.env.development Here

PAYMENT_GATEWAY=http://localhost:9090/mock-stripe

The implementation varies slightly, but the philosophy is identical. .env.development

Solution: Double-check your .gitignore. Add: PAYMENT_GATEWAY=http://localhost:9090/mock-stripe

.env.local
.env.*.local
.env.production
# But keep .env.development if it has safe defaults

CRA popularized the pattern of .env.development. It automatically loads: The implementation varies slightly, but the philosophy is

Important caveat: In React apps (and most frontend frameworks), environment variables must be prefixed with REACT_APP_ (or VITE_, NEXT_PUBLIC_) to be exposed to the browser.

# .env.development
REACT_APP_API_URL=http://localhost:3001
REACT_APP_ENABLE_MOCKS=true

The most common horror story in software is a developer accidentally running DROP DATABASE on the production server. By using .env.development, you explicitly point your development server to a local or staging database. Even if your code has a destructive bug, your production data remains untouched.