Bun
All-in-one JavaScript/TypeScript runtime — fast Node.js-compatible runtime built in Zig with native bundler, package manager, and test runner. Bun features: bun run (execute JS/TS without transpilation), bun install (npm-compatible package manager, 10-25x faster), bun build (bundler, replaces webpack/esbuild), bun test (Jest-compatible test runner), native TypeScript execution (no tsc needed), Node.js API compatibility, Web APIs (fetch, WebSocket, crypto), Bun.serve() HTTP server, SQLite built-in (bun:sqlite), bun:ffi for native code, .env loading built-in, and bun --hot for hot reload. Single binary, cross-platform (macOS, Linux, Windows).
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Bun loads .env files automatically (no dotenv needed) — ensure .env not committed to git. bun:ffi allows calling native code — validate FFI inputs for agent security. Bun runs with same OS permissions as Node.js — no sandboxing by default.
⚡ Reliability
Best When
Building new JavaScript/TypeScript agent tools, scripts, or servers where fast startup, built-in TypeScript, and zero-config are priorities — Bun's all-in-one approach eliminates npm + webpack + ts-node + jest configuration overhead.
Avoid When
Your agent code depends on C++ native addons, you need maximum Node.js compatibility guarantees, or your organization requires a stable LTS runtime.
Use Cases
- • Agent TypeScript execution — bun agent.ts — runs TypeScript directly without tsc compilation step; agent scripts written in TypeScript execute immediately; no tsconfig.json or build step required for simple agent scripts
- • Agent fast package installation — bun install in 1.2 seconds vs npm install in 30 seconds; agent Docker builds use bun install for CI speed; bun.lockb lockfile is binary for faster parsing; bun add openai installs and updates package.json in one command
- • Agent HTTP server — Bun.serve({ port: 3000, fetch(req) { return new Response('Agent ready') } }) — built-in HTTP server with Web API fetch handler; agent webhook receivers and API servers start with zero config; Bun.serve handles 100K+ req/s on single core
- • Agent SQLite data — import { Database } from 'bun:sqlite'; const db = new Database('agent.db'); const rows = db.query('SELECT * FROM tasks').all() — built-in SQLite without npm package; agent persistent storage with zero dependencies; faster than better-sqlite3
- • Agent test suite — bun test — discovers *.test.ts files, runs Jest-compatible tests with describe/it/expect; agent test suites run 3-5x faster than Jest; bun test --watch re-runs on file change; no jest.config.js needed
Not For
- • Production Node.js replacement without testing — Bun has ~95% Node.js compatibility but edge cases exist; audit agent code for Node.js-only APIs before switching to Bun in production
- • Native npm ecosystem modules with C++ addons — some npm packages with native .node addons may not work with Bun; test critical agent dependencies before committing to Bun
- • Legacy CommonJS-heavy codebases — Bun prefers ESM; CJS works but mixing CJS/ESM in agent code causes require() vs import() confusion
Interface
Authentication
No auth — local JavaScript runtime. npm registry auth uses .npmrc or bun login for private registries.
Pricing
Bun is MIT licensed, maintained by Oven Inc. Free for all use including commercial.
Agent Metadata
Known Gotchas
- ⚠ bun.lockb is binary and not human-readable — bun install generates binary bun.lockb lockfile instead of package-lock.json; agent code reviews cannot diff bun.lockb in git; use bun install --frozen-lockfile in CI to prevent lockfile changes; commit bun.lockb to git for reproducible installs
- ⚠ Bun.serve() requires explicit return — fetch(req) { processRequest(req) } missing return undefined is valid JS but returns 404; agent HTTP handlers must return Response or Promise<Response>; missing return is silent bug in Bun.serve handlers
- ⚠ bun:test expect matchers differ from Jest — Bun's test runner is Jest-compatible but not 100% identical; some Jest matchers (toMatchInlineSnapshot with complex objects) may behave differently; agent test suites migrating from Jest should run full test suite to verify matcher compatibility
- ⚠ TypeScript decorators require experimentalDecorators — Bun's TypeScript transpiler supports decorators but requires experimentalDecorators: true in tsconfig.json; agent code using class decorators (@Injectable, @Controller) silently strips decorators without tsconfig; always include tsconfig.json for decorator-heavy agent frameworks
- ⚠ bun install --production flag required for deploy — bun install without --production installs devDependencies; agent production Docker images without --production flag include test dependencies and are 2-5x larger; use bun install --production in Dockerfile for minimal agent container size
- ⚠ Node.js vm module not fully supported — require('vm') / new vm.Script() may not work in Bun; agent sandboxing code using Node.js vm module for LLM output evaluation fails in Bun; use Bun's plugin system or separate process for agent code sandboxing
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Bun.
Scores are editorial opinions as of 2026-03-06.