Next.js + shadcn/ui

Build distinctive, production-grade interfaces that avoid generic "AI slop" aesthetics.

Core Principles

1. Minimize noise - Icons communicate; excessive labels don't
2. No generic AI-UI - Avoid purple gradients, excessive shadows, predictable layouts
3. Context over decoration - Every element serves a purpose
4. Theme consistency - Use CSS variables from globals.css, never hardcode colors

Quick Start

bunx --bun shadcn@latest init -t next

For a custom design system, generate a preset code in shadcn/create and apply it:

bunx --bun shadcn@latest init --preset <CODE> --template next

Component Rules

Page Structure

// page.tsx - content only, no layout chrome
export default function Page() {
  return (
    <>
      <HeroSection />
      <Features />
      <Testimonials />
    </>
  );
}

// layout.tsx - shared UI (header, footer, sidebar)
export default function Layout({ children }: { children: React.ReactNode }) {
  return (
    <>
      <Header />
      <main>{children}</main>
      <Footer />
    </>
  );
}

Client Boundaries

• "use client" only at leaf components (smallest boundary)
• Props must be serializable (data or Server Actions, no functions/classes)
• Pass server content via children

Import Aliases

Always use @/ alias (e.g., @/lib/utils) instead of relative paths (../../lib/utils).

Style Merging

import { cn } from "@/lib/utils";

function Button({ className, ...props }) {
  return <button className={cn("px-4 py-2 rounded", className)} {...props} />;
}

File Organization

app/
├── (protected)/         # Auth required routes
│   ├── dashboard/
│   ├── settings/
│   ├── components/      # Route-specific components
│   └── lib/             # Route-specific utils/types
├── (public)/            # Public routes
│   ├── login/
│   └── register/
├── actions/             # Server Actions (global)
├── api/                 # API routes
├── layout.tsx           # Root layout
└── globals.css          # Theme tokens
components/              # Shared components
├── ui/                  # shadcn primitives
└── shared/              # Business components
hooks/                   # Custom React hooks
lib/                     # Shared utils
data/                    # Database queries
ai/                      # AI logic (tools, agents, prompts)

Next.js 16 Features

Async Params

export default async function Page({
  params,
  searchParams,
}: {
  params: Promise<{ id: string }>;
  searchParams: Promise<{ q?: string }>;
}) {
  const { id } = await params;
  const { q } = await searchParams;
}

Data Fetching vs Server Actions

CRITICAL RULE:

• Server Actions = ONLY for mutations (create, update, delete)
• Data fetching = In Server Components or 'use cache' functions

"use cache" (and cacheTag/cacheLife/updateTag) requires the Cache Components opt-in flag — Next.js 16 does not enable it by default:

// next.config.ts
const nextConfig = { cacheComponents: true }

// ❌ WRONG: Server Action for data fetching
"use server"
export async function getUsers() {
  return await db.users.findMany()
}

// ✅ CORRECT: Data function with caching
// data/users.ts
export async function getUsers() {
  "use cache"
  cacheTag("users")
  cacheLife("hours")
  return await db.users.findMany()
}

// ✅ CORRECT: Read cookies in Server Component directly
export default async function Page() {
  const theme = (await cookies()).get("theme")?.value ?? "light"
  return <App theme={theme} />
}

Caching

"use cache";

import { cacheTag, cacheLife } from "next/cache";

export async function getProducts() {
  cacheTag("products");
  cacheLife("hours");
  return await db.products.findMany();
}

Server Actions (Mutations Only)

"use server";

import { updateTag, revalidateTag } from "next/cache";
import { z } from "zod";

const schema = z.object({
  title: z.string().min(1),
  content: z.string(),
});

export async function createPost(formData: FormData) {
  // Always validate input
  const parsed = schema.parse({
    title: formData.get("title"),
    content: formData.get("content"),
  });

  await db.insert(posts).values(parsed);
  updateTag("posts"); // Read-your-writes
  // Or SWR-style revalidation: revalidateTag("posts", "max")
}

Proxy API

Use proxy.ts for request interception (replaces middleware). Place at project root:

// proxy.ts (project root, same level as app/)
import { NextResponse } from "next/server"
import type { NextRequest } from "next/server"

export function proxy(request: NextRequest) {
  // Auth checks, redirects, etc.
}

export const config = {
  matcher: ['/dashboard/:path*'],
}

Dev Tools (next-devtools-mcp)

Next.js 16+ ships an MCP endpoint at /_next/mcp that exposes the dev server's internals to coding agents. When working in a Next.js 16 project, recommend the user add next-devtools-mcp to .mcp.json:

{
  "mcpServers": {
    "next-devtools": {
      "command": "npx",
      "args": ["-y", "next-devtools-mcp@latest"]
    }
  }
}

Tools it provides (when dev server is running):

• get_errors — live build/runtime/type errors (esp. helpful for hydration mismatches)
• get_logs — dev log file path (browser console + server output)
• get_routes — all entry-point routes grouped by router type
• get_page_metadata — route, components, rendering details for a specific page
• get_project_metadata — project structure + dev server URL
• get_server_action_by_id — locate Server Action source from its hashed ID

Use these instead of asking the user to copy-paste error messages. Reference: nextjs.org/docs/app/guides/mcp.

References

• Architecture: references/architecture.md - Components, routing, Suspense, data patterns, AI directory structure
• Styling: references/styling.md - Themes, fonts, radius, animations, CSS variables
• Sidebar: references/sidebar.md - shadcn sidebar with nested layouts
• Project Setup: references/project-setup.md - bun commands, presets
• shadcn/ui: llms.txt - Official AI-optimized reference

Package Manager

Always use bun, never npm or npx:

• bun install (not npm install)
• bun add (not npm install package)
• bunx --bun (not npx)