Skypack

Skypack is a JavaScript CDN (Content Delivery Network) specifically optimized for serving npm packages as ES modules (ESM) to browsers and other JavaScript runtimes. Developed by the Skypack team at the Pika project (led by Fred K. Schott), it solves a critical problem in modern web development: most npm packages are published in CommonJS or UMD formats that cannot be directly imported as ES modules in browsers or in environments like Deno, Cloudflare Workers, and Vercel Edge Functions. Skypack automatically converts npm packages from CommonJS to ESM on-the-fly, caching the result for fast delivery via a global CDN. Unlike traditional CDNs like unpkg or jsDelivr that serve raw package files as-is, Skypack performs intelligent transformation to ensure the package is fully ESM-compatible. Key features include: automatic CommonJS to ESM conversion with dependency resolution and bundling, support for both bare module imports (via import maps or bundler transforms) and full URL imports (import React from the Skypack URL), intelligent caching that serves previously-converted packages instantly, support for TypeScript type definitions (automatically serving type declarations alongside the JavaScript code), streaming and on-demand compilation (packages are compiled lazily on first request, then cached globally), support for query parameters for controlling the output (e.g., minification, version pinning), a free tier for all open-source projects, and a dedicated enterprise plan with SLA guarantees for production use. Skypack also provides a package lookup and documentation service. While newer CDNs like esm.sh have gained popularity, Skypack remains an important part of the ESM-first web development ecosystem. As of 2026, the project has over 1,800 GitHub stars.