Nextjs15 Supabase

Cursor-Regel für Next.js 15 + Supabase — auf aktuelle App-Router-Konventionen zugeschnitten.

Original-Beschreibung der Autoren: 27 architecture rules preventing AI hallucinations: insecure auth (getSession vs getUser), synchronous params, deprecated imports, missing RLS, and Stripe key exposure. Built for Cursor Agent and Claude Code.

Die Regel

---
description: "27 architecture rules preventing AI hallucinations: insecure auth (getSession vs getUser), synchronous params, deprecated imports, missing RLS, and Stripe key exposure. Built for Cursor Agent and Claude Code."
globs: **/*
alwaysApply: false
---
# Next.js 15 + Supabase Architecture Rules

You are an expert Next.js 15 developer working with Supabase, TypeScript (strict), and shadcn/ui.
Follow ALL rules below unconditionally. If you are tempted to deviate, re-read the rule.

## Tech Stack
- Framework: Next.js 15 (App Router) with React 19
- Language: TypeScript (strict mode)
- Styling: Tailwind CSS + shadcn/ui
- Database: Supabase (PostgreSQL + RLS)
- Auth: Supabase SSR (cookie-based, @supabase/ssr)
- Validation: Zod
- Payments: Stripe (server-side only)

## RULE 1: NEVER use getSession() on the server

SECURITY CRITICAL. getSession() reads the JWT from cookies WITHOUT verifying it.
A forged cookie passes silently. ALWAYS use getUser() for server-side auth.

```typescript
// ✅ CORRECT — verified with Supabase auth server
const supabase = await createClient()
const { data: { user } } = await supabase.auth.getUser()
if (!user) redirect('/login')

// ❌ WRONG — reads JWT without verification, session can be forged
const { data: { session } } = await supabase.auth.getSession()

RULE 2: NEVER access params synchronously in Next.js 15

In Next.js 15, params and searchParams are Promises. Synchronous access compiles but crashes at runtime.

// ✅ CORRECT
export default async function Page({ params }: { params: Promise<{ id: string }> }) {
  const { id } = await params
}

// ❌ WRONG — runtime crash
export default function Page({ params }: { params: { id: string } }) {
  const { id } = params // TypeError at runtime
}

RULE 3: NEVER import from @supabase/auth-helpers-nextjs

This package is deprecated. It does NOT work with Next.js 15 App Router cookies. ALWAYS use @supabase/ssr with manual cookie handling.

// ✅ CORRECT
import { createServerClient } from '@supabase/ssr'

// ❌ WRONG — deprecated, broken with App Router
import { createServerComponentClient } from '@supabase/auth-helpers-nextjs'

RULE 4: All database tables MUST have RLS enabled

Every Supabase table must have Row Level Security enabled. Without RLS, any user with the anon key can read ALL data from the table.

-- ✅ Always add after CREATE TABLE:
ALTER TABLE public.my_table ENABLE ROW LEVEL SECURITY;

CREATE POLICY "Users can only read their own data"
  ON public.my_table FOR SELECT
  USING (auth.uid() = user_id);

RULE 5: Default to Server Components

Only add ‘use client’ when the component needs interactivity (event handlers, useState, useEffect). Push ‘use client’ to the smallest leaf component possible.

RULE 6: All mutations via Server Actions

All data mutations happen through Server Actions, never client-side fetch(). Always validate with Zod, authenticate with getUser(), and return ActionResponse.

'use server'
import { z } from 'zod'

type ActionResponse<T = void> =
  | { success: true; data: T }
  | { success: false; error: string }

const Schema = z.object({ title: z.string().min(1).max(200) })

export async function createItem(input: unknown): Promise<ActionResponse> {
  const supabase = await createClient()
  const { data: { user } } = await supabase.auth.getUser()
  if (!user) return { success: false, error: 'Unauthorized' }

  const result = Schema.safeParse(input)
  if (!result.success) return { success: false, error: 'Invalid input' }

  const { error } = await supabase.from('items').insert({ ...result.data, user_id: user.id })
  if (error) return { success: false, error: 'Failed to create item' }

  revalidatePath('/items')
  return { success: true, data: undefined }
}

RULE 7: Error boundaries for every data-fetching page

Every page that fetches data MUST have sibling loading.tsx and error.tsx files.

RULE 8: NEVER expose Stripe secret keys

Stripe keys starting with sk_ must NEVER be in NEXT_PUBLIC_ variables. Use process.env.STRIPE_SECRET_KEY (server-only).

RULE 9: TypeScript strict mode, no any

NEVER use any. Use unknown with Zod validation or type narrowing. tsconfig.json MUST have strict: true.

RULE 10: Middleware is for session REFRESH only

NEVER put auth enforcement in Next.js middleware. Middleware runs on Edge Runtime and cannot verify Supabase JWTs. Auth enforcement belongs in layouts/pages with getUser().

---

Full rule set (27 rules) available at: https://github.com/vibestackdev/vibe-stack Quick install: npx vibe-stack-rules init

## So nutzt du sie

Die Regel kopieren (Button oben) oder als Datei herunterladen und im Projekt unter `.cursor/rules/` ablegen — Cursor lädt sie beim nächsten Start automatisch. Ältere Cursor-Versionen lesen alternativ eine einzelne `.cursorrules`-Datei im Projektstamm; dort einfach den Regel-Text ohne den Kopfblock zwischen den `---`-Zeilen einfügen.

Der Regel-Text ist englisch — Cursor versteht ihn unabhängig von der Sprache, in der Sie mit dem Editor chatten.


## Im Detail

Speziell auf Next.js 15 zugeschnittene Regel in Kombination mit Supabase — berücksichtigt also aktuellere Next.js-Konzepte wie den App Router und asynchrone Request-APIs, statt veralteter Pages-Router-Muster. Relevant für alle, die auf der neuesten Next.js-Version starten und nicht riskieren wollen, dass die KI mit Konventionen älterer Next.js-Versionen arbeitet. Im Kern ähnlich zur allgemeinen Next.js-Vercel-Supabase-Regel, aber enger auf die Version 15 fokussiert — wer noch auf Next.js 13/14 setzt, ist mit der breiteren Variante besser bedient.

## Praxis-Tipp

Bei einem Fresh-Setup mit `create-next-app` (Version 15) direkt einbinden, bevor die erste Komponente entsteht, damit Cursor von Anfang an die richtigen Next-15-Patterns nutzt.

## Lizenz & Quelle

- **Lizenz:** CC0 1.0
- **Quelle:** [PatrickJS/awesome-cursorrules (GitHub)](https://github.com/PatrickJS/awesome-cursorrules)

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