dependencies vs devDependencies in package.json

This post is pretty quick but I wanted to write about when you're supposed to use dependencies vs dev dependencies for installing packages.

In Node.js projects, the package.json file typically has two sections for listing packages your project uses: dependencies and devDependencies. Although both sections declare package requirements, they serve different purposes:

1. dependencies

• These are packages required at runtime for your application to function.
• When you deploy your project to production or run npm install --production, only these packages (and their transitive dependencies) are installed.
• Example: a web application using express would list express in dependencies because it's needed when the app is running.

2. devDependencies

• These are packages only needed during development—for tasks like testing, building, linting, or other development workflows.
• They are not required at runtime in production.
• When you install with npm install --production (or if NODE_ENV=production is set), these packages are not installed.
• Example: a testing framework such as jest or a code linter like eslint would live under devDependencies, since these tools are only used while developing.

In summary, anything your app needs to run in production belongs in dependencies, while anything you only need to develop and test your app belongs in devDependencies.