When you’re building a web app using React or Next.js, one of the first commands you’ll encounter is:
npm run dev
Many beginners run it simply because tutorials say so, without knowing what’s actually happening. Based on my development experience, this command is far more important than it looks.
■ What “npm run dev” really means
In simple terms, it’s a switch that launches your project in development mode.
Your code doesn’t become a working web app until you run this command. Once executed, your project becomes immediately viewable in your browser — typically at:
http://localhost:3000
Internally, in a Next.js project, npm run dev triggers:
next dev
This launches a local development server with live updates.
■ What actually happens under the hood
- A local server starts
- Your app becomes visible in the browser
- Any code changes update instantly (hot reload)
- React components re-render automatically
- Tailwind or CSS updates reflect immediately
- Errors appear instantly in the terminal or browser
This creates a tight development loop:
edit → save → see the result → repeat.
■ Why beginners get confused
Because it looks like a “magic command.”
But in truth, it’s simply a shortcut defined inside your package.json:
"dev": "next dev"
So npm run dev just means “run whatever is written under dev.”
Once you know this, the command becomes far less mysterious.
■ How it’s used in real development
Whenever I build a Next.js application, the first thing I do is start this development server.
It lets me check:
- layout and responsive design
- button interactions
- form behavior
- API calls
- styling updates
—all in real time, without waiting.
■ Summary
npm run dev is not just a command — it’s the core of your development workflow. Understanding it early makes your learning smoother and your development much faster.
