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Vercel

To deploy to Vercel, use adapter-vercel.

This adapter will be installed by default when you use adapter-auto, but adding it to your project allows you to specify Vercel-specific options.

Usage

Install with npm i -D @sveltejs/adapter-vercel, then add the adapter to your svelte.config.js:

// @errors: 2307
/// file: svelte.config.js
import adapter from '@sveltejs/adapter-vercel';

export default {
	kit: {
		// default options are shown
		adapter: adapter({
			// if true, will deploy the app using edge functions
			// (https://vercel.com/docs/concepts/functions/edge-functions)
			// rather than serverless functions
			edge: false,

			// an array of dependencies that esbuild should treat
			// as external when bundling functions
			external: [],

			// if true, will split your app into multiple functions
			// instead of creating a single one for the entire app
			split: false
		})
	}
};

Config options

Besides the config options shown above, the Vercel adapter also supports the runtime, regions, maxDuration and memory options for serverless functions and the regions and envVarsInUse options for edge functions. You can set defaults through the adapter options and override them inside +page/layout(.server).js files using the config export.

Environment Variables

Vercel makes a set of deployment-specific environment variables available. Like other environment variables, these are accessible from $env/static/private and $env/dynamic/private (sometimes — more on that later), and inaccessible from their public counterparts. To access one of these variables from the client:

// @errors: 2305
/// file: +layout.server.js
import { VERCEL_COMMIT_REF } from '$env/static/private';

/** @type {import('./$types').LayoutServerLoad} */
export function load() {
	return {
		deploymentGitBranch: VERCEL_COMMIT_REF
	};
}
/// file: +layout.svelte
<script>
	/** @type {import('./$types').LayoutServerData} */
	export let data;
</script>

<p>This staging environment was deployed from {data.deploymentGitBranch}.</p>

Since all of these variables are unchanged between build time and run time when building on Vercel, we recommend using $env/static/private — which will statically replace the variables, enabling optimisations like dead code elimination — rather than $env/dynamic/private. If you're deploying with edge: true you must use $env/static/private, as $env/dynamic/private and $env/dynamic/public are not currently populated in edge functions on Vercel.

Notes

Vercel functions

Vercel functions contained in the /api directory at the project's root will not be included in the deployment — these should be implemented as server endpoints in your SvelteKit app.

Node version

Projects created before a certain date will default to using Node 14, while SvelteKit requires Node 16 or later. You can change the Node version in your project settings.

Troubleshooting

Accessing the file system

You can't access the file system through methods like fs.readFileSync in Serverless/Edge environments. If you need to access files that way, do that during building the app through prerendering. If you have a blog for example and don't want to manage your content through a CMS, then you need to prerender the content (or prerender the endpoint from which you get it) and redeploy your blog everytime you add new content.