Environment Management

Quick Guide: Per-app .env files (apps/client-next/.env). Framework-specific prefixes (NEXTPUBLIC_, VITE__). Zod validation at startup. Maintain .env.example templates. Never commit secrets (.gitignore). Environment-based feature flags.

<critical_requirements>

CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST validate ALL environment variables with Zod at application startup)

(You MUST use framework-specific prefixes for client-side variables - NEXTPUBLIC* for Next.js, VITE_* for Vite)

(You MUST maintain .env.example templates with ALL required variables documented)

(You MUST never commit secrets to version control - use .env.local and CI secrets)

(You MUST use per-app .env files - NOT root-level .env files)

</critical_requirements>

Auto-detection: Environment variables, .env files, Zod validation, t3-env, @t3-oss/env, secrets management, NEXTPUBLIC prefix, VITE_ prefix, feature flags, z.stringbool

When to use:

Setting up Zod validation for type-safe environment variables at startup
Managing per-app .env files with framework-specific prefixes
Securing secrets (never commit, use .env.local and CI secrets)
Implementing environment-based feature flags

When NOT to use:

Runtime configuration changes (use external feature flag services like LaunchDarkly)
User-specific settings (use database or user preferences)
Frequently changing values (use configuration API or database)
Complex A/B testing with gradual rollouts (use dedicated feature flag services)

Key patterns covered:

Per-app .env files (not root-level, prevents conflicts)
Zod validation at startup for type safety and early failure
T3 Env pattern for Next.js/Vite projects (recommended)
Framework-specific prefixes (NEXTPUBLIC_ for client, VITE__ for Vite client)
.env.example templates for documentation and onboarding

Detailed Resources:

For code examples, see examples/ folder:
- examples/core.md - Essential patterns (per-app .env, Zod validation)
- examples/t3-env.md - T3 Env pattern for Next.js/Vite (recommended)
- examples/naming-and-templates.md - Framework prefixes, .env.example
- examples/security-and-secrets.md - Secret management
- examples/feature-flags-and-config.md - Feature flags, centralized config
For decision frameworks and anti-patterns, see reference.md

Philosophy

Environment management follows the principle that configuration is code - it should be validated, typed, and versioned. The system uses per-app .env files with framework-specific prefixes, Zod validation at startup, and strict security practices to prevent secret exposure.

When to use this environment management approach:

Managing environment-specific configuration (API URLs, feature flags, credentials)
Setting up type-safe environment variables with Zod validation
Securing secrets with .gitignore and CI/CD secret management
Implementing feature flags without external services
Documenting required environment variables for team onboarding

When NOT to use:

Runtime configuration changes (use external feature flag services like LaunchDarkly)
User-specific settings (use database or user preferences)
Frequently changing values (use configuration API or database)

Core Patterns

Pattern 1: Per-App Environment Files

Each app/package has its own .env file to prevent conflicts and clarify ownership.

File Structure

apps/
├── client-next/
│   ├── .env                    # Local development (NEXT_PUBLIC_API_URL)
│   └── .env.production         # Production overrides
├── client-react/
│   ├── .env                    # Local development
│   └── .env.production         # Production overrides
└── server/
    ├── .env                    # Local server config
    ├── .env.example            # Template for new developers
    └── .env.local.example      # Local overrides template

packages/
├── api/
│   └── .env                    # API package config
└── api-mocks/
    └── .env                    # Mock server config

File Types and Purpose

.env - Default development values (committed for apps, gitignored for sensitive packages)
.env.example - Documentation template (committed, shows all required variables)
.env.local - Local developer overrides (gitignored, takes precedence over .env)
.env.production - Production configuration (committed or in CI secrets)
.env.local.example - Local override template (committed)

Loading Order and Precedence

Next.js loading order (highest to lowest priority):

.env.$(NODE_ENV).local (e.g., .env.production.local)
.env.local (not loaded when NODE_ENV=test)
.env.$(NODE_ENV) (e.g., .env.production)
.env

Vite loading order:

.env.[mode].local (e.g., .env.production.local)
.env.[mode] (e.g., .env.production)
.env.local
.env

Exception: Shared variables can go in turbo.json env array (see setup/monorepo/basic.md)

See examples/core.md for complete code examples.

Pattern 2: Type-Safe Environment Variables with Zod

Validate environment variables at application startup using Zod schemas.

Constants

const DEFAULT_API_TIMEOUT_MS = 30000;
const DEFAULT_API_RETRY_ATTEMPTS = 3;

Validation Schema

// lib/env.ts
import { z } from "zod";

const DEFAULT_API_TIMEOUT_MS = 30000;

const envSchema = z.object({
  // Public variables (VITE_ prefix)
  VITE_API_URL: z.string().url(),
  VITE_API_TIMEOUT: z.coerce.number().default(DEFAULT_API_TIMEOUT_MS),
  // Use z.stringbool() for boolean env vars (Zod 4+)
  // Handles "true"/"false"/"1"/"0"/"yes"/"no" correctly
  VITE_ENABLE_ANALYTICS: z.stringbool().default(false),
  VITE_ENVIRONMENT: z.enum(["development", "staging", "production"]),

  // Build-time variables
  MODE: z.enum(["development", "production"]),
  DEV: z.boolean(),
  PROD: z.boolean(),
});

// Validate and export
function validateEnv() {
  try {
    return envSchema.parse(import.meta.env);
  } catch (error) {
    if (error instanceof z.ZodError) {
      console.error("Invalid environment variables:");
      error.errors.forEach((err) => {
        console.error(`  - ${err.path.join(".")}: ${err.message}`);
      });
      throw new Error("Invalid environment configuration");
    }
    throw error;
  }
}

export const env = validateEnv();

// Type-safe usage
console.log(env.VITE_API_URL); // string
console.log(env.VITE_API_TIMEOUT); // number
console.log(env.VITE_ENABLE_ANALYTICS); // boolean

Why good: Type safety prevents runtime errors from typos or wrong types, runtime validation fails fast at startup with clear error messages, default values reduce required configuration, IDE autocomplete improves DX

Note: For Next.js/Vite projects, consider using T3 Env (@t3-oss/env-nextjs or @t3-oss/env-core) which provides additional features like client/server variable separation and build-time validation. See examples/t3-env.md.

See examples/core.md for complete good/bad comparisons.

Pattern 3: Framework-Specific Naming Conventions

Use framework-specific prefixes for client-side variables and SCREAMING_SNAKE_CASE for all environment variables.

Mandatory Conventions

SCREAMING_SNAKE_CASE - All environment variables use uppercase with underscores
Descriptive names - Variable names clearly indicate purpose
Framework prefixes - Use NEXT_PUBLIC_* (Next.js) or VITE_* (Vite) for client-side variables

Framework Prefixes

Next.js:

NEXT_PUBLIC_* - Client-side accessible (embedded in bundle) - use for API URLs, public keys, feature flags
No prefix - Server-side only (database URLs, secret keys, API tokens)

Vite:

VITE_* - Client-side accessible (embedded in bundle) - use for API URLs, public configuration
No prefix - Build-time only (not exposed to client)

Node.js/Server:

NODE_ENV - Standard environment (development, production, test)
PORT - Server port number
No prefix - All variables available server-side

See examples/naming-and-templates.md for complete code examples with good/bad comparisons.

Integration Guide

Works with:

Zod: Runtime validation and type inference for environment variables
T3 Env: Recommended wrapper for Zod validation with client/server separation (@t3-oss/env-nextjs, @t3-oss/env-core)
Turborepo: Declare shared env vars in turbo.json for cache invalidation (see setup/monorepo/basic.md)
CI/CD: GitHub Secrets, Vercel Environment Variables for production secrets (see backend/ci-cd/basic.md)
Next.js: Automatic .env file loading with NEXTPUBLIC* prefix for client-side
Vite: Automatic .env file loading with VITE_* prefix for client-side

Replaces / Conflicts with:

Hardcoded configuration values (use env vars instead)
Runtime feature flag services for simple boolean flags (use env vars first, upgrade to LaunchDarkly if needed)

<decision_framework>

Decision Framework

Need environment configuration?
├─ Is it a secret (API key, password)?
│   ├─ YES → Use .env.local (gitignored) + CI secrets
│   └─ NO → Can it be public (embedded in client bundle)?
│       ├─ YES → Use NEXT_PUBLIC_* or VITE_* prefix
│       └─ NO → Server-side only (no prefix)
├─ Does it change per environment?
│   ├─ YES → Use .env.{environment} files
│   └─ NO → Use .env with defaults
└─ Is it app-specific or shared?
    ├─ App-specific → Per-app .env file
    └─ Shared → Declare in turbo.json env array

See reference.md for complete decision frameworks including feature flag decisions.

</decision_framework>

<red_flags>

RED FLAGS

High Priority Issues:

Committing secrets to version control (.env files with real credentials)
Using environment variables directly without Zod validation (causes runtime errors)
Using NEXTPUBLIC_ or VITE__ prefix for secrets (embeds in client bundle)

Medium Priority Issues:

Missing .env.example documentation (poor onboarding experience)
Using production secrets in development (security risk)
Root-level .env in monorepo (causes conflicts)

Gotchas:

Next.js/Vite embed prefixed variables at build time, not runtime - requires rebuild to change
Environment variables are strings - use z.coerce.number() for numbers, use z.stringbool() for booleans (Zod 4+)
CRITICAL: z.coerce.boolean() converts "false" to true (string is truthy) - use z.stringbool() instead
Empty string env vars are NOT undefined - use T3 Env's emptyStringAsUndefined: true option
Turborepo cache is NOT invalidated by env changes unless declared in turbo.json env array

See reference.md for complete RED FLAGS, anti-patterns, and checklists.

</red_flags>

<critical_reminders>

CRITICAL REMINDERS

All code must follow project conventions in CLAUDE.md