Environment Management

Quick Guide: Per-app .env files. Framework-specific prefixes (NEXT_PUBLIC_* for Next.js, VITE_* for 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 - NEXT_PUBLIC_* 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, NEXT_PUBLIC_ 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 an external feature flag service)
• User-specific settings (use database or user preferences)
• Frequently changing values (use configuration API or database)
• Complex A/B testing with gradual rollouts (use a dedicated feature flag service)

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 (NEXT_PUBLIC_* 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.

---

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

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

Loading Order and Precedence

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

1. process.env (already set in environment)
2. .env.$(NODE_ENV).local (e.g., .env.production.local)
3. .env.local (not loaded when NODE_ENV=test)
4. .env.$(NODE_ENV) (e.g., .env.production)
5. .env

Vite loading order:

1. .env.[mode].local (e.g., .env.production.local)
2. .env.[mode] (e.g., .env.production)
3. .env.local
4. .env

Exception: Shared variables can go in your build tool's env configuration for cache invalidation

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. Define a schema, parse at startup, export a typed env object.

// lib/env.ts
const envSchema = z.object({
  VITE_API_URL: z.string().url(),
  VITE_API_TIMEOUT: z.coerce.number().default(DEFAULT_API_TIMEOUT_MS),
  VITE_ENABLE_ANALYTICS: z.stringbool().default(false), // Zod 4+ (NOT z.coerce.boolean())
});
export const env = envSchema.parse(import.meta.env);

Key gotchas:

• z.coerce.boolean() converts "false" to true (string is truthy) - always use z.stringbool() instead
• Use error.issues (not error.errors) for Zod 4 error handling

Note: For Next.js/Vite projects, consider T3 Env (@t3-oss/env-nextjs or @t3-oss/env-core) for 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

1. SCREAMING_SNAKE_CASE - All environment variables use uppercase with underscores
2. Descriptive names - Variable names clearly indicate purpose
3. 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

Core dependencies:

• Zod (v4+): Runtime validation and type inference for environment variables
• T3 Env (@t3-oss/env-nextjs, @t3-oss/env-core): Recommended wrapper for client/server separation

Framework support:

• Next.js: Automatic .env file loading with NEXT_PUBLIC_* prefix for client-side
• Vite: Automatic .env file loading with VITE_* prefix for client-side

Monorepo considerations:

• Declare shared env vars in your build tool's env configuration for cache invalidation
• Use per-app .env files even in monorepos to prevent conflicts

Replaces / Conflicts with:

• Hardcoded configuration values (use env vars instead)
• Runtime feature flag services for simple boolean flags (use env vars first, upgrade when needing gradual rollouts)

---

<decision_framework>

Decision Framework

See reference.md for complete decision frameworks including environment configuration and 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 NEXT_PUBLIC_* 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() (Zod 4+) instead
• Empty string env vars are NOT undefined - use T3 Env's emptyStringAsUndefined: true option
• Monorepo build tool caches may NOT be invalidated by env changes unless declared in the tool's env configuration

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

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

(You MUST use framework-specific prefixes for client-side variables - NEXT_PUBLIC_* 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)

Failure to follow these rules will cause runtime errors, security vulnerabilities, and configuration confusion.

</critical_reminders>