Respect "MODE" to set environment variables from another dotenv file similar to Vite

[hammzj]

Describe the bug

Vite uses a process environment variable of MODE to allow a user to declare another .env file like .env.[MODE] and .env.[MODE].local:

https://vite.dev/guide/env-and-mode#env-files

Svelte conflicts with this by only loading .env and .env.local. Instead, Svelte should also load all environment variables from MODE.

Reproduction

• Create a new .env.preview file:

MY_SECRET=1234

• create empty .env and .env.local files

• Run MODE=preview npm run build

If you try to console.log out that secret, it will be undefined, because SvelteKit is not using .env.preview.

Logs

System Info

System:
    OS: macOS 26.6.2
    CPU: (10) arm64 Apple M5
    Memory: 3.02 GB / 32.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.16.0 - /Users/zjh/.volta/tools/image/node/24.16.0/bin/node
    Yarn: 4.18.0 - /Users/zjh/.volta/tools/image/yarn/4.18.0/bin/yarn
    npm: 11.17.0 - /Users/zjh/.volta/tools/image/npm/11.17.0/bin/npm
  Browsers:
    Brave Browser: 151.1.93.136
    Safari: 26.6.2
  npmPackages:
    @sveltejs/adapter-auto: ^6.0.0 => 6.1.1 
    @sveltejs/adapter-vercel: 5 => 5.10.3 
    @sveltejs/kit: ^2.22.0 => 2.70.3 
    @sveltejs/vite-plugin-svelte: ^6.0.0 => 6.2.4 
    svelte: ^5.5.0 => 5.56.10 
    vite: ^7.0.4 => 7.3.6

Severity

annoyance

Additional Information

No response

[teemingc]

Can you check if this is the case with SvelteKit 3? https://next.svelte.dev/docs/kit/migrating-to-sveltekit-3

[TjenWellens]

Yeah, it would be great if sveltekit picked up on vitest mode automatically.

Workaround:
move svelte.config.js into vite.config.ts
works on "@sveltejs/kit": "^2.70.3", // could work on earlier versions, didn't check, I just picked latest

// vite.config.ts
import { defineConfig } from 'vitest/config';
import { loadEnv } from 'vite';
import adapter from '@sveltejs/adapter-cloudflare';

export default defineConfig(({mode}) => {
  const env = loadEnv(mode, process.cwd(), ''); // fyi: not sure what all this does
  const dbMode = env.DB_MODE ?? 'neon';

  return {
		plugins: [sveltekit({ // move entire svelte.config.js into here, but inline the 'kit' property
			preprocess: vitePreprocess(), // could be old way / outdated

			//kit: { // all inside 'kit' is inlined
				alias: {
					'$legacyDatabase':
						dbMode === 'local'
							? 'src/lib/server/db/index.local.ts'
							: 'src/lib/server/db/index.ts',
					'$database':
						dbMode === 'local'
							? 'src/lib/server/db/LocalDatabase.ts'
							: 'src/lib/server/db/NeonDatabase.ts',
				},
				adapter: adapter()
			//} // all inside 'kit' is inlined
		})],

allows me to run npm run dev:runLocal

# package.json
	"scripts": {
		"dev": "vite dev",
		"dev:runLocal": "vite dev --mode runLocal",

which picks up .env.runLocal

#.env.runLocal
DB_MODE="local"

[hammzj]

Can you check if this is the case with SvelteKit 3? https://next.svelte.dev/docs/kit/migrating-to-sveltekit-3

I've been trying to start the upgrade, but it's going slow. I'll need to check in a template project instead.