SvelteKitBuild and deploy

Cloudflare

To deploy to Cloudflare Workers, use adapter-cloudflare.

This adapter will be installed by default when you use adapter-auto. If you plan on staying with Cloudflare, you can switch from adapter-auto to using this adapter directly so that cloudflare:workers is emulated during local development, type declarations are automatically applied, and the ability to set Cloudflare-specific options is provided.

Comparisons

adapter-cloudflare – supports all SvelteKit features; builds for Cloudflare Workers Static Assets
adapter-cloudflare-workers – deprecated. Supports all SvelteKit features; builds for Cloudflare Workers Sites
adapter-static – only produces client-side static assets; compatible with Cloudflare Workers Static Assets and Cloudflare Pages

Usage

Run npx sv add sveltekit-adapter="adapter:cloudflare", or install with npm i -D @sveltejs/adapter-cloudflare and add the adapter to your vite.config.js:

vite.config

import adapter(alias) function adapter(options?: AdapterOptions): Adapter
import adapter from '@sveltejs/adapter-cloudflare';
import { sveltekit(alias) function sveltekit(config?: Config): Promise<Plugin[]>
import sveltekitThe SvelteKit Vite plugin, which must be added to your vite.config.js file along with your project's configuration:
/// file: vite.config.js
import adapter from '@sveltejs/adapter-auto';
import { sveltekit } from '@sveltejs/kit/vite';
import { defineConfig } from 'vite';

export default defineConfig({
	plugins: [
		sveltekit({
			adapter: adapter(),
			compilerOptions: {
				experimental: {
					async: true
				}
			},
			experimental: {
				remoteFunctions: true
			}
		})
	]
});
As well as SvelteKit, the plugin options are used by other tooling that integrates with Svelte such as editor extensions.
Any options that don't belong to SvelteKit are passed through to vite-plugin-svelte, so you can set options like inspector here too. The experimental namespace is shared — SvelteKit reads its own flags and forwards the rest.

[!LEGACY]
Prior to SvelteKit 3, config lived in a svelte.config.js file, which is no longer supported. The ability to configure SvelteKit via vite.config.js was added in version 2.62.

reference } from '@sveltejs/kit/vite';
import { defineConfig(alias) function defineConfig(config: UserConfig): UserConfig (+5 overloads)
import defineConfigType helper to make it easier to use vite.config.ts
accepts a direct 
{@link 
UserConfig
}
 object, or a function that returns it.
The function receives a 
{@link 
ConfigEnv
}
 object.
 } from 'vite';

export default defineConfig(alias) defineConfig(config: UserConfig): UserConfig (+5 overloads)
import defineConfigType helper to make it easier to use vite.config.ts
accepts a direct 
{@link 
UserConfig
}
 object, or a function that returns it.
The function receives a 
{@link 
ConfigEnv
}
 object.
({
	plugins(property) UserConfig.plugins?: PluginOption[] | undefinedArray of vite plugins to use.
: [
		sveltekit(alias) sveltekit(config?: Config): Promise<Plugin[]>
import sveltekitThe SvelteKit Vite plugin, which must be added to your vite.config.js file along with your project's configuration:
/// file: vite.config.js
import adapter from '@sveltejs/adapter-auto';
import { sveltekit } from '@sveltejs/kit/vite';
import { defineConfig } from 'vite';

export default defineConfig({
	plugins: [
		sveltekit({
			adapter: adapter(),
			compilerOptions: {
				experimental: {
					async: true
				}
			},
			experimental: {
				remoteFunctions: true
			}
		})
	]
});
As well as SvelteKit, the plugin options are used by other tooling that integrates with Svelte such as editor extensions.
Any options that don't belong to SvelteKit are passed through to vite-plugin-svelte, so you can set options like inspector here too. The experimental namespace is shared — SvelteKit reads its own flags and forwards the rest.

[!LEGACY]
Prior to SvelteKit 3, config lived in a svelte.config.js file, which is no longer supported. The ability to configure SvelteKit via vite.config.js was added in version 2.62.

reference({
			adapter(property) Config.adapter?: Adapter | undefinedYour adapter is run when executing vite build. It determines how the output is converted for different platforms.
undefined
: adapter(alias) adapter(options?: AdapterOptions): Adapter
import adapter({
				// See below for an explanation of these options
				config(property) AdapterOptions.config?: string | undefinedPath to your Wrangler configuration file.
: undefinedvar undefined,
				platformProxy(property) AdapterOptions.platformProxy?: GetPlatformProxyOptions | undefinedConfig object passed to getPlatformProxy
during development and preview.
: {
					configPath(property) configPath?: string | undefinedThe path to the config file to use.
If no path is specified the default behavior is to search from the
current directory up the filesystem for a Wrangler configuration file to use.
Note: this field is optional but if a path is specified it must
      point to a valid file on the filesystem
: undefinedvar undefined,
					environment(property) environment?: string | undefinedThe name of the environment to use
: undefinedvar undefined,
					persist(property) persist?: boolean | {
    path: string;
} | undefinedIndicates if and where to persist the bindings data, if not present or true it defaults to the same location
used by wrangler: .wrangler/state/v3 (so that the same data can be easily used by the caller and wrangler).
If false is specified no data is persisted on the filesystem.
: undefinedvar undefined
				},
				fallback(property) AdapterOptions.fallback?: "plaintext" | "spa" | undefinedWhether to render a plaintext 404.html page or a rendered SPA fallback page
for non-matching asset requests.
For Cloudflare Workers, the default behaviour is to return a null-body
404-status response for non-matching assets requests. However, if the
assets.not_found_handling
Wrangler configuration setting is set to "404-page", this page will be
served if a request fails to match an asset. If assets.not_found_handling
is set to "single-page-application", the adapter will render a SPA fallback
index.html page regardless of the fallback option specified.
'plaintext'
: 'plaintext'
			})
		})
	]
});

Options

config

Path to your Wrangler configuration file. If you would like to use a Wrangler configuration filename other than wrangler.jsonc, wrangler.json, or wrangler.toml you can specify it using this option.

platformProxy

Preferences for the emulated env local bindings. See the getPlatformProxy Wrangler API documentation for a full list of options.

fallback

Whether to render a plaintext 404.html page or a rendered SPA fallback page for non-matching asset requests.

For Cloudflare Workers, the default behaviour is to return a null-body 404-status response for non-matching assets requests. However, if the assets.not_found_handling Wrangler configuration setting is set to "404-page", this page will be served if a request fails to match an asset. If assets.not_found_handling is set to "single-page-application", the adapter will render a SPA fallback index.html page regardless of the fallback option specified.

Basic configuration

The adapter expects to find a Wrangler configuration file in the project root. It should look something like this:

wrangler

{
	"name": "<any-name-you-want>",
	"main": ".svelte-kit/cloudflare/_worker.js",
	"compatibility_flags": ["nodejs_als"],
	"compatibility_date": "<YYYY-MM-DD>",
	"assets": {
		"binding": "ASSETS",
		"directory": ".svelte-kit/cloudflare",
	}
}

Deployment

You can use the Wrangler CLI to deploy your application by running npx wrangler deploy or use the Cloudflare Git integration to enable automatic builds and deployments on push.

Runtime APIs

The env object contains your project’s bindings, which consist of KV/DO namespaces, etc. It is available on the cloudflare:workers module.

+server

import { env } from 'cloudflare:workers';

/** @type {import('./$types').RequestHandler} */
export async function POST() {
	const x = env.YOUR_DURABLE_OBJECT_NAMESPACE.idFromName('x');
}

import { env } from 'cloudflare:workers';
import type { RequestHandler } from './$types';

export const POST: RequestHandler = async () => {
	const x = env.YOUR_DURABLE_OBJECT_NAMESPACE.idFromName('x');
};

SvelteKit’s built-in $app/env/* modules should be preferred for environment variables.

To make these types available to your app, install wrangler and run wrangler types.

Testing locally

Cloudflare specific values are emulated during dev and preview modes. Local bindings are created based on your Wrangler configuration file and are used to populate env during development and preview. Use the adapter config platformProxy option to change your preferences for the bindings.

Durable Objects and Workflows, which require custom classes to be exported from your worker, are not currently supported.

For testing the build, you should use Wrangler version 4. Once you have built your site, run wrangler dev.

Headers and redirects

The _headers and _redirects files, specific to Cloudflare, can be used for static asset responses (like images) by putting them into the project root folder.

However, they will have no effect on responses dynamically rendered by SvelteKit, which should return custom headers or redirect responses from server endpoints or with the handle hook.

Troubleshooting

Node.js compatibility

If you would like to enable Node.js compatibility, you can add the nodejs_compat compatibility flag to your Wrangler configuration file:

wrangler

{
	"compatibility_flags": ["nodejs_compat"]
}

Worker size limits

When deploying your application, the server generated by SvelteKit is bundled into a single file. Wrangler will fail to publish your worker if it exceeds the size limits after minification. You’re unlikely to hit this limit usually, but some large libraries can cause this to happen. In that case, you can try to reduce the size of your worker by only importing such libraries on the client side. See the FAQ for more information.

Accessing the file system

You can’t use fs in Cloudflare Workers.

Instead, use the read function from $app/server to access your files. It works by fetching the file from the deployed public assets location.

Alternatively, you can prerender the routes in question.

Migrating from Workers Sites

Cloudflare no longer recommends using Workers Sites and instead recommends using Workers Static Assets. To migrate, replace @sveltejs/adapter-cloudflare-workers with @sveltejs/adapter-cloudflare and remove all site configuration settings from your Wrangler configuration file, then add the assets.directory and assets.binding configuration settings:

vite.config

import adapter(alias) function adapter(options?: AdapterOptions): Adapter
import adapter from '@sveltejs/adapter-cloudflare';
import { sveltekit(alias) function sveltekit(config?: Config): Promise<Plugin[]>
import sveltekitThe SvelteKit Vite plugin, which must be added to your vite.config.js file along with your project's configuration:
/// file: vite.config.js
import adapter from '@sveltejs/adapter-auto';
import { sveltekit } from '@sveltejs/kit/vite';
import { defineConfig } from 'vite';

export default defineConfig({
	plugins: [
		sveltekit({
			adapter: adapter(),
			compilerOptions: {
				experimental: {
					async: true
				}
			},
			experimental: {
				remoteFunctions: true
			}
		})
	]
});
As well as SvelteKit, the plugin options are used by other tooling that integrates with Svelte such as editor extensions.
Any options that don't belong to SvelteKit are passed through to vite-plugin-svelte, so you can set options like inspector here too. The experimental namespace is shared — SvelteKit reads its own flags and forwards the rest.

[!LEGACY]
Prior to SvelteKit 3, config lived in a svelte.config.js file, which is no longer supported. The ability to configure SvelteKit via vite.config.js was added in version 2.62.

reference } from '@sveltejs/kit/vite';
import { defineConfig(alias) function defineConfig(config: UserConfig): UserConfig (+5 overloads)
import defineConfigType helper to make it easier to use vite.config.ts
accepts a direct 
{@link 
UserConfig
}
 object, or a function that returns it.
The function receives a 
{@link 
ConfigEnv
}
 object.
 } from 'vite';

export default defineConfig(alias) defineConfig(config: UserConfig): UserConfig (+5 overloads)
import defineConfigType helper to make it easier to use vite.config.ts
accepts a direct 
{@link 
UserConfig
}
 object, or a function that returns it.
The function receives a 
{@link 
ConfigEnv
}
 object.
({
	plugins(property) UserConfig.plugins?: PluginOption[] | undefinedArray of vite plugins to use.
: [
		sveltekit(alias) sveltekit(config?: Config): Promise<Plugin[]>
import sveltekitThe SvelteKit Vite plugin, which must be added to your vite.config.js file along with your project's configuration:
/// file: vite.config.js
import adapter from '@sveltejs/adapter-auto';
import { sveltekit } from '@sveltejs/kit/vite';
import { defineConfig } from 'vite';

export default defineConfig({
	plugins: [
		sveltekit({
			adapter: adapter(),
			compilerOptions: {
				experimental: {
					async: true
				}
			},
			experimental: {
				remoteFunctions: true
			}
		})
	]
});
As well as SvelteKit, the plugin options are used by other tooling that integrates with Svelte such as editor extensions.
Any options that don't belong to SvelteKit are passed through to vite-plugin-svelte, so you can set options like inspector here too. The experimental namespace is shared — SvelteKit reads its own flags and forwards the rest.

[!LEGACY]
Prior to SvelteKit 3, config lived in a svelte.config.js file, which is no longer supported. The ability to configure SvelteKit via vite.config.js was added in version 2.62.

reference({
			adapter(property) Config.adapter?: Adapter | undefinedYour adapter is run when executing vite build. It determines how the output is converted for different platforms.
undefined
: adapter(alias) adapter(options?: AdapterOptions): Adapter
import adapter()
		})
	]
});

wrangler.toml

wrangler

site.bucket = ".cloudflare/public"
assets.directory = ".cloudflare/public"
assets.binding = "ASSETS" # Exclude this if you don't have a `main` key configured.

wrangler.jsonc

wrangler

{
	"site": {
		"bucket": ".cloudflare/public"
	},
	"assets": {
		"directory": ".cloudflare/public",
		"binding": "ASSETS" // Exclude this if you don't have a `main` key configured.
	}
}

Migrating from Cloudflare Pages

To migrate to Cloudflare Workers:

Remove pages_build_output_dir from your Wrangler configuration and add the main and assets settings.
Remove the adapter’s routes option and any _routes.json files.
Replace wrangler pages dev and wrangler pages deploy with wrangler dev and wrangler deploy. For automatic deployments, use Workers Builds instead of the Pages Git integration.

See Cloudflare’s Workers and Pages compatibility matrix for a comparison of supported features.

Edit this page on GitHub llms.txt

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