# Migrate from Next.js — Replace NEXT_PUBLIC_* with Runtime Config

> Migrate from Next.js NEXT_PUBLIC_* build-time variables to REP runtime environment variables. Handles client-side code, SSR considerations, and automated codemod.

Source: https://rep-protocol.dev/guides/migration/from-next/

> **Caution**
>
> REP is designed for **client-side** environment variables. Next.js server-side `process.env.*` (without `NEXT_PUBLIC_` prefix) should remain as-is — they're already server-only and don't need REP.

## Automated migration

```bash
npx @rep-protocol/codemod --framework next src/
```

### What it transforms

```typescript
// Before
const apiUrl = process.env.NEXT_PUBLIC_API_URL;
const flags = process.env.NEXT_PUBLIC_FEATURE_FLAGS;

// After
import { rep } from '@rep-protocol/sdk';
const apiUrl = rep.get('API_URL');
const flags = rep.get('FEATURE_FLAGS');
```

Only `NEXT_PUBLIC_*` prefixed variables are transformed. Server-side `process.env.*` access is left unchanged.

### Preview first

```bash
npx @rep-protocol/codemod --framework next --dry-run src/
```

## Manual migration

1. **Rename environment variables:**
   ```bash
   NEXT_PUBLIC_API_URL        → REP_PUBLIC_API_URL
   NEXT_PUBLIC_ANALYTICS_KEY  → REP_SENSITIVE_ANALYTICS_KEY
   ```

2. **Update client-side code:**
   ```typescript
   import { rep } from '@rep-protocol/sdk';
   const apiUrl = rep.get('API_URL', 'http://localhost:3000');
   ```

3. **Install the SDK:**
   ```bash
   npm install @rep-protocol/sdk
   ```

## Post-migration cleanup

1. Remove `NEXT_PUBLIC_*` entries from `.env.local`, `.env.production`, etc.
2. Keep server-side `process.env.*` as-is (these are already server-only)
3. Run `rep typegen` for typed access
4. Update your Dockerfile to include the REP gateway

> **Note**
>
> For Next.js static export (`next export` or `output: 'export'`), REP works like any other SPA. For SSR deployments, REP handles only the client-side variables — server-side config continues to use standard Node.js `process.env`.