Opinionated TOML code formatter written in JavaScript.

Usage no npm install needed!

<script type="module">
  import aduh95TomlPrettifier from 'https://cdn.skypack.dev/@aduh95/toml-prettifier';


TOML Prettifier

Opinionated TOML code formatter written in JavaScript.


Reading a TOML file using Node.js and overwrite it with the prettified version:

import { createReadStream, createWriteStream, promises as fs } from "fs";
import { join } from "path";
import { tmpdir } from "os";
import { createInterface as readLines } from "readline";

import TOMLPrettifier from "@aduh95/toml-prettifier";

 * Prettifies a TOML file.
 * @param {string | URL | Buffer} inputFilePath
export async function prettifyTOMLFile(inputFilePath) {
  // Read the input file line by line.
  const reader = readLines({
    input: createReadStream(inputFilePath),
    crlfDelay: Infinity,
  // Create a temporary file to write the prettified TOML.
  const { handle, path: tmpFile } = await fs.mkstemp(join(tmpdir(), "pretty-"));
  const writer = createWriteStream(tmpFile, { fd: handle.fd });

  // Pass the input to TOMLPrettifier.
  for await (const line of TOMLPrettifier(reader)) {
    // Write the output to the temp file.
    writer.write(line + "\n");
  // Close the temp file once filled up.
  await handle.close();

  // Replace the input file by the temp file.
  await fs.rename(tmpFile, inputFilePath);

Web and Deno usage

The API is the same, although you must init the @aduh95/toml package manually before using it. This uses a WASM module that must be initiate asynchronously and is used to prettify arrays and inline tables.

import TOMLPrettifier from "@aduh95/toml-prettifier";
import initTOMLWasm from "@aduh95/toml";

await initTOMLWasm();


There are no available configuration for the formatting.

  • Keys: unquote the keys when possible.
  • Multiline basic strings: wrapped to 80 char, and indented one level below the opening and closing char sequence.
  • Multiline literal strings: No transformations are made.
  • Comments:
    • They respect indentation.
    • One or several #s represent the start of a comment, followed by one space unless the comment is empty.
  • Arrays: If an array can fit on one line, it will be reformated to one line, otherwise each element will be on a new line, with a trailing comma.
  • Inline tables: keys are alphabetically ordered.
  • Empty lines: conserved, but any space is removed.