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, it's 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). 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
### <title> and <meta>
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="https://www.sitemaps.org/schemas/sitemap/0.9"
xmlns:xhtml="https://www.w3.org/1999/xhtml"
xmlns:mobile="https://www.google.com/schemas/sitemap-mobile/1.0"
xmlns:news="https://www.google.com/schemas/sitemap-news/0.9"
xmlns:image="https://www.google.com/schemas/sitemap-image/1.1"
xmlns:video="https://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.