Rolldown

Overview

Rolldown is a Rust-based JavaScript bundler designed to replace Rollup — and eventually become Vite's production bundler. Built on OXC (the Rust toolchain behind oxlint), it aims for full Rollup API compatibility with 10-100x better performance. Currently in active development; when stable, Vite will use Rolldown instead of Rollup for production builds, unifying dev and prod bundling.

When to Use

• Rollup builds are slow on large projects
• Want to prepare for Vite's future bundler
• Building libraries where Rollup-compatible output matters
• Need faster bundling than Rollup without switching to webpack/esbuild
• Following the OXC ecosystem (oxlint → Rolldown → OXC resolver)

Instructions

Setup

npm install -D rolldown

Basic Configuration

// rolldown.config.js — Rollup-compatible config format
import { defineConfig } from "rolldown";

export default defineConfig({
  input: "src/index.ts",
  output: {
    dir: "dist",
    format: "esm",
    sourcemap: true,
  },
});

Library Build

// rolldown.config.js — Build a library with multiple outputs
import { defineConfig } from "rolldown";

export default defineConfig({
  input: "src/index.ts",
  external: ["react", "react-dom"],  // Don't bundle peer deps
  output: [
    {
      dir: "dist",
      format: "esm",
      entryFileNames: "[name].js",
      sourcemap: true,
    },
    {
      dir: "dist",
      format: "cjs",
      entryFileNames: "[name].cjs",
      sourcemap: true,
    },
  ],
});

With Plugins

// rolldown.config.js — Using Rollup-compatible plugins
import { defineConfig } from "rolldown";
import resolve from "@rollup/plugin-node-resolve";
import commonjs from "@rollup/plugin-commonjs";

export default defineConfig({
  input: "src/index.ts",
  plugins: [
    resolve(),       // Resolve node_modules
    commonjs(),      // Convert CommonJS to ESM
  ],
  output: {
    dir: "dist",
    format: "esm",
  },
});

Build Commands

# Build
npx rolldown -c

# Build with specific config
npx rolldown -c rolldown.config.js

# Watch mode
npx rolldown -c --watch

Migration from Rollup

// package.json — Swap the dependency
- "rollup": "^4.0.0"
+ "rolldown": "^1.0.0"

// Config is compatible — rename if needed
// rollup.config.js → rolldown.config.js (optional)

// Most Rollup configs work unchanged. Key differences:
// ✅ TypeScript built-in — no @rollup/plugin-typescript needed
// ✅ Node resolve built-in — @rollup/plugin-node-resolve often unnecessary
// ✅ Most Rollup plugins compatible — plugin API is the same
// ⚠️ Some advanced plugin hooks may differ — check docs

Examples

Example 1: Migrate a Rollup library build

User prompt: "My library uses Rollup and builds are slow. Migrate to Rolldown."

The agent will swap rollup for rolldown, remove unnecessary plugins (TypeScript and node-resolve are built-in), and benchmark the improvement.

Example 2: Prepare a Vite project for Rolldown

User prompt: "I want to be ready when Vite switches to Rolldown. What should I do?"

The agent will audit the current Vite config for Rollup-specific plugin usage, identify potential compatibility issues, and suggest config changes.

Guidelines

• Rollup-compatible config — same format, most plugins work
• TypeScript built-in — no separate TypeScript plugin needed
• Still in development — API may change; check compatibility for production use
• Vite integration coming — Rolldown will replace Rollup in Vite's production builds
• OXC ecosystem — part of the Rust JS toolchain (oxlint, oxc-resolver, Rolldown)
• 10-100x faster than Rollup — Rust parallelism over JavaScript
• Tree shaking built-in — same quality as Rollup
• ESM-first — designed for modern JavaScript output
• Watch mode supported — --watch for development
• Plugin compatibility — @rollup/plugin-* packages generally work