Understanding package.json File

What is package.json?

package.json is the heart of every Node project. It records metadata, dependencies, scripts, and configuration — telling npm everything about your project.

A Complete Example

{
  "name": "my-app",
  "version": "1.0.0",
  "description": "A demo app",
  "main": "index.js",
  "scripts": {
    "start": "node index.js",
    "dev": "nodemon index.js",
    "test": "jest"
  },
  "dependencies": {
    "express": "^4.18.0"
  },
  "devDependencies": {
    "jest": "^29.0.0"
  }
}

Key Fields

Field	Purpose
name / version	Identity
scripts	Run commands
dependencies	Production packages
devDependencies	Dev-only tools
main	Entry point

Version Symbols

"express": "4.18.0"    // exact
"express": "^4.18.0"   // minor + patch updates
"express": "~4.18.0"   // patch updates only

FAQs

What does ^ mean?

Allow updates that don't change the leftmost non-zero number (minor/patch). More in our NPM guides.

Should I edit it by hand?

You can, but use npm install to add dependencies safely.