# SEO

The most important aspect of SEO is to create high-quality content that is widely linked to from around the web. However, there are a few technical considerations for building sites that rank well.

## Out of the box

### SSR

While search engines have got better in recent years at indexing content that was rendered with client-side JavaScript, server-side rendered content is indexed more frequently and reliably. SvelteKit employs SSR by default, and while you can disable it in [`handle`](hooks#Server-hooks-handle), you should leave it on unless you have a good reason not to.

> [!NOTE] SvelteKit's rendering is highly configurable and you can implement [dynamic rendering](https://developers.google.com/search/docs/advanced/javascript/dynamic-rendering) if necessary. It's not generally recommended, since SSR has other benefits beyond SEO.

### Performance

Signals such as [Core Web Vitals](https://web.dev/vitals/#core-web-vitals) impact search engine ranking. Because Svelte and SvelteKit introduce minimal overhead, they make it easier to build high performance sites. You can test your site's performance using Google's [PageSpeed Insights](https://pagespeed.web.dev/) or [Lighthouse](https://developers.google.com/web/tools/lighthouse). With just a few key actions like using SvelteKit's default [hybrid rendering](glossary#Hybrid-app) mode and [optimizing your images](images), you can greatly improve your site's speed. Read [the performance page](performance) for more details.

### Normalized URLs

SvelteKit redirects pathnames with trailing slashes to ones without (or vice versa depending on your [configuration](page-options#trailingSlash)), as duplicate URLs are bad for SEO.

## Manual setup

### &lt;title&gt; and &lt;meta&gt;

Every page should have well-written and unique `<title>` and `<meta name="description">` elements inside a [`<svelte:head>`](../svelte/svelte-head). Guidance on how to write descriptive titles and descriptions, along with other suggestions on making content understandable by search engines, can be found on Google's [Lighthouse SEO audits](https://web.dev/lighthouse-seo/) documentation.

> [!NOTE] A common pattern is to return SEO-related `data` from page [`load`](load) functions, then use it (as [`page.data`]($app-state)) in a `<svelte:head>` in your root [layout](routing#layout).

### Sitemaps

[Sitemaps](https://developers.google.com/search/docs/advanced/sitemaps/build-sitemap) help search engines prioritize pages within your site, particularly when you have a large amount of content. You can create a sitemap dynamically using an endpoint:

```js
/// file: src/routes/sitemap.xml/+server.js
export async function GET() {
	return new Response(
		`
		<?xml version="1.0" encoding="UTF-8" ?>
		<urlset
			xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"
			xmlns:xhtml="http://www.w3.org/1999/xhtml"
			xmlns:mobile="http://www.google.com/schemas/sitemap-mobile/1.0"
			xmlns:news="http://www.google.com/schemas/sitemap-news/0.9"
			xmlns:image="http://www.google.com/schemas/sitemap-image/1.1"
			xmlns:video="http://www.google.com/schemas/sitemap-video/1.1"
		>
			<!-- <url> elements go here -->
		</urlset>`.trim(),
		{
			headers: {
				'Content-Type': 'application/xml'
			}
		}
	);
}
```

### AMP

An unfortunate reality of modern web development is that it is sometimes necessary to create an [Accelerated Mobile Pages (AMP)](https://amp.dev/) version of your site. In SvelteKit this can be done by setting the [`inlineStyleThreshold`](configuration#inlineStyleThreshold) option...

```js
/// file: svelte.config.js
/** @type {import('@sveltejs/kit').Config} */
const config = {
	kit: {
		// since <link rel="stylesheet"> isn't
		// allowed, inline all styles
		inlineStyleThreshold: Infinity
	}
};

export default config;
```

...disabling `csr` in your root `+layout.js`/`+layout.server.js`...

```js
/// file: src/routes/+layout.server.js
export const csr = false;
```

...adding `amp` to your `app.html`

```html
<html amp>
...
```

...and transforming the HTML using `transformPageChunk` along with `transform` imported from `@sveltejs/amp`:

```js
/// file: src/hooks.server.js
import * as amp from '@sveltejs/amp';

/** @type {import('@sveltejs/kit').Handle} */
export async function handle({ event, resolve }) {
	let buffer = '';
	return await resolve(event, {
		transformPageChunk: ({ html, done }) => {
			buffer += html;
			if (done) return amp.transform(buffer);
		}
	});
}
```

To prevent shipping any unused CSS as a result of transforming the page to amp, we can use [`dropcss`](https://www.npmjs.com/package/dropcss):

```js
// @filename: ambient.d.ts
declare module 'dropcss';

// @filename: index.js
// ---cut---
/// file: src/hooks.server.js
// @errors: 2307
import * as amp from '@sveltejs/amp';
import dropcss from 'dropcss';

/** @type {import('@sveltejs/kit').Handle} */
export async function handle({ event, resolve }) {
	let buffer = '';

	return await resolve(event, {
		transformPageChunk: ({ html, done }) => {
			buffer += html;

			if (done) {
				let css = '';
				const markup = amp
					.transform(buffer)
					.replace('⚡', 'amp') // dropcss can't handle this character
					.replace(/<style amp-custom([^>]*?)>([^]+?)<\/style>/, (match, attributes, contents) => {
						css = contents;
						return `<style amp-custom${attributes}></style>`;
					});

				css = dropcss({ css, html: markup }).css;
				return markup.replace('</style>', `${css}</style>`);
			}
		}
	});
}

```

> [!NOTE] It's a good idea to use the `handle` hook to validate the transformed HTML using `amphtml-validator`, but only if you're prerendering pages since it's very slow.