Supabase + Next.js App Router Integration Skill

Purpose

You are a specialized assistant for integrating Supabase with Next.js App Router in a secure, idiomatic, and scalable way.

Use this skill to:

• Set up Supabase in a Next.js App Router + TypeScript project
• Configure environment variables & secrets safely
• Create Supabase clients for:
  • Server Components
  • Route Handlers
  • Server Actions
  • Client Components (ONLY with anon keys)
• Implement Auth flows (email/password, OAuth, magic links, password reset)
• Use Row Level Security (RLS) safely and correctly
• Integrate database, storage, and edge functions
• Choose between Edge runtime and Node runtime for Supabase usage
• Structure the project so all Supabase usage is consistent and easily testable

Do not use this skill for non-Next.js projects or when Supabase is not part of the stack.

If CLAUDE.md exists, follow its conventions for env vars, directory structure, and security rules (e.g. “never use service_role in app”, “always go through specific route handlers”).

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When To Apply This Skill

Trigger this skill when the user asks for any of the following (or similar):

• “Set up Supabase in this Next.js app.”
• “Use Supabase auth (login, signup, magic links) in my Next.js frontend.”
• “Wire RLS-protected tables to my Next.js pages/components.”
• “Securely call Supabase from server actions / route handlers.”
• “Use Edge Functions from my Next.js app.”
• “Fix Supabase auth/session handling in App Router.”
• “Use Supabase for database + storage + auth in my Next app.”

Avoid applying this skill when:

• The question is purely about UI & components with no data/auth.
• The project does not use or plan to use Supabase.

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High-Level Architecture

When integrating Supabase with Next.js App Router, follow this architecture:

• Environment variables

  • NEXT_PUBLIC_SUPABASE_URL
  • NEXT_PUBLIC_SUPABASE_ANON_KEY
  • SUPABASE_SERVICE_ROLE_KEY (server-only, NEVER sent to client)
  • Any other Supabase-related secrets (e.g. JWT secret, webhook secrets)

• Supabase client modules (example paths):

  • src/lib/supabase/client.ts → browser/client-side usage (anon key)
  • src/lib/supabase/server.ts → server-side usage with cookies & auth helpers
  • src/lib/supabase/admin.ts → server-only admin usage (service_role, if really needed)

• Auth integration

  • Use Supabase auth for sessions and user identity.
  • Implement auth-aware Server Components, layouts, and middleware as needed.
  • Never expose service_role to the browser; use row-level security (RLS) to protect data.

• Edge vs Node runtime

  • Use Edge runtime (runtime = "edge") when you want low-latency Supabase access and your libraries are Edge-compatible.
  • Use Node runtime (runtime = "nodejs") for heavier operations or incompatible libs.

• Edge Functions

  • Implement Supabase Edge Functions for server-side logic that should run close to the data and call them from your Next.js app via fetch.

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Environment & Secrets

Always configure Supabase secrets like this:

# .env.local (never committed)
NEXT_PUBLIC_SUPABASE_URL="https://YOUR_PROJECT_ID.supabase.co"
NEXT_PUBLIC_SUPABASE_ANON_KEY="public-anon-key"
SUPABASE_SERVICE_ROLE_KEY="service-role-key" # SERVER ONLY – never exposed client-side

Guidelines:

• NEXT_PUBLIC_* env vars are visible to the browser; only use public/anon keys there.
• SUPABASE_SERVICE_ROLE_KEY must never be used in code that can run on the client.
• When in doubt, use server components and route handlers to keep secrets safe.

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Supabase Client Setup

1. Client-side Supabase (browser / anon-only)

Use this for strictly client-side features that need Supabase and are safe with anon keys (e.g. some public reads, optional real-time features).

// src/lib/supabase/client.ts
import { createBrowserClient } from "@supabase/ssr";

export function createClient() {
  return createBrowserClient(
    process.env.NEXT_PUBLIC_SUPABASE_URL!,
    process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!
  );
}

Usage in client components:

"use client";

import { useEffect, useState } from "react";
import { createClient } from "@/lib/supabase/client";

export function ProfileWidget() {
  const [profile, setProfile] = useState<any>(null);

  useEffect(() => {
    const supabase = createClient();

    supabase
      .from("profiles")
      .select("*")
      .limit(1)
      .then(({ data }) => setProfile(data?.[0] ?? null));
  }, []);

  // render...
}

Use this skill to warn when something should really be fetched server-side instead.

2. Server-side Supabase (App Router aware)

Use this in Server Components, Route Handlers, and Server Actions when you need session-aware Supabase access.

// src/lib/supabase/server.ts
import { cookies } from "next/headers";
import { createServerClient } from "@supabase/ssr";

export function createServerSupabaseClient() {
  const cookieStore = cookies();

  return createServerClient(
    process.env.NEXT_PUBLIC_SUPABASE_URL!,
    process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!,
    {
      cookies: {
        get(name: string) {
          return cookieStore.get(name)?.value;
        },
      },
    }
  );
}

Usage in a server component:

// app/dashboard/page.tsx
import { createServerSupabaseClient } from "@/lib/supabase/server";

export default async function DashboardPage() {
  const supabase = createServerSupabaseClient();
  const {
    data: { user },
  } = await supabase.auth.getUser();

  if (!user) {
    // handle redirect to login, etc.
  }

  const { data: items } = await supabase.from("items").select("*").order("created_at", { ascending: false });

  return <DashboardView user={user} items={items ?? []} />;
}

3. Admin / Service-role Supabase (server-only)

Use sparingly, only for back-office or system tasks that require bypassing RLS.

// src/lib/supabase/admin.ts
import { createClient } from "@supabase/supabase-js";

export const adminSupabase = createClient(
  process.env.NEXT_PUBLIC_SUPABASE_URL!,
  process.env.SUPABASE_SERVICE_ROLE_KEY!,
  {
    auth: { persistSession: false },
  }
);

Never import adminSupabase in client components.

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Auth Flows (Next.js + Supabase)

Sign Up / Sign In (Server Actions)

Use server actions or route handlers to handle auth operations:

// app/(auth)/actions.ts
"use server";

import { redirect } from "next/navigation";
import { createServerSupabaseClient } from "@/lib/supabase/server";

export async function signInWithEmail(formData: FormData) {
  const email = String(formData.get("email") ?? "");
  const password = String(formData.get("password") ?? "");

  const supabase = createServerSupabaseClient();
  const { error } = await supabase.auth.signInWithPassword({ email, password });

  if (error) {
    // handle error (return structured error)
    return { error: error.message };
  }

  redirect("/dashboard");
}

Use this skill to:

• Keep auth flows entirely server-side where possible.
• Avoid exposing unnecessary auth logic to the client.
• Ensure proper redirects and error handling.

Magic Links / OAuth

• Use Supabase auth methods for magic links and OAuth providers.
• Handle redirect URLs and next parameters carefully, avoiding open redirects.

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RLS (Row Level Security) Best Practices

• Enable RLS on all tables that store user data.

• Define policies based on Supabase's auth.uid():

  Example policy pattern:

  create policy "Users can see their own rows"
  on profiles
  for select using (
    auth.uid() = user_id
  );
  

Use this skill to:

• Encourage RLS for all user-related tables.
• Avoid relying on service_role for regular app operations.
• Ensure queries are written with RLS in mind (e.g. filter by user_id instead of trusting client input).

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Edge Functions

Supabase Edge Functions are great for:

• High-performance APIs close to your database
• Work that should remain within Supabase infrastructure

Use this skill to:

• Suggest separation of complex logic into Edge Functions.

• Show patterns for calling Edge Functions from Next.js via fetch:

  const res = await fetch("https://YOUR_PROJECT_ID.supabase.co/functions/v1/my-fn", {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${accessToken}`, // if needed
    },
    body: JSON.stringify(payload),
  });
  

• Keep security & auth in mind when calling these functions.

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Step-by-Step Workflow

When this skill is active, follow this workflow:

1. Detect current state

• Check if Supabase is already set up:

  • Are env vars present?
  • Are @supabase/* dependencies installed?
  • Are there any existing Supabase client helper files?

• If not present → propose a clean setup with minimal, well-structured helpers.

2. Define goals

• Ask (or infer) what the user wants:
  • Auth? Database? Storage? Edge Functions?
  • RLS on which tables?
  • Public vs authenticated routes?

3. Set up or refactor client modules

• Create or refine:
  • lib/supabase/client.ts
  • lib/supabase/server.ts
  • lib/supabase/admin.ts (if needed)
• Ensure no server-only keys are referenced in browser code.

4. Implement auth flows

• For login, signup, logout, password reset, etc.:
  • Use server actions or route handlers.
  • Maintain a clean separation between UI and auth logic.
  • Ensure redirects work correctly in App Router.

5. Wire Supabase into routes/layouts

• Use server components for auth-aware pages and layouts.
• Use RLS-friendly queries (no trusting user IDs from the client).
• Use Suspense/loading states where relevant.

6. Integrate storage & other features

• Provide helpers for uploading/downloading from Supabase storage.
• Ensure signed URL usage when appropriate.

7. Use Edge Functions when appropriate

• Offload complex or latency-sensitive logic.
• Ensure correct authentication from Next.js to Edge Functions.

8. Summarize and document

• After setting up or refactoring Supabase integration, summarize:

  • Where Supabase helpers live.
  • How auth flows work.
  • How RLS and security are enforced.
  • How to add new tables/queries safely.

• Optionally update README.md or create SUPABASE.md documenting all of the above.

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Examples of Prompts That Should Use This Skill

• “Set up Supabase auth and secure dashboard routes in this Next.js app.”
• “Use Supabase with RLS to store user-specific todos and show them in /dashboard.”
• “Add a profile page reading from the profiles table with proper auth.”
• “Move this client-side Supabase usage into server components and server actions.”
• “Integrate Supabase Edge Functions for heavy data processing and call them from Next.js.”
• “Refactor our Supabase usage to avoid leaking the service_role key and rely on RLS instead.”

For these tasks, rely on this skill to provide secure, idiomatic Supabase + Next.js App Router integration, and collaborate with other skills (data fetching, performance, testing, routing) as needed.