$ man environment-files
Engineering · Data Formats
Environment Files
Files that store environment variables for local development.
why it matters
.env files keep secrets out of Git. API keys, tokens, database URLs. They're local only. Each developer has their own. Vercel has its own set for production.
how you use it
Create .env in your project root. Add API_KEY=value. Add .env to .gitignore. Load variables with process.env.API_KEY in code.
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