the most widely supported data interchange format. While TOML prioritizes human readability with its minimal syntax and comment support, JSON prioritizes machine interoperability. A TOML to JSON converter bridges this gap by parsing TOML input according to the TOML v1.0.0 specification and emitting a structurally equivalent JSON document. The conversion preserves all data: strings, integers, floats, booleans, arrays, and tables map directly to their JSON counterparts.

TOML has four native date/time types that JSON cannot represent directly: offset date-times, local date-times, local dates, and local times. JSON has no date type, so these values are serialized as ISO 8601 strings during conversion.

Why Use a TOML to JSON Converter?

Configuration files written in TOML often need to feed into systems that only accept JSON. Rather than rewriting the file by hand or installing a parser library locally, a browser-based converter handles the transformation in seconds.

TOML to JSON Use Cases

TOML to JSON Type Mapping Reference

Every TOML type has a direct JSON equivalent, with one exception: date and time values. The table below shows how each TOML type converts to JSON. This mapping follows the TOML v1.0.0 specification and matches the behavior of standard parsers like tomllib (Python), toml-rs (Rust), and @iarna/toml (Node.js).

TOML integers support underscores for readability (e.g., 1_000_000) and hexadecimal (0xDEADBEEF), octal (0o755), and binary (0b11010110) literals. All of these convert to plain decimal numbers in JSON. TOML also supports infinity and NaN float values, but these have no JSON representation and will cause a conversion error in strict mode.

Code Examples

Working examples of TOML to JSON conversion in four languages. Each reads a TOML file, parses it, and outputs formatted JSON.

import { parse } from '@iarna/toml'
import fs from 'fs'

const toml = fs.readFileSync('config.toml', 'utf8')
const json = parse(toml)
console.log(JSON.stringify(json, null, 2))
// Input:  [server]
//         host = "localhost"
//         port = 8080
// Output: { "server": { "host": "localhost", "port": 8080 } }

import tomllib   # Python 3.11+ (standard library)
import json

with open('config.toml', 'rb') as f:
    data = tomllib.load(f)

print(json.dumps(data, indent=2, default=str))
# Dates become strings: "1979-05-27"
# Arrays of tables become JSON arrays of objects

package main

import (
    "encoding/json"
    "fmt"
    "os"

    "github.com/BurntSushi/toml"
)

func main() {
    var data map[string]any
    _, err := toml.DecodeFile("config.toml", &data)
    if err != nil {
        panic(err)
    }
    out, _ := json.MarshalIndent(data, "", "  ")
    fmt.Println(string(out))
}

# Using yj (YAML/JSON/TOML converter)
cat config.toml | yj -tj

# Using dasel
dasel -f config.toml -r toml -w json

# Using Python one-liner (3.11+)
python3 -c "import tomllib, json, sys; print(json.dumps(tomllib.load(sys.stdin.buffer), indent=2, default=str))" < config.toml

Frequently Asked Questions