Next.js SEO Optimization

Comprehensive SEO guide for Next.js App Router applications.

Quick SEO Audit

Run this checklist for any Next.js project:

1. Check robots.txt: curl https://your-site.com/robots.txt
2. Check sitemap: curl https://your-site.com/sitemap.xml
3. Check metadata: View page source, search for <title> and <meta name="description">
4. Check JSON-LD: View page source, search for application/ld+json
5. Check Core Web Vitals: Run Lighthouse in Chrome DevTools

Essential Files

app/layout.tsx - Root Metadata

import type { Metadata, Viewport } from 'next';

// Viewport must be a separate export — `themeColor`, `colorScheme`, and
// `viewport` inside the `metadata` object are not supported.
export const viewport: Viewport = {
  width: 'device-width',
  initialScale: 1,
  maximumScale: 5,
  userScalable: true,
  themeColor: [
    { media: '(prefers-color-scheme: light)', color: '#ffffff' },
    { media: '(prefers-color-scheme: dark)', color: '#0a0a0a' },
  ],
};

export const metadata: Metadata = {
  metadataBase: new URL('https://your-site.com'),
  title: {
    default: 'Site Title - Main Keyword',
    template: '%s | Site Name',
  },
  description: 'Compelling description with keywords (150-160 chars; Google typically displays this range)',
  keywords: ['keyword1', 'keyword2', 'keyword3'],
  openGraph: {
    type: 'website',
    locale: 'en_US',
    url: 'https://your-site.com',
    siteName: 'Site Name',
    title: 'Site Title',
    description: 'Description for social sharing',
    images: [{ url: '/og-image.png', width: 1200, height: 630, alt: 'Site preview' }],
  },
  twitter: {
    card: 'summary_large_image',
    title: 'Site Title',
    description: 'Description for Twitter',
    images: ['/og-image.png'],
  },
  alternates: {
    canonical: '/',
  },
  robots: {
    index: true,
    follow: true,
  },
};

app/sitemap.ts - Dynamic Sitemap

import type { MetadataRoute } from 'next';

export default function sitemap(): MetadataRoute.Sitemap {
  const baseUrl = 'https://your-site.com';

  return [
    {
      url: baseUrl,
      lastModified: new Date(),
      changeFrequency: 'weekly',
      priority: 1,
      images: [`${baseUrl}/og-image.png`], // Image Sitemap entry
    },
    {
      url: `${baseUrl}/about`,
      lastModified: new Date(),
      changeFrequency: 'monthly',
      priority: 0.8,
    },
  ];
}

app/robots.ts - Robots Configuration

import type { MetadataRoute } from 'next';

export default function robots(): MetadataRoute.Robots {
  const baseUrl = 'https://your-site.com';

  return {
    rules: [
      {
        userAgent: '*',
        allow: '/',
        disallow: ['/api/', '/admin/'],
        // Do NOT disallow /_next/ — crawlers need render-critical CSS/JS
        // Do NOT add bot-specific rules (Googlebot, Bingbot) unless overriding wildcard
      },
    ],
    sitemap: `${baseUrl}/sitemap.xml`,
    host: baseUrl,
  };
}

Key Principles

Cache Components & SEO

With cacheComponents: true in next.config.ts, use the "use cache" directive for SEO-critical server components:

// app/(home)/sections/hero-section.tsx
export async function HeroSection() {
  "use cache";
  cacheLife("minutes");   // Built-in profile: ~15 min
  cacheTag("hero");       // For targeted invalidation via revalidateTag("hero")

  const data = await fetchData();
  return <div>{/* SEO-visible content */}</div>;
}

Key rules:

• "use cache" must be the first statement in the function body
• No cookies()/headers() inside cache scope
• Use cacheLife() + cacheTag() instead of export const revalidate
• Sitemaps and metadata are static by default — only use "use cache" if they fetch dynamic data

Rendering Strategy for SEO

Core Web Vitals Targets

References

• Metadata API: See references/metadata-api.md
• Sitemap & Robots: See references/sitemap-robots.md
• JSON-LD Structured Data: See references/json-ld.md
• SEO Audit Checklist: See references/checklist.md
• Troubleshooting: See references/troubleshooting.md

Common Mistakes to Avoid

1. Mixing next-seo with Metadata API - Use only Metadata API in App Router
2. Missing canonical URLs - Always set alternates.canonical
3. Using CSR for SEO pages - Use SSG/SSR for indexable content
4. Blocking /_next/ in robots.txt - Crawlers need render-critical CSS/JS; never disallow /_next/
5. Missing metadataBase - Required for relative URLs in metadata
6. Viewport in metadata - Must be a separate export
7. Mixing metadata object and generateMetadata - Use one or the other, not both

Quick Fixes

Add noindex to a page

export const metadata: Metadata = {
  robots: {
    index: false,
    follow: false,
  },
};

Dynamic metadata per page

type Props = { params: Promise<{ id: string }> };

export async function generateMetadata({ params }: Props): Promise<Metadata> {
  const { id } = await params;            // params is a Promise in current Next.js
  const product = await getProduct(id);
  return {
    title: product.name,
    description: product.description,
  };
}

Canonical for dynamic routes

type Props = { params: Promise<{ slug: string }> };

export async function generateMetadata({ params }: Props): Promise<Metadata> {
  const { slug } = await params;
  return {
    alternates: {
      canonical: `/products/${slug}`,
    },
  };
}