Yarn

Package manager for JavaScript projects that doubles as a project manager. Handles installing, updating, configuring, and removing dependencies while supporting everything from single-package apps to large monorepos. Focuses on speed, correctness, security, and developer experience.

First package manager with native workspace support, later adopted by tools like Lerna. Maintained as a fully independent open-source project with a contributor-driven roadmap, used by projects such as Babel and Jest. Unlike package managers that delegate non-install commands to npm, Yarn reimplements all commands for full control over stability and behavior.

Key capabilities:

• Native workspaces with cross-references, focused installs, and parallel script execution
• Plug'n'Play as the default install strategy, replacing node_modules with a single loader file for faster installs and ghost dependency protection
• Zero-installs option: commit the cache to Git and skip install when switching branches
• Constraints engine for enforcing rules across workspaces, similar to ESLint for dependency hygiene
• Offline mirror and global cache to mutualize packages across projects and reduce install time

Teams adopt Yarn for monorepos with core packages and add-ons, multi-package publishing without cross-repo PRs, and strict dependency boundaries. CI pipelines benefit from focused installs that only pull in needed workspaces and from offline mirrors that remove reliance on the npm registry. Semantic error messages help developers quickly fix ghost dependencies and peer dependency issues before they surface in production.