This is a comprehensive reference guide for migrating TypeScript library projects from tsup to tsdown, the newer Rolldown-powered bundler. It covers the full migration path: renaming config files, transforming options like cjsInterop to cjsDefault, moving external and noExternal into a deps namespace, and handling the different defaults (tsdown defaults to ESM and auto-enables DTS). The guide includes explicit mappings for deprecated options, alternatives for unsupported features like splitting and metafile, and package.json updates. Use this when you need to port a tsup build setup to tsdown or troubleshoot compatibility issues. The detail level is thorough enough that an agent can execute the migration without guessing.
npx skills add https://github.com/rolldown/tsdown --skill tsdown-migrate