JSON to TOML Converter

What is TOML and Why Convert from JSON?

// Convert JSON to TOML in Node.js using the smol-toml library
import { stringify } from 'smol-toml';

const data = JSON.parse(`{
  "package": { "name": "my-app", "version": "1.0.0" },
  "dependencies": { "serde": { "version": "1.0" } }
}`);

// The top-level value must be an object; null values on objects are dropped.
const toml = stringify(data);

console.log(toml);
// [package]
// name = "my-app"
// version = "1.0.0"
//
// [dependencies.serde]
// version = "1.0"

Key Features

Examples

{
  "package": {
    "name": "my-app",
    "version": "1.0.0",
    "edition": "2021"
  },
  "dependencies": {
    "serde": { "version": "1.0", "features": ["derive"] },
    "tokio": { "version": "1", "features": ["full"] }
  }
}

{
  "build-system": {
    "requires": ["hatchling"],
    "build-backend": "hatchling.build"
  },
  "project": {
    "name": "my-package",
    "version": "0.3.1",
    "requires-python": ">=3.10",
    "dependencies": ["requests>=2.31", "pydantic>=2.0"]
  }
}

{
  "title": "My Service",
  "debug": false,
  "port": 8080,
  "database": {
    "host": "localhost",
    "port": 5432,
    "pool_size": 10
  },
  "features": ["auth", "metrics", "tracing"]
}

{
  "servers": [
    { "name": "alpha", "ip": "10.0.0.1", "ports": [8001, 8002] },
    { "name": "beta", "ip": "10.0.0.2", "ports": [9001] }
  ]
}

{
  "build": {
    "command": "npm run build",
    "publish": "dist",
    "environment": { "NODE_VERSION": "20" }
  },
  "redirects": [
    { "from": "/old", "to": "/new", "status": 301, "force": true }
  ]
}

{
  "tool": {
    "ruff": { "line-length": 100, "target-version": "py310" },
    "black": { "line-length": 100 }
  }
}

How to Use

1. 1

   Paste Your JSON

   Enter or paste your JSON into the input field above. You can also click 'Load example' to try a Cargo.toml source, pyproject.toml source, or app settings object.

2. 2

   See Live TOML Output

   TOML appears instantly in the output panel. If your JSON has a top-level array or null values, the tool explains exactly what to do rather than producing broken output.

3. 3

   Copy or Download

   Click Copy to grab the TOML to your clipboard, or Download to save it as a .toml file ready for Cargo, Poetry, Hugo, Netlify, or any tool that reads TOML.

Common JSON-to-TOML Pitfalls

[1, 2, 3]

{ "items": [1, 2, 3] }

{ "name": "a", "nickname": null }

{ "name": "a", "nickname": "" }

{ "ports": [8001, null, 8003] }

{ "ports": [8001, 8003] }

{ 'name': 'a', 'active': true, }

{ "name": "a", "active": true }

{ "ratio": 1.0 }  →  ratio = 1

{ "ratio": 1.5 }  →  ratio = 1.5

{ "server": { "a": 1 }, "server": [1] }

{ "server": { "a": 1 }, "servers": [1] }

Common Use Cases

Generate Cargo.toml

Turn structured JSON — from a scaffolding tool, an API, or a script — into a valid Rust Cargo.toml, with nested [dependencies] tables and inline tables produced automatically.

Generate pyproject.toml

Convert JSON project metadata into a PEP 621 pyproject.toml, including dotted [tool.*] tables, so tooling that emits JSON can produce Python packaging config.

Human-Editable Config from JSON

Transform an application's JSON settings into a readable TOML config file that humans can comfortably edit, with comments added afterward by hand.

Deployment Config Generation

Produce netlify.toml, foundry.toml, or similar platform configs from JSON, turning nested objects and arrays of objects into the tables and arrays of tables those tools expect.

Config Format Migration

Move configuration from a JSON-based system to a TOML-based one, using this converter as the bridge and the null and top-level warnings to catch anything that will not map.

Prototyping TOML Structure

Sketch a config as JSON — a format most developers type fluently — then convert to TOML to see the idiomatic table and array-of-tables layout before committing it to a repo.

Technical Details

RFC 8259 JSON Parsing

JSON input is parsed with the browser's native JSON.parse(), which is fully RFC 8259 compliant. Before serialization, the tool checks that the top-level value is an object and scans for null values so it can warn about dropped object keys or reject a null inside an array with a precise path.

TOML 1.0.0 Output via smol-toml

TOML is generated with the smol-toml library, a zero-dependency, fully TOML 1.0.0-compliant serializer. Nested objects become tables, deeply nested objects become dotted tables, and arrays of objects become arrays of tables. Floats with a zero fractional part are written as integers per TOML rules, with a warning.

100% Browser-Based — No Upload, No Server

All processing happens in your browser's JavaScript engine. No data is transmitted at any point. Inputs larger than 200KB switch from live to manual mode (an explicit Convert click) to keep the interface responsive.

Best Practices

Wrap Top-Level Arrays Under a Key

If your data is naturally a JSON array, wrap it in an object with a descriptive key ({ "items": [...] }) before converting. TOML documents must be a table at the root, and the key gives your array a clear name in the output.

Decide What Nulls Should Mean

Before converting, decide whether a null field should disappear (drop the key) or carry a value. TOML will drop object nulls and reject array nulls, so resolving them in your JSON first gives predictable, complete output.

Use Nested Objects for Grouping

Group related settings into nested objects in your JSON — they become clean [tables] and dotted tables in TOML, which is far more readable than a flat list of keys, matching how Cargo and pyproject configs are organized.

Validate Your JSON First

If your JSON is hand-written or comes from an unreliable source, validate it with our JSON Formatter to catch trailing commas and quoting mistakes before converting to TOML.

Add Comments After Converting

JSON has no comments, so none carry over. Since TOML supports # comments, add documentation to the generated TOML by hand — one of the main reasons to move human-edited config to TOML in the first place.

Frequently Asked Questions