.env.development -

The validation script checks that required .env.development keys exist before the app starts. For complex microservice architectures, you can combine multiple files:

# .env.development REACT_APP_API_URL=http://localhost:3001 REACT_APP_ENABLE_MOCKS=true Next.js supports .env.development natively but distinguishes between build-time and run-time variables. You must prefix browser-safe variables with NEXT_PUBLIC_ . .env.development

const z = require('zod'); const envSchema = z.object( API_URL: z.string().url(), PORT: z.string().transform(Number).default('3000'), DEBUG_MODE: z.enum(['true', 'false']).transform(v => v === 'true') ); The validation script checks that required

const env = envSchema.parse(process.env); Here is the golden rule: Anything in a browser-facing .env.development is public. A user can open DevTools and see your REACT_APP_ variables. Never, ever put an admin password, database URI, or private key in a frontend .env.development file. Use a backend proxy instead. Common Pitfalls and How to Fix Them Even experienced developers fall into these traps. Let's troubleshoot the most common problems. Pitfall 1: "My .env.development variables are not loading." Diagnosis: You likely changed the file after the server started. Most dev servers (Webpack, Vite) only read environment files at startup. const z = require('zod'); const envSchema = z

# settings.py import environ env = environ.Env() environ.Env.read_env(os.path.join(BASE_DIR, '.env.development')) To prevent your project from descending into "environment variable hell," follow these battle-tested principles. 1. Always Commit .env.development (With Care) This is a controversial point. You should not commit .env.production (it contains secrets). However, .env.development should be committed to your repository because it contains no real secrets—only local URLs, mock keys, and safe defaults. Committing it ensures all developers on your team have the same baseline configuration.

The .env.development file is a used exclusively when your application runs in a development environment.