# Env Validation

> Environment variable validation — never raw process.env, Zod schema at startup, type-safe access

- Skill: `nadav011/env-validation` (Agent Skill)
- Install (CLI): `npx skillmds@latest add nadav011/env-validation`
- Raw SKILL.md: https://api.skillmd.com/api/skills/nadav011/env-validation/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: Nadav011 (https://skillmd.com/u/nadav011)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/nadav011/env-validation

---


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# Environment Variable Validation

---

## Core Rule

**NEVER use `process.env.X` directly.** Validate at startup with Zod.

```typescript
// ❌ WRONG — no types, fails at runtime
const apiUrl = process.env.API_URL            // possibly undefined
const port = parseInt(process.env.PORT || '')  // NaN if PORT="abc"

// ✅ CORRECT — validate once, typed access everywhere
import { env } from "@/lib/env"
const apiUrl = env.API_URL  // string — guaranteed at startup
const port = env.PORT       // number — parsed and validated
```

---

## Basic Pattern

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

const schema = z.object({
  DATABASE_URL:       z.string().url(),
  ANTHROPIC_API_KEY:  z.string().startsWith("sk-ant-"),
  STRIPE_SECRET_KEY:  z.string().startsWith("sk_"),
  NEXT_PUBLIC_APP_URL: z.string().url(),
  NODE_ENV:  z.enum(["development", "test", "production"]).default("development"),
  PORT:      z.coerce.number().int().min(1).max(65535).default(3000),
  LOG_LEVEL: z.enum(["debug", "info", "warn", "error"]).default("info"),
})

export const env = schema.parse(process.env)
```

`schema.parse(process.env)` runs once at module load — crashes immediately if any variable is missing or wrong type.

---

## t3-env (Next.js)

```typescript
import { createEnv } from "@t3-oss/env-nextjs"
import { z } from "zod"

export const env = createEnv({
  server: {
    DATABASE_URL:      z.string().url(),
    ANTHROPIC_API_KEY: z.string().min(1),
  },
  client: {
    NEXT_PUBLIC_APP_URL: z.string().url(),
  },
  runtimeEnv: {
    DATABASE_URL:        process.env.DATABASE_URL,
    ANTHROPIC_API_KEY:   process.env.ANTHROPIC_API_KEY,
    NEXT_PUBLIC_APP_URL: process.env.NEXT_PUBLIC_APP_URL,
  },
})

// Server code: env.DATABASE_URL         ✅
// Client code: env.NEXT_PUBLIC_APP_URL  ✅
// Client code: env.DATABASE_URL         ❌ TypeScript error!
```

---

## Validation Patterns

```typescript
ANTHROPIC_API_KEY: z.string().startsWith("sk-ant-")
GITHUB_TOKEN:      z.string().startsWith("ghp_")
FEATURE_FLAG:      z.string().transform(v => v === "true").pipe(z.boolean())
PORT:              z.coerce.number().int().positive().default(3000)
NODE_ENV:          z.enum(["development", "test", "production"])
```

---

## .env File Structure

```bash
# .env.example — COMMIT THIS (no real values)
DATABASE_URL=postgresql://localhost:5432/mydb
ANTHROPIC_API_KEY=sk-ant-...

# .env.local — NEVER COMMIT
DATABASE_URL=<real-value>
ANTHROPIC_API_KEY=<real-value>
```

**.gitignore must include:** `.env`, `.env.local`, `.env.*.local`, `*.env`

---

## CI Validation

```bash
node -e "require('./src/lib/env')"
```

Add to CI pipeline to catch missing secrets before deployment.