What Are .env Files? Keeping Secrets Out of Your Code

You've probably seen your AI assistant generate code that references process.env.SOMETHING. You've probably also seen it tell you to "create a .env file." But what exactly is happening here, and why does it matter so much?

The Problem .env Files Solve

Here's the core issue: your code needs to know your API keys to function, but your code also gets shared — pushed to GitHub, deployed to servers, copied between machines. If the keys are in the code, they go everywhere the code goes.

The solution is separation. Keep the keys in a separate file that doesn't travel with your code.

That file is the .env file.

How .env Files Work

A .env file is just a text file with key-value pairs:

# .env
STRIPE_SECRET_KEY=sk_live_abc123def456
DATABASE_URL=postgresql://user:password