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SvelteKitBest practices

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, you should leave it on unless you have a good reason not to.

SvelteKit’s rendering is highly configurable and you can implement dynamic rendering if necessary. It’s not generally recommended, since SSR has other benefits beyond SEO.

Performance

Signals such as 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 or Lighthouse. Read the performance page for more details.

Normalized URLs

SvelteKit redirects pathnames with trailing slashes to ones without (or vice versa depending on your configuration), 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>. 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 documentation.

A common pattern is to return SEO-related data from page load functions, then use it (as $page.data) in a <svelte:head> in your root layout.

Sitemaps

Sitemaps 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:

src/routes/sitemap.xml/+server
export async function function GET(): Promise<Response>GET() {
	return new var Response: new (body?: BodyInit | null, init?: ResponseInit) => Response
This Fetch API interface represents the response to a request.


MDN Reference


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>`.String.trim(): string
Removes the leading and trailing white space and line terminator characters from a string.


trim(),
		{
			ResponseInit.headers?: HeadersInit | undefinedheaders: {
				'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) version of your site. In SvelteKit this can be done by setting the inlineStyleThreshold option...

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

export default 
const config: {
    kit: {
        inlineStyleThreshold: number;
    };
}
@type{import('@sveltejs/kit').Config}
config;

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

src/routes/+layout.server
export const const csr: falsecsr = false;

...adding amp to your app.html

<html amp>
...

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

src/hooks.server
import * as import ampamp from '@sveltejs/amp';

/** @type {import('@sveltejs/kit').Handle} */
export async function 
function handle({ event, resolve }: {
    event: any;
    resolve: any;
}): Promise<any>
@type{import('@sveltejs/kit').Handle}
handle({ event: anyevent, resolve: anyresolve }) {
	let let buffer: stringbuffer = '';
	return await resolve: anyresolve(event: anyevent, {
		
transformPageChunk: ({ html, done }: {
    html: any;
    done: any;
}) => string | undefined
transformPageChunk: ({ html: anyhtml, done: anydone }) => {
			let buffer: stringbuffer += html: anyhtml;
			if (done: anydone) return import ampamp.function transform(html: string): stringtransform(let buffer: stringbuffer);
		}
	});
}
import * as import ampamp from '@sveltejs/amp';
import type { 
type Handle = (input: {
    event: RequestEvent;
    resolve(event: RequestEvent, opts?: ResolveOptions): MaybePromise<Response>;
}) => MaybePromise<...>
The handle hook runs every time the SvelteKit server receives a request and
determines the response.
It receives an event object representing the request and a function called resolve, which renders the route and generates a Response.
This allows you to modify response headers or bodies, or bypass SvelteKit entirely (for implementing routes programmatically, for example).


Handle } from '@sveltejs/kit';

export const const handle: Handlehandle: 
type Handle = (input: {
    event: RequestEvent;
    resolve(event: RequestEvent, opts?: ResolveOptions): MaybePromise<Response>;
}) => MaybePromise<...>
The handle hook runs every time the SvelteKit server receives a request and
determines the response.
It receives an event object representing the request and a function called resolve, which renders the route and generates a Response.
This allows you to modify response headers or bodies, or bypass SvelteKit entirely (for implementing routes programmatically, for example).


Handle = async ({ event: RequestEvent<Partial<Record<string, string>>, string | null>event, resolve: (event: RequestEvent, opts?: ResolveOptions) => MaybePromise<Response>resolve }) => {
	let let buffer: stringbuffer = '';
	return await resolve: (event: RequestEvent, opts?: ResolveOptions) => MaybePromise<Response>resolve(event: RequestEvent<Partial<Record<string, string>>, string | null>event, {
		
ResolveOptions.transformPageChunk?(input: {
    html: string;
    done: boolean;
}): MaybePromise<string | undefined>
Applies custom transforms to HTML. If done is true, it’s the final chunk. Chunks are not guaranteed to be well-formed HTML
(they could include an element’s opening tag but not its closing tag, for example)
but they will always be split at sensible boundaries such as %sveltekit.head% or layout/page components.


@paraminput the html chunk and the info if this is the last chunk
transformPageChunk: ({ html: stringhtml, done: booleandone }) => {
			let buffer: stringbuffer += html: stringhtml;
			if (done: booleandone) return import ampamp.function transform(html: string): stringtransform(let buffer: stringbuffer);
		}
	});
};

To prevent shipping any unused CSS as a result of transforming the page to amp, we can use dropcss:

src/hooks.server
import * as import ampamp from '@sveltejs/amp';
import module "dropcss"dropcss from 'dropcss';

/** @type {import('@sveltejs/kit').Handle} */
export async function 
function handle(input: {
    event: RequestEvent;
    resolve(event: RequestEvent, opts?: ResolveOptions): MaybePromise<Response>;
}): MaybePromise<...>
@type{import('@sveltejs/kit').Handle}
handle({ event: RequestEvent<Partial<Record<string, string>>, string | null>event, resolve: (event: RequestEvent, opts?: ResolveOptions) => MaybePromise<Response>resolve }) {
	let let buffer: stringbuffer = '';

	return await resolve: (event: RequestEvent, opts?: ResolveOptions) => MaybePromise<Response>resolve(event: RequestEvent<Partial<Record<string, string>>, string | null>event, {
		
ResolveOptions.transformPageChunk?(input: {
    html: string;
    done: boolean;
}): MaybePromise<string | undefined>
Applies custom transforms to HTML. If done is true, it’s the final chunk. Chunks are not guaranteed to be well-formed HTML
(they could include an element’s opening tag but not its closing tag, for example)
but they will always be split at sensible boundaries such as %sveltekit.head% or layout/page components.


@paraminput the html chunk and the info if this is the last chunk
transformPageChunk: ({ html: stringhtml, done: booleandone }) => {
			let buffer: stringbuffer += html: stringhtml;

			if (done: booleandone) {
				let let css: stringcss = '';
				const const markup: stringmarkup = import ampamp
					.function transform(html: string): stringtransform(let buffer: stringbuffer)
					.String.replace(searchValue: string | RegExp, replaceValue: string): string (+3 overloads)
Replaces text in a string, using a regular expression or search string.


@paramsearchValue A string or regular expression to search for.
@paramreplaceValue A string containing the text to replace. When the {@linkcode searchValue} is a RegExp, all matches are replaced if the g flag is set (or only those matches at the beginning, if the y flag is also present). Otherwise, only the first match of {@linkcode searchValue} is replaced.
replace('⚡', 'amp') // dropcss can't handle this character
					.
String.replace(searchValue: {
    [Symbol.replace](string: string, replacer: (substring: string, ...args: any[]) => string): string;
}, replacer: (substring: string, ...args: any[]) => string): string (+3 overloads)
Replaces text in a string, using an object that supports replacement within a string.


@paramsearchValue A object can search for and replace matches within a string.
@paramreplacer A function that returns the replacement text.
replace(/<style amp-custom([^>]*?)>([^]+?)<\/style>/, (match: stringmatch, attributes: anyattributes, contents: anycontents) => {
						let css: stringcss = contents: anycontents;
						return `<style amp-custom${attributes: anyattributes}></style>`;
					});

				let css: stringcss = module "dropcss"dropcss({ css: stringcss, html: stringhtml: const markup: stringmarkup }).css;
				return const markup: stringmarkup.String.replace(searchValue: string | RegExp, replaceValue: string): string (+3 overloads)
Replaces text in a string, using a regular expression or search string.


@paramsearchValue A string or regular expression to search for.
@paramreplaceValue A string containing the text to replace. When the {@linkcode searchValue} is a RegExp, all matches are replaced if the g flag is set (or only those matches at the beginning, if the y flag is also present). Otherwise, only the first match of {@linkcode searchValue} is replaced.
replace('</style>', `${let css: stringcss}</style>`);
			}
		}
	});
}

import * as import ampamp from '@sveltejs/amp';
import module "dropcss"dropcss from 'dropcss';
import type { 
type Handle = (input: {
    event: RequestEvent;
    resolve(event: RequestEvent, opts?: ResolveOptions): MaybePromise<Response>;
}) => MaybePromise<...>
The handle hook runs every time the SvelteKit server receives a request and
determines the response.
It receives an event object representing the request and a function called resolve, which renders the route and generates a Response.
This allows you to modify response headers or bodies, or bypass SvelteKit entirely (for implementing routes programmatically, for example).


Handle } from '@sveltejs/kit';

export const const handle: Handlehandle: 
type Handle = (input: {
    event: RequestEvent;
    resolve(event: RequestEvent, opts?: ResolveOptions): MaybePromise<Response>;
}) => MaybePromise<...>
The handle hook runs every time the SvelteKit server receives a request and
determines the response.
It receives an event object representing the request and a function called resolve, which renders the route and generates a Response.
This allows you to modify response headers or bodies, or bypass SvelteKit entirely (for implementing routes programmatically, for example).


Handle = async ({ event: RequestEvent<Partial<Record<string, string>>, string | null>event, resolve: (event: RequestEvent, opts?: ResolveOptions) => MaybePromise<Response>resolve }) => {
	let let buffer: stringbuffer = '';

	return await resolve: (event: RequestEvent, opts?: ResolveOptions) => MaybePromise<Response>resolve(event: RequestEvent<Partial<Record<string, string>>, string | null>event, {
		
ResolveOptions.transformPageChunk?(input: {
    html: string;
    done: boolean;
}): MaybePromise<string | undefined>
Applies custom transforms to HTML. If done is true, it’s the final chunk. Chunks are not guaranteed to be well-formed HTML
(they could include an element’s opening tag but not its closing tag, for example)
but they will always be split at sensible boundaries such as %sveltekit.head% or layout/page components.


@paraminput the html chunk and the info if this is the last chunk
transformPageChunk: ({ html: stringhtml, done: booleandone }) => {
			let buffer: stringbuffer += html: stringhtml;

			if (done: booleandone) {
				let let css: stringcss = '';
				const const markup: stringmarkup = import ampamp
					.function transform(html: string): stringtransform(let buffer: stringbuffer)
					.String.replace(searchValue: string | RegExp, replaceValue: string): string (+3 overloads)
Replaces text in a string, using a regular expression or search string.


@paramsearchValue A string or regular expression to search for.
@paramreplaceValue A string containing the text to replace. When the {@linkcode searchValue} is a RegExp, all matches are replaced if the g flag is set (or only those matches at the beginning, if the y flag is also present). Otherwise, only the first match of {@linkcode searchValue} is replaced.
replace('⚡', 'amp') // dropcss can't handle this character
					.
String.replace(searchValue: {
    [Symbol.replace](string: string, replacer: (substring: string, ...args: any[]) => string): string;
}, replacer: (substring: string, ...args: any[]) => string): string (+3 overloads)
Replaces text in a string, using an object that supports replacement within a string.


@paramsearchValue A object can search for and replace matches within a string.
@paramreplacer A function that returns the replacement text.
replace(/<style amp-custom([^>]*?)>([^]+?)<\/style>/, (match: stringmatch, attributes: anyattributes, contents: anycontents) => {
						let css: stringcss = contents: anycontents;
						return `<style amp-custom${attributes: anyattributes}></style>`;
					});

				let css: stringcss = module "dropcss"dropcss({ css: stringcss, html: stringhtml: const markup: stringmarkup }).css;
				return const markup: stringmarkup.String.replace(searchValue: string | RegExp, replaceValue: string): string (+3 overloads)
Replaces text in a string, using a regular expression or search string.


@paramsearchValue A string or regular expression to search for.
@paramreplaceValue A string containing the text to replace. When the {@linkcode searchValue} is a RegExp, all matches are replaced if the g flag is set (or only those matches at the beginning, if the y flag is also present). Otherwise, only the first match of {@linkcode searchValue} is replaced.
replace('</style>', `${let css: stringcss}</style>`);
			}
		}
	});
};

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.

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