tsdown

tsdown is an elegant library bundler built on Rolldown (Rust-based), providing a complete out-of-the-box solution for building TypeScript and JavaScript libraries. It handles source transformation, multiple output formats (ESM, CJS, IIFE, UMD), TypeScript declaration file generation, and package.json exports field generation with sensible defaults.

When to use: Building TypeScript libraries for npm, generating declaration files, producing dual ESM/CJS packages, bundling CLI tools, library development with watch mode, migrating from tsup.

When NOT to use: Application bundling (use Vite/Rolldown directly), server-side rendering frameworks (use framework bundlers), projects that need Webpack-specific features, simple scripts that need no bundling.

tsdown TypeScript 捆綁器基於 Rolldown 構建，用於庫和包。在捆綁 TypeScript 程式庫、產生聲明檔或發布 npm 套件時使用。用於 tsdown、bundler、rolldown、dts、宣告、函式庫建置、esm、cjs、treeshake。 來源：oakoss/agent-skills。