nextjs-seo

What this skill does

# 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

```typescript
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

```typescript
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

```typescript
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](references/sitemap-robots.md).

### app/manifest.ts - Web App Manifest

```typescript
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):

```tsx
// 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](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:

```typescript
// 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-ren