Prettier Kotlin Plugin

2.1.0 verified Sat Apr 25 auth: no javascript

Prettier plugin for Kotlin language formatting. v2.1.0 (latest) ditched the original JS-based printer in favor of kastree's Kotlin Writer, a significant breaking change from v1.x. The parser (kotato) is alpha-stage, based on kastree, and can parse most Kotlin code but has performance issues. Release cadence is irregular with long gaps. Key differentiator: integrates Kotlin formatting into Prettier's ecosystem, allowing uniform code style across JS/TS/CSS/Kotlin projects. Lacks stable and full Kotlin grammar support; not recommended for production.

Common errors

error Cannot find module 'prettier-plugin-kotlin' ↓

cause Plugin not installed or not in node_modules.

fix

Run 'npm install --dev prettier prettier-plugin-kotlin' in your project root.

error Error: Cannot parse file. Unsupported syntax: ... ↓

cause The kotato parser does not support all Kotlin syntax or the file contains errors.

fix

Simplify the code or fix syntax errors. For advanced features, use ktlint instead.

error Cannot read properties of undefined (reading 'type') ↓

cause Plugin is outdated or Prettier version mismatch.

fix

Update both prettier and prettier-plugin-kotlin to latest: npm install prettier@latest prettier-plugin-kotlin@latest

Warnings

breaking v2.0.0 replaced the JavaScript-based printer with a Kotlin-based one (kastree Writer). Output may differ significantly from v1.x. ↓

fix Reformat all Kotlin files with the new plugin version. Review diff of formatted files for regressions.

gotcha Parser (kotato) is alpha; may fail on complex Kotlin syntax (e.g., inline classes, contracts, multi-file inference). ↓

fix For production, use kotlinc or ktlint. Only use this plugin for experimental or simple projects.

gotcha VSCode Prettier extension may not auto-detect the plugin for Kotlin files; formatOnSave may not work despite manual formatting succeeding. ↓

fix Restart VSCode after installing plugin. Set 'prettier.requireConfig': false if needed. See https://github.com/prettier/prettier-vscode/issues/395

deprecated v1.x plugin used a different printer; upgrade to v2.x for current support. ↓

fix Update to version 2.1.0: npm install prettier-plugin-kotlin@latest

Install

npm install prettier-plugin-kotlin

yarn add prettier-plugin-kotlin

pnpm add prettier-plugin-kotlin

Imports

default plugin registration
wrong
```
import prettierPluginKotlin from 'prettier-plugin-kotlin'
```
correct
```
prettier.config.js -> module.exports = { plugins: ['prettier-plugin-kotlin'] }
```
Prettier automatically discovers plugins named 'prettier-plugin-*' in node_modules. No explicit import needed unless you pass plugins array manually (ESM compatible).

require (CommonJS)

wrong

const prettierPluginKotlin = require('prettier-plugin-kotlin'); prettierPluginKotlin.format(code)

correct

const prettier = require('prettier'); const code = prettier.format('fun main() {}', { parser: 'kotlin', plugins: [require('prettier-plugin-kotlin')] })

Do not call the plugin directly. Pass it as a plugin to prettier.format(). The plugin does not expose its own format function.

ESM (type: module)

wrong

import * as prettier from 'prettier'

correct

import prettier from 'prettier'; const code = await prettier.format('fun main() {}', { parser: 'kotlin', plugins: ['prettier-plugin-kotlin'] })

Prettier v3+ is ESM-only. Use dynamic import or top-level await. The plugin string is auto-resolved.

Quickstart

Demonstrates formatting a simple Kotlin function with Prettier using the Kotlin plugin in ESM mode.

// Ensure prettier and prettier-plugin-kotlin are installed
// npm install prettier prettier-plugin-kotlin

import prettier from 'prettier';

const code = `fun main(args: Array<String>) { println("Hello, World!") }`;

const formatted = await prettier.format(code, {
  parser: 'kotlin',
  plugins: ['prettier-plugin-kotlin'],
  tabWidth: 2,
  semi: false
});

console.log(formatted);
// Expected output:
// fun main(args: Array<String>) {
//   println("Hello, World!")
// }