# Metadata

Add SEO metadata to Next.js pages using the Metadata API.

## Important: Server Components Only

The `metadata` object and `generateMetadata` function are **only supported in Server Components**. They cannot be used in Client Components.

If the target page has `'use client'`:

1. Remove `'use client'` if possible, move client logic to child components
2. Or extract metadata to a parent Server Component layout
3. Or split the file: Server Component with metadata imports Client Components

## Static Metadata

```tsx
import type { Metadata } from "next";

export const metadata: Metadata = {
  title: "Page Title",
  description: "Page description for search engines",
};
```

## Dynamic Metadata

```tsx
import type { Metadata } from "next";

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

export async function generateMetadata({ params }: Props): Promise<Metadata> {
  const { slug } = await params;
  const post = await getPost(slug);
  return { title: post.title, description: post.description };
}
```

## Avoid Duplicate Fetches

Use React `cache()` when the same data is needed for both metadata and page:

```tsx
import { cache } from "react";

export const getPost = cache(async (slug: string) => {
  return await db.posts.findFirst({ where: { slug } });
});
```

## Viewport

Separate from metadata for streaming support:

```tsx
import type { Viewport } from "next";

export const viewport: Viewport = {
  width: "device-width",
  initialScale: 1,
  themeColor: "#000000",
};

// Or dynamic
export function generateViewport({ params }): Viewport {
  return { themeColor: getThemeColor(params) };
}
```

## Title Templates

In root layout for consistent naming:

```tsx
export const metadata: Metadata = {
  title: { default: "Site Name", template: "%s | Site Name" },
};
```

## Metadata File Conventions

Reference: https://nextjs.org/docs/app/getting-started/project-structure#metadata-file-conventions

Place these files in `app/` directory (or route segments):

| File                            | Purpose                                       |
| ------------------------------- | --------------------------------------------- |
| `favicon.ico`                   | Favicon                                       |
| `icon.png` / `icon.svg`         | App icon                                      |
| `apple-icon.png`                | Apple app icon                                |
| `opengraph-image.png`           | OG image                                      |
| `twitter-image.png`             | Twitter card image                            |
| `sitemap.ts` / `sitemap.xml`    | Sitemap (use `generateSitemaps` for multiple) |
| `robots.ts` / `robots.txt`      | Robots directives                             |
| `manifest.ts` / `manifest.json` | Web app manifest                              |

## SEO Best Practice: Static Files Are Often Enough

For most sites, **static metadata files provide excellent SEO coverage**:

```
app/
├── favicon.ico
├── opengraph-image.png     # Works for both OG and Twitter
├── sitemap.ts
├── robots.ts
└── layout.tsx              # With title/description metadata
```

**Tips:**

- A single `opengraph-image.png` covers both Open Graph and Twitter (Twitter falls back to OG)
- Static `title` and `description` in layout metadata is sufficient for most pages
- Only use dynamic `generateMetadata` when content varies per page

---

# OG Image Generation

Generate dynamic Open Graph images using `next/og`.

## Important Rules

1. **Use `next/og`** - not `@vercel/og` (it's built into Next.js)
2. **No searchParams** - OG images can't access search params, use route params instead
3. **Avoid Edge runtime** - Use default Node.js runtime

```tsx
// Good
import { ImageResponse } from "next/og";

// Bad
// import { ImageResponse } from '@vercel/og'
// export const runtime = 'edge'
```

## Basic OG Image

```tsx
// app/opengraph-image.tsx
import { ImageResponse } from "next/og";

export const alt = "Site Name";
export const size = { width: 1200, height: 630 };
export const contentType = "image/png";

export default function Image() {
  return new ImageResponse(
    <div
      style={{
        fontSize: 128,
        background: "white",
        width: "100%",
        height: "100%",
        display: "flex",
        alignItems: "center",
        justifyContent: "center",
      }}
    >
      Hello World
    </div>,
    { ...size }
  );
}
```

## Dynamic OG Image

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

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

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

export default async function Image({ params }: Props) {
  const { slug } = await params;
  const post = await getPost(slug);

  return new ImageResponse(
    <div
      style={{
        fontSize: 48,
        background: "linear-gradient(to bottom, #1a1a1a, #333)",
        color: "white",
        width: "100%",
        height: "100%",
        display: "flex",
        flexDirection: "column",
        alignItems: "center",
        justifyContent: "center",
        padding: 48,
      }}
    >
      <div style={{ fontSize: 64, fontWeight: "bold" }}>{post.title}</div>
      <div style={{ marginTop: 24, opacity: 0.8 }}>{post.description}</div>
    </div>,
    { ...size }
  );
}
```

## Custom Fonts

```tsx
import { ImageResponse } from "next/og";
import { join } from "path";
import { readFile } from "fs/promises";

export default async function Image() {
  const fontPath = join(process.cwd(), "assets/fonts/Inter-Bold.ttf");
  const fontData = await readFile(fontPath);

  return new ImageResponse(
    <div style={{ fontFamily: "Inter", fontSize: 64 }}>Custom Font Text</div>,
    {
      width: 1200,
      height: 630,
      fonts: [{ name: "Inter", data: fontData, style: "normal" }],
    }
  );
}
```

## File Naming

- `opengraph-image.tsx` - Open Graph (Facebook, LinkedIn)
- `twitter-image.tsx` - Twitter/X cards (optional, falls back to OG)

## Styling Notes

ImageResponse uses Flexbox layout:

- Use `display: 'flex'`
- No CSS Grid support
- Styles must be inline objects

## Multiple OG Images

Use `generateImageMetadata` for multiple images per route:

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

export async function generateImageMetadata({ params }) {
  const images = await getPostImages(params.slug);
  return images.map((img, idx) => ({
    id: idx,
    alt: img.alt,
    size: { width: 1200, height: 630 },
    contentType: "image/png",
  }));
}

export default async function Image({ params, id }) {
  const images = await getPostImages(params.slug);
  const image = images[id];
  return new ImageResponse(/* ... */);
}
```

## Multiple Sitemaps

Use `generateSitemaps` for large sites:

```tsx
// app/sitemap.ts
import type { MetadataRoute } from "next";

export async function generateSitemaps() {
  // Return array of sitemap IDs
  return [{ id: 0 }, { id: 1 }, { id: 2 }];
}

export default async function sitemap({ id }: { id: number }): Promise<MetadataRoute.Sitemap> {
  const start = id * 50000;
  const end = start + 50000;
  const products = await getProducts(start, end);

  return products.map(product => ({
    url: `https://example.com/product/${product.id}`,
    lastModified: product.updatedAt,
  }));
}
```

Generates `/sitemap/0.xml`, `/sitemap/1.xml`, etc.
