$ man environment-variables

Environment Variables

Secret values like API keys that you don't want in your code.

by Shawn Tenam

API keys, database passwords, MCP tokens. These can't live in your repo. They'd be public on GitHub. Environment variables let you reference them without exposing them.

Create a .env file locally with API_KEY=your_key_here. Add it to .gitignore so it never gets committed. On Vercel, add the same variables in the dashboard so your deployed site can access them.