: If you are running a local instance of MongoDB or PostgreSQL, you can define your DATABASE_URL here.
: When working with third-party services like OpenAI, you can store your personal OPENAI_API_KEY here so it doesn't leak into the repository. .env.development.local
: Variables here only load when the application is running in "development" mode (e.g., via npm run dev or npm start ). The Hierarchy of .env Files : If you are running a local instance
(Highest priority for local development) .env.local .env.development .env (Lowest priority; general defaults) .env.development.local