Agent Skills: Next.js SEO Optimization

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: Use PageSpeed Insights (pagespeed.web.dev) and the Search Console CWV report for field data — Lighthouse is lab-only and can't measure INP

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 was omitted intentionally — it's a non-standard directive Google ignores. Use canonical URLs / 301s to declare the preferred host instead. See references/sitemap-robots.md.

app/manifest.ts - Web App Manifest

import type { MetadataRoute } from 'next';

export default function manifest(): MetadataRoute.Manifest {
  return {
    name: 'Site Name',
    short_name: 'Site',
    description: 'Site description',
    start_url: '/',
    display: 'standalone',
    background_color: '#ffffff',
    theme_color: '#0a0a0a',
    icons: [
      { src: '/icon-192.png', sizes: '192x192', type: 'image/png' },
      { src: '/icon-512.png', sizes: '512x512', type: 'image/png' },
    ],
  };
}

Same MetadataRoute family as sitemap/robots; place at the root of app/. Minor for ranking, but expected for PWA completeness. (A static app/manifest.json works too.)

OG / Twitter Images

Three ways to set social images — prefer the file conventions over hand-syncing URLs in the metadata object:

1. External URL in metadata (the openGraph.images / twitter.images examples above) — fine for externally hosted images.
2. Static file convention (recommended default): drop opengraph-image.(png|jpg|gif) and/or twitter-image.* into a route segment (app/opengraph-image.png for the root, app/blog/opengraph-image.png for /blog). Next.js auto-emits og:image/twitter:image + :type/:width/:height. A deeper, more specific image overrides one above it. Add alt text with a sibling opengraph-image.alt.txt. Build fails if the file exceeds 8 MB (OG) / 5 MB (Twitter).
3. Dynamic generation with ImageResponse (per-page/per-post images):

// app/blog/[slug]/opengraph-image.tsx
import { ImageResponse } from 'next/og';

export const alt = 'Post preview';
export const size = { width: 1200, height: 630 };
export const contentType = 'image/png';

export default async function Image({ params }: { params: Promise<{ slug: string }> }) {
  const { slug } = await params;            // params is a Promise in v16
  const post = await getPost(slug);
  return new ImageResponse(
    <div style={{ display: 'flex', fontSize: 64, width: '100%', height: '100%' }}>{post.title}</div>,
    { ...size },
  );
}

ImageResponse renders via Satori — flexbox only, no display: grid. These files are statically optimized at build time unless they read request-time data. See references/metadata-api.md for fonts, generateImageMetadata, and the favicon/icon.tsx/apple-icon conventions.

Key Principles

Cache Components & SEO

With cacheComponents: true in next.config.ts (the v16 top-level flag that unifies the old experimental.dynamicIO/ppr/useCache), use the "use cache" directive for SEO-critical server components:

// app/(home)/sections/hero-section.tsx
import { cacheLife, cacheTag } from "next/cache";

export async function HeroSection() {
  "use cache";
  cacheLife("hours");   // SEO content that changes a few times/day; see profiles below
  cacheTag("hero");     // Invalidate via updateTag("hero") in a Server Action

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

Built-in cacheLife profiles (stale / revalidate / expire): seconds (30s/1s/1m), minutes (5m/1m/1h), hours (5m/1h/1d), days (5m/1d/1w), weeks (5m/1w/30d), max (5m/30d/1y), and the implicit default (5m/15m/never). For SEO pages pick by how often content changes — days for blog/docs, max for legal/marketing. (minutes revalidates every 1 min — too aggressive for most SEO content.)

Key rules:

• "use cache" must be the first statement in the function body (or at the top of the file for file-level caching)
• No cookies()/headers()/searchParams inside a plain "use cache" scope — good for SEO, since indexable content should be request-agnostic. ("use cache: private" does allow them, but is never prerendered, so it never lands in the static SEO shell.)
• Invalidate with updateTag("hero") inside a Server Action (read-your-writes), or revalidateTag("hero") from a Route Handler / webhook — prefer these over export const revalidate
• Short-lived caches (seconds, or revalidate < 5 min) are excluded from the prerender and become dynamic holes that need a <Suspense> boundary — keep SEO-critical content on a longer profile so it stays in the static shell
• Sitemaps and metadata are static by default — only add "use cache" (+ cacheTag) if they fetch CMS/dynamic data you want to invalidate on publish

Rendering Strategy for SEO

| Strategy | Use When | SEO Impact | |----------|----------|------------| | "use cache" | Server components with periodic data | Best - cached HTML, fast TTFB | | SSG (Static) | Content rarely changes | Best - pre-rendered HTML | | SSR | Dynamic content per request | Great - server-rendered | | CSR | Dashboards, authenticated areas | Poor - avoid for SEO pages |

Core Web Vitals Targets

| Metric | Target | Impact | |--------|--------|--------| | LCP (Largest Contentful Paint) | < 2.5s | Loading speed | | INP (Interaction to Next Paint) | < 200ms | Interactivity | | CLS (Cumulative Layout Shift) | < 0.1 | Visual stability |

• Measured on field data, not lab. Google ranks on the 75th percentile of real users (Chrome UX Report, 28-day rolling window, mobile/desktop separate). A URL group passes only when ≥75% of visits hit "Good" on all three. Use PageSpeed Insights and the Search Console CWV report for the real signal — Lighthouse is lab-only and cannot measure INP.
• INP replaced FID as a Core Web Vital on 2024-03-12; FID is deprecated. INP is the most commonly failed metric — prioritize it.
• Page experience is a tiebreaker, not a standalone ranking system (Google de-emphasized it). Good CWV won't rescue thin content; content relevance and quality come first. Treat CWV as baseline UX hygiene.
• Myths to ignore: 2026 SEO blogs falsely claim "LCP was lowered to 2.0s" and invent an "Engagement Reliability" metric. Neither exists in any Google/web.dev source — the thresholds above are current and unchanged since 2021.

Ranking Signals Beyond Technical SEO

Metadata + CWV alone don't drive rankings. Keep these in mind (out of scope for this skill, but pointers):

• Helpful content is part of core ranking (since 2024-03), evaluated continuously — not an episodic penalty.
• E-E-A-T (Experience, Expertise, Authoritativeness, Trust): cite real authors/credentials and first-hand experience, especially on YMYL pages.
• Mobile-first indexing is complete (since 2024-07): Google indexes the mobile rendering only. Ensure the mobile view has the same content, metadata, and structured data as desktop; never block mobile resources. (Mostly automatic with Next.js responsive design.)

References

• Metadata API: See references/metadata-api.md — generateMetadata, OG/icon file conventions, ImageResponse, manifest
• Sitemap & Robots: See references/sitemap-robots.md
• JSON-LD Structured Data: See references/json-ld.md
• AI Search (GEO/AEO) & AI Crawlers: See references/ai-search.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 in the same route segment
8. Duplicating icons in metadata + file conventions - Prefer favicon.ico/icon.*/opengraph-image.* file conventions; they auto-emit tags and override the metadata object
9. Blanket-blocking AI crawlers - GPTBot disallow: / blocks training but leaves you in AI search; don't accidentally block citation bots (OAI-SearchBot, PerplexityBot). See references/ai-search.md

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}`,
    },
  };
}