.env Best Practices

Reference: dotenv.space — the complete .env guide for every stack.

Core Rules (Never Break These)

1. Never commit .env — add it to .gitignore before the first commit, not after.
2. Always commit .env.example — strip real values, keep all variable names and comments.
3. Rotate immediately if exposed — deleting the file is not enough. Git history retains it. Use git filter-repo or BFG Repo Cleaner AND rotate every key.
4. Bots scan GitHub continuously. Exposed keys are found within minutes of a push.
5. Every env var is a string. Parse types explicitly in application code.

The File Hierarchy

The .gitignore Template

# .env files — never commit
.env
.env.local
.env.production
.env.staging
.env.*.local

# DO commit this — do not add to .gitignore:
# .env.example

The .env.example Template Pattern

# Application
APP_NAME=MyApp
SECRET_KEY=CHANGE_ME_generate_with_openssl_rand_hex_32
DEBUG=False
PORT=8000

# Database
DATABASE_URL=postgresql://user:password@localhost:5432/dbname
REDIS_URL=redis://localhost:6379/0

# Third-party APIs — get keys from the provider dashboard
STRIPE_SECRET_KEY=sk_test_YOUR_KEY_HERE
OPENAI_API_KEY=sk-proj-YOUR_KEY_HERE
AWS_ACCESS_KEY_ID=YOUR_AWS_KEY_HERE
AWS_SECRET_ACCESS_KEY=YOUR_AWS_SECRET_HERE

# Feature flags
ENABLE_FEATURE_X=False

Framework-Specific Rules

Next.js

• NEXT_PUBLIC_ prefix → inlined into browser bundle at build time (public, visible in DevTools)
• No prefix → server-only (never reaches the browser)
• Must exist at next build time, not just runtime. Pass to CI build step explicitly.

Vite

• VITE_ prefix → exposed to browser (import.meta.env.VITE_X)
• No prefix → build-scripts only, not bundled

Django

• Use django-environ or python-dotenv; never put real credentials in settings.py
• "False" is a truthy string — always parse booleans explicitly

Rust

• Use dotenvy for loading, config + secrecy::SecretString for type-safe production config
• Always .trim() before .parse() — trailing whitespace silently breaks type parsing

Docker / Docker Compose

• Use env_file: in compose, not environment: with inline values
• Never ENV SECRET_KEY=... in Dockerfile — it's visible in every layer and docker inspect
• Docker Compose resolves env_file paths relative to the Compose file location, not the CWD

The Boolean Trap (Extremely Common Bug)

# ❌ WRONG — the string "False" is truthy in Python
if os.getenv("DEBUG"):
    ...

# ✅ CORRECT
DEBUG = os.getenv("DEBUG", "False").lower() in ("true", "1", "yes")

// ❌ WRONG
let debug = std::env::var("DEBUG").unwrap_or("false".to_string());

// ✅ CORRECT — trim and compare
let debug = std::env::var("DEBUG")
    .unwrap_or_default()
    .trim()
    .to_lowercase() == "true";

Common Bugs Quick Reference

For detailed debugging patterns covering 10 frequent .env bugs (undefined variables, NEXT_PUBLIC in production, Docker path errors, boolean trap, Sentry leaks, Vite prefix, GitHub Actions masking, ALLOWED_HOSTS, Rust parse panics, silent teammate breakage), see references/debugging.md.

CI/CD — No .env Files Exist Here

In CI/CD pipelines, variables are injected from the platform's secret store. .env files should never be present.

# GitHub Actions — correct pattern
jobs:
  deploy:
    runs-on: ubuntu-latest
    env:
      DATABASE_URL: ${{ secrets.DATABASE_URL }}
      SECRET_KEY: ${{ secrets.DJANGO_SECRET_KEY }}

Enable GitHub Push Protection now: Settings → Code security → Push protection. Blocks 100+ secret patterns automatically. Free, takes 30 seconds. Do it before you forget.

Startup Validation — Fail Fast

Always validate required variables at startup, not at runtime when the missing variable is first used.

# Python — validate at import time
def validate_env():
    required = ["SECRET_KEY", "DATABASE_URL", "STRIPE_SECRET_KEY"]
    missing = [k for k in required if not os.getenv(k)]
    if missing:
        raise RuntimeError(f"Missing required env vars: {missing}")

validate_env()

// TypeScript / Node.js
const required = ["DATABASE_URL", "SECRET_KEY"] as const;
for (const key of required) {
  if (!process.env[key]) throw new Error(`Missing required env var: ${key}`);
}

Secret Managers — When to Graduate from .env

.env is for local development. For production, use a secrets manager.

Using evnx for Automated Validation

If evnx is available, use it for automated validation and secret scanning:

# Install evnx (choose your preferred method)
cargo install evnx                    # Rust/Cargo
npm install -g @evnx/cli              # Node.js/npm
pip install evnx                      # Python/pip

# Run validation and secret scanning
evnx validate --strict
evnx scan
evnx diff                             # Compare .env with .env.example

See the evnx-cli skill for the complete command reference and CI/CD integration patterns.

Further Reference

• references/format-spec.md — .env format grammar and edge cases
• references/security-checklist.md — full pre-deploy checklist
• references/debugging.md — 10 common bugs with fixes
• dotenv.space — complete multi-stack reference