---
name: yarn-3cf4a50fc210
description: Expert Yarn package manager assistance covering Yarn Berry (v4+), Zero-Installs, PnP (Plug'n'Play), and workspaces. Use when managing fast, deterministic JavaScript monorepo dependencies.
---

# 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

- **Modern JavaScript Package Management (Yarn v4+)**: Fast, reliable dependency management with Corepack support.
- **Plug'n'Play (PnP) & Zero-Installs**: Eliminating `node_modules` folders for instant workspace switching and CI runs.
- **Enterprise Monorepos**: Coordinated workspace resolution, constraints, and release workflows.
- **Hardened Security & Integrity**: Strict lockfile checksums and automated dependency audits.

## Quick Start

```bash
corepack enable
yarn set version stable
yarn init -2

# Install
yarn add react
```

## Core Concepts

### Modern Yarn Configuration (.yarnrc.yml)

Configuring node-modules linker or Plug'n'Play:

```yaml
# .yarnrc.yml
nodeLinker: node-modules # Use 'pnp' for Zero-Installs, 'node-modules' for standard compatibility
compressionLevel: mixed
enableGlobalCache: true

packageExtensions:
  "@types/react@*":
    peerDependencies:
      react: "*"
```

### Workspace Commands in Monorepos

Executing commands across workspaces:

```bash
# Run build command in parallel across all workspaces
yarn workspaces foreach --parallel --verbose run build

# Run tests only on workspaces changed relative to main branch
yarn workspaces foreach --since=main run test

# Add dependency to a specific workspace
yarn workspace @my-org/web-app add swr
```

### Upgrading Dependencies with Interactive CLI

Upgrading packages adhering to SemVer:

```bash
# Interactively review and upgrade outdated packages
yarn upgrade-interactive

# Re-validate lockfile integrity
yarn install --immutable
```

## Common Patterns

### Yarn Berry Monorepo Workspaces with TypeScript Loose Mode

**Problem**: Slow installs and node_modules bloat across multiple internal monorepo packages.

**Solution**:
Configure Yarn Berry workspaces with `.yarnrc.yml`:

```yaml
# .yarnrc.yml
nodeLinker: node-modules # Use node-modules linker for maximum ecosystem compatibility
yarnPath: .yarn/releases/yarn-4.5.0.cjs

packageExtensions:
  "react-scripts@*":
    dependencies:
      "typescript": "*"
```

Root `package.json`:

```json
{
  "private": true,
  "workspaces": ["apps/*", "packages/*"]
}
```

## Best Practices

**Do**:

- Target modern Yarn (v4+) enabled through Corepack (`corepack enable yarn`).
- Use `yarn install --immutable` in CI/CD pipelines to prevent unintended lockfile updates.
- Leverage `yarn workspaces foreach` with `--since=main` to test only modified packages in monorepos.
- Use `packageExtensions` in `.yarnrc.yml` to cleanly resolve missing peer dependency warnings from older third-party packages.

**Don't**:

- Use legacy Yarn 1.x (Classic); migrate to modern Yarn v4+ for enhanced performance and security.
- Edit `yarn.lock` manually; resolve conflicts via `yarn install`.
- Mix npm or pnpm lockfiles within a Yarn repository.

## Troubleshooting

| Error                                                    | Cause                                                            | Solution                                                                |
| :------------------------------------------------------- | :--------------------------------------------------------------- | :---------------------------------------------------------------------- |
| `Usage Error: Couldn't find the node_modules state file` | Project running under PnP mode when tools expect `node_modules`. | Set `nodeLinker: node-modules` in `.yarnrc.yml` and run `yarn install`. |
| `YN0002: Missing peer dependency`                        | Package requires peer dependency not declared in consumer.       | Declare missing package in root `.yarnrc.yml` `packageExtensions`.      |
| `Yarn command not found`                                 | Yarn Berry binary missing in `.yarn/releases/`.                  | Run `corepack enable && corepack use yarn@stable`.                      |

## References

- [Yarn Documentation](https://yarnpkg.com/)


---
Source attribution: G1Joshi
Original project: https://github.com/G1Joshi/Agent-Skills/blob/6a74cf03a8a86dc7d993ead3091b41123dbd0181/skills/devops/yarn/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2026 G1Joshi

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: G1Joshi
Original project: https://github.com/G1Joshi/Agent-Skills/blob/6a74cf03a8a86dc7d993ead3091b41123dbd0181/skills/devops/yarn/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering
Roles: Backend Developer, Frontend Developer, Full-Stack Developer
Specialties: Backend, Cross Platform, Frontend
Tools: Yarn
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: c3b155f22caeb0e41f2980f340a141b86c4faead34b15eb300b1f33669522099