# Yarn > Yarn package manager with workspaces. Use for JavaScript dependencies. Use when this capability is needed. - Skill: `tomevault-io/yarn` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/yarn` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/yarn/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/yarn --- # Yarn Yarn (Berry) is a modern package manager. It introduced Plug'n'Play (PnP) to eliminate `node_modules` and support **Zero Installs**. ## When to Use - **Monorepos**: Yarn Workspaces are robust and feature-rich (Constraints, plugins). - **Speed**: PnP is faster than node_modules linking. - **Correctness**: Strict phantom dependency checks prevent requiring packages you didn't list. ## Quick Start ```bash corepack enable yarn set version stable yarn init -2 # Install yarn add react ``` ## Core Concepts ### Plug'n'Play (PnP) Instead of copying files to `node_modules`, Yarn generates a `.pnp.cjs` map. Node requires are intercepted and resolved directly from the cache. ### Zero Installs Commit the `.yarn/cache` folder. Cloning the repo = Installation complete. No `yarn install` needed in CI. ### Constraints Enforce rules across workspaces (e.g., "All packages must use React 18"). ## Best Practices (2025) **Do**: - **Use Corepack**: Manage Yarn versions via Node's `corepack` tool. - **Use `yarn dlx`**: Equivalent to `npx`. - **Commit Cache**: If using Zero Installs, do commit the binary cache. **Don't**: - **Don't use Yarn 1**: Legacy Yarn (v1) is dead. Migrate to Berry (v4+). ## References - [Yarn Documentation](https://yarnpkg.com/) --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/g1joshi) — claim your Tome and manage your conversions.