Generators

Generator selection by outcome

Goal	Generator
Typed compile-time hints in code	ts / typescript
Runtime schema validation with Zod	zod
Drop-in env config for @t3-oss/env-nextjs	t3
Global process.env augmentation	declaration

Available generators and outputs

ts — TypeScript types

Produces a type Env declaration and ProcessEnv namespace augmentation:

// env.generated.typescript.ts
export type Env = {
  DATABASE_URL: string;
  PORT: number;
  DEBUG: boolean;
};

declare global {
  namespace NodeJS {
    interface ProcessEnv extends Env {}
  }
}

zod — Zod schema

Produces a Zod v4 schema split into server and client objects:

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

export const serverSchema = z.object({
  DATABASE_URL: z.string(),
  PORT: z.coerce.number(),
});

export const clientSchema = z.object({
  NEXT_PUBLIC_APP_URL: z.string().url(),
});

Variables prefixed with NEXT_PUBLIC_ are placed in clientSchema; all others go in serverSchema.

t3 — @t3-oss/env-nextjs

Produces a createEnv(...) call ready to drop into your project:

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

export const env = createEnv({
  server: {
    DATABASE_URL: z.string(),
  },
  client: {
    NEXT_PUBLIC_APP_URL: z.string().url(),
  },
  runtimeEnv: process.env,
});

declaration — Ambient .d.ts

Augments NodeJS.ProcessEnv with types for all declared variables:

// env.generated.d.ts
declare global {
  namespace NodeJS {
    interface ProcessEnv {
      DATABASE_URL: string;
      PORT: string;
    }
  }
}

Combining generators

Pass multiple --format flags to produce all outputs in one run:

env-typegen -i .env.example -o env.generated.ts -f ts -f zod -f t3 -f declaration

Recommended combos

• App runtime safety: -f zod -f declaration
• Full-stack TypeScript teams: -f ts -f zod -f declaration
• Next.js + @t3-oss/env-nextjs: -f t3 -f zod
• Migration path from ad-hoc env typing: start with -f ts, then add zod

FAQ

Is declaration enough without ts?

It augments process.env globally, but ts gives an explicit generated type that is often easier to import and test.

Can I skip t3 if I do not use Next.js?

Yes. t3 is optional and only needed if you want @t3-oss/env-nextjs output.