bun

Getting Started

1. Install the skill using the command above
2. Open your AI coding agent (Claude Code, Codex, Gemini CLI, or Cursor)
3. Reference the skill in your prompt
4. The AI will use the skill's capabilities automatically

Example Prompts

• "Review the open pull requests and summarize what needs attention"
• "Generate a changelog from the last 20 commits on the main branch"

Overview

Bun is an all-in-one JavaScript/TypeScript runtime that replaces Node.js, npm, webpack, and Jest with a single binary. It provides native TypeScript support, a high-performance HTTP server (Bun.serve()), a fast package manager, a bundler, and a Jest-compatible test runner with dramatically faster performance.

Instructions

• When creating HTTP servers, use Bun.serve() which handles 100K+ req/s with built-in WebSocket support, TLS, and streaming responses.
• When managing packages, use bun install (10-30x faster than npm), bun add, bun remove, and prefer bun.lock (text format) for readable git diffs.
• When bundling, use Bun.build() with appropriate target ("browser", "bun", "node"), enable code splitting with splitting: true, and configure tree shaking.
• When writing tests, use bun test with Jest-compatible API (describe, it, expect), snapshot testing, mocking with mock.module(), and --coverage for code coverage.
• When doing file I/O, prefer Bun.file() and Bun.write() over Node.js fs for significantly faster file operations, and use Bun.Glob for pattern matching.
• When handling authentication, use Bun.password.hash() and Bun.password.verify() for bcrypt/argon2 instead of npm packages.
• When migrating from Node.js, replace node with bun in scripts, keep package.json unchanged, and note that most npm packages work without modifications. Use bun:sqlite for embedded databases instead of SQLite npm packages.

Examples

Example 1: Build a high-performance API server

User request: "Create a REST API using Bun's built-in HTTP server"

Actions:

1. Create server with Bun.serve() and route handler
2. Parse JSON bodies with request.json() and return Response objects
3. Add WebSocket upgrade for real-time features
4. Use Bun.password for auth and bun:sqlite for data storage

Output: A fast API server using only Bun built-ins with no external dependencies.

Example 2: Migrate a Node.js project to Bun

User request: "Switch my Express project from Node.js to Bun"

Actions:

1. Replace npm install with bun install in CI and local setup
2. Update package.json scripts to use bun run instead of node
3. Replace dotenv with Bun's built-in .env loading
4. Switch test runner from Jest to bun test with same test files

Output: A Bun-powered project with faster installs, startup, and test execution.

Guidelines

• Use Bun.serve() for new HTTP servers; it is significantly faster than Express on Bun.
• Prefer Bun.file() and Bun.write() over Node.js fs for file operations.
• Use bun:sqlite for local data instead of adding SQLite npm packages.
• Use Bun.password for auth instead of bcrypt/argon2 npm packages for zero native dependencies.
• Keep bun.lock (text format) in git for readable diffs.
• Test with bun test instead of Jest for the same API with dramatically faster execution.
• When targeting browsers, use Bun.build() with target: "browser".