Setting Up a MERN Monorepo Using Yarn Workspaces

A monorepo (short for "monolithic repository") is a single repository that contains multiple projects, which can be related or unrelated. This setup is helpful for developers as it simplifies dependency management, improves development workflow, and supports better code sharing between projects.

In this guide, we'll walk through setting up a MERN (MongoDB, Express, React, Node.js) project inside a monorepo using Yarn Workspaces.

monorepo-mern/
├── client     # React + Vite + TypeScript
├── server     # Express + TypeScript
└── README.md

Setup with Yarn

Run yarn init in the root of the project directory, and then install concurrently package.

yarn init -y
yarn add concurrently -W

The -W flag installs the package at the workspace root level (i.e., "W" for "workspace-root").

Edit the root package.json to include your client and server folders as workspaces:

"workspaces": [
    "server",
    "client"
],

then cd into client and install the package using yarn similarly do for server folder. Add to configure scripts for client & server.

# scripts for client
"scripts": {
    "dev": "vite",
    "build": "tsc -b && vite build",
    "format": "prettier --write .",
    "format:check": "prettier --check .",
    "lint": "eslint .",
    "lint:fix": "eslint . --fix",
    "preview": "vite preview"
},

# scripts for server
"scripts": {
    "build": "tsc -b",
    "start": "tsc -b && node ./dist/index.js",
    "dev": "nodemon --exec ts-node ./src/index.ts",
    "clean": "rm -rf dist/ .logs/",
    "format": "prettier . --write",
    "format:check": "prettier . --check",
    "lint": "eslint .",
    "lint:fix": "eslint . --fix"
},

At the root package.json, configure scripts to run both client and server simultaneously:

"scripts": {
  "dev": "concurrently \"yarn workspace client dev\" \"yarn workspace server dev\"",
  "build": "concurrently \"yarn workspace client build\" \"yarn workspace server build\"",
  "format": "concurrently \"yarn workspace client format\" \"yarn workspace server format\"",
  "lint": "concurrently \"yarn workspace client lint\" \"yarn workspace server lint\"",
  "clean": "concurrently \"yarn workspace client clean\" \"yarn workspace server clean\""
}

🧠 concurrently lets you run multiple scripts in parallel, which is perfect for monorepos.

Troubleshooting Tips

• Make sure you run yarn at the root after every major change.

• If you face any issues related to package mismatches or missing dependencies:

  • Run yarn install again at the root.

  • Clear the cache using yarn cache clean.

  • Double-check your workspace paths in package.json.

Summary

Using a monorepo with Yarn Workspaces in a MERN stack app offers:

• Centralised dependency management

• Easier simultaneous development

• Cleaner and modular project structure

This structure is especially useful in team-based or full-stack projects, helping streamline both frontend and backend workflows.

Final Note

This setup is just a foundation. You can further improve it by:

• Adding a .env management tool like dotenv

• Adding shared packages or types

• Using tools like Turborepo or Nx for advanced workflows