Bun is an all-in-one JavaScript and TypeScript runtime that includes a fast package manager, bundler, test runner, and Node.js-compatible APIs. It natively executes TypeScript and JSX without a separate compilation step.
When to use: Fast server-side JavaScript, TypeScript-first projects, replacing Node.js for better startup performance, built-in SQLite, password hashing, file I/O, HTTP servers, bundling, and testing without external tooling.
When NOT to use: Projects requiring full Node.js ecosystem compatibility (some native modules unsupported), production environments needing battle-tested stability of Node.js, or browser-only code that does not need a runtime.
Bun JavaScript runtime, bundler, and package manager. Covers Bun.serve() HTTP server, Bun.file() I/O, SQLite, password hashing, Bun.build() bundler, bun:test runner, and package management. Use when building with Bun APIs, running scripts with Bun, bundling code, managing packages with bun install/add, or writing tests with bun:test. Source: oakoss/agent-skills.