T3 Env Validation

T3 Env Validation Skill

Type-safe environment variable validation with @t3-oss/env-nextjs and Zod.

Reference Files:

• setup.md - Configuration patterns
• schema-patterns.md - Common Zod validation patterns
• testing.md - Mocking env vars in tests
• examples.md - Practical examples

Project Configuration

Environment variables are validated in two files:

Quick Start

Adding Server Environment Variable

// data/env/server.ts
import { z } from "zod";
import { createEnv } from "@t3-oss/env-nextjs";

export const env = createEnv({
  server: {
    // Add new variable
    DATABASE_URL: z.string().url(),
    API_SECRET: z.string().min(32),
  },
  experimental__runtimeEnv: process.env,
  skipValidation: !!process.env.SKIP_ENV_VALIDATION,
  emptyStringAsUndefined: true,
});

Adding Client Environment Variable

// data/env/client.ts
import { z } from "zod";
import { createEnv } from "@t3-oss/env-nextjs";

export const env = createEnv({
  client: {
    // Must be prefixed with NEXT_PUBLIC_
    NEXT_PUBLIC_API_URL: z.string().url(),
  },
  // Must manually map client vars
  experimental__runtimeEnv: {
    NEXT_PUBLIC_API_URL: process.env.NEXT_PUBLIC_API_URL,
  },
  skipValidation: !!process.env.SKIP_ENV_VALIDATION,
  emptyStringAsUndefined: true,
});

Usage in Code

// Server-side (Server Components, Server Actions, API routes)
import { env } from "~/data/env/server";

const apiSecret = env.API_SECRET; // Type-safe!

// Client-side (Client Components)
import { env } from "~/data/env/client";

const apiUrl = env.NEXT_PUBLIC_API_URL; // Type-safe!

Key Concepts

Build-Time Validation

T3 Env validates environment variables at build time:

npm run build

❌ Invalid environment variables:
  CLERK_SECRET_KEY: Required
  FIREBASE_PROJECT_ID: Required

This prevents deploying with missing configuration.

Server vs Client Variables

Security Rule: Never put secrets in client variables!

Empty String Handling

emptyStringAsUndefined: true;

With this setting:

• VAR="" is treated as undefined
• Required vars with empty string will fail validation
• Optional vars with empty string use default

Common Patterns

Required String

API_KEY: z.string();

Optional with Default

LOG_LEVEL: z.enum(["debug", "info", "warn", "error"])
  .optional()
  .default("info");

Boolean Transform

FEATURE_FLAG: z.enum(["true", "false"])
  .optional()
  .transform((val) => val === "true");

URL Validation

API_URL: z.string().url();
DATABASE_URL: z.string().url().startsWith("postgresql://");

Number Transform

PORT: z.string().transform((val) => parseInt(val, 10));
TIMEOUT_MS: z.coerce.number().int().positive();

File Locations

Troubleshooting

Build Fails with Missing Env

# Skip validation (for Docker builds)
SKIP_ENV_VALIDATION=true npm run build

Variable Not Available

1. Server var → Can only be used in server code
2. Client var → Must be in experimental__runtimeEnv
3. Check spelling and NEXT_PUBLIC_ prefix

Type Errors

// Import from correct file
import { env } from "~/data/env/server"; // For server vars
import { env } from "~/data/env/client"; // For client vars

Related Skills

• server-actions - Using env vars in server actions
• firebase-firestore - Firebase env configuration
• clerk-auth-proxy - Clerk env configuration