diff --git a/.changeset/sour-wings-taste.md b/.changeset/sour-wings-taste.md
new file mode 100644
index 000000000..1d71ba9f7
--- /dev/null
+++ b/.changeset/sour-wings-taste.md
@@ -0,0 +1,5 @@
+---
+'sv': patch
+---
+
+fix(cli): `vite.config.*` file detection works for both .js and .ts variants
diff --git a/packages/addons/devtools-json/index.ts b/packages/addons/devtools-json/index.ts
index 4198ba47c..625497d6b 100644
--- a/packages/addons/devtools-json/index.ts
+++ b/packages/addons/devtools-json/index.ts
@@ -8,13 +8,11 @@ export default defineAddon({
 	homepage: 'https://github.com/ChromeDevTools/vite-plugin-devtools-json',
 	options: {},
 
-	run: ({ sv, typescript }) => {
-		const ext = typescript ? 'ts' : 'js';
-
+	run: ({ sv, viteConfigFile }) => {
 		sv.devDependency('vite-plugin-devtools-json', '^1.0.0');
 
 		// add the vite plugin
-		sv.file(`vite.config.${ext}`, (content) => {
+		sv.file(viteConfigFile, (content) => {
 			const { ast, generateCode } = parseScript(content);
 
 			const vitePluginName = 'devtoolsJson';
diff --git a/packages/addons/paraglide/index.ts b/packages/addons/paraglide/index.ts
index c432244d9..0809a0a36 100644
--- a/packages/addons/paraglide/index.ts
+++ b/packages/addons/paraglide/index.ts
@@ -55,7 +55,7 @@ export default defineAddon({
 	setup: ({ kit, unsupported }) => {
 		if (!kit) unsupported('Requires SvelteKit');
 	},
-	run: ({ sv, options, typescript, kit }) => {
+	run: ({ sv, options, viteConfigFile, typescript, kit }) => {
 		const ext = typescript ? 'ts' : 'js';
 		if (!kit) throw new Error('SvelteKit is required');
 
@@ -81,7 +81,7 @@ export default defineAddon({
 		});
 
 		// add the vite plugin
-		sv.file(`vite.config.${ext}`, (content) => {
+		sv.file(viteConfigFile, (content) => {
 			const { ast, generateCode } = parseScript(content);
 
 			const vitePluginName = 'paraglideVitePlugin';
diff --git a/packages/addons/tailwindcss/index.ts b/packages/addons/tailwindcss/index.ts
index 78dee7358..614a15b65 100644
--- a/packages/addons/tailwindcss/index.ts
+++ b/packages/addons/tailwindcss/index.ts
@@ -41,8 +41,7 @@ export default defineAddon({
 	shortDescription: 'css framework',
 	homepage: 'https://tailwindcss.com',
 	options,
-	run: ({ sv, options, typescript, kit, dependencyVersion }) => {
-		const ext = typescript ? 'ts' : 'js';
+	run: ({ sv, options, viteConfigFile, typescript, kit, dependencyVersion }) => {
 		const prettierInstalled = Boolean(dependencyVersion('prettier'));
 
 		sv.devDependency('tailwindcss', '^4.0.0');
@@ -57,7 +56,7 @@ export default defineAddon({
 		}
 
 		// add the vite plugin
-		sv.file(`vite.config.${ext}`, (content) => {
+		sv.file(viteConfigFile, (content) => {
 			const { ast, generateCode } = parseScript(content);
 
 			const vitePluginName = 'tailwindcss';
diff --git a/packages/addons/vitest-addon/index.ts b/packages/addons/vitest-addon/index.ts
index 57e6c0763..895d4e051 100644
--- a/packages/addons/vitest-addon/index.ts
+++ b/packages/addons/vitest-addon/index.ts
@@ -20,7 +20,7 @@ export default defineAddon({
 	shortDescription: 'unit testing',
 	homepage: 'https://vitest.dev',
 	options,
-	run: ({ sv, typescript, kit, options }) => {
+	run: ({ sv, viteConfigFile, typescript, kit, options }) => {
 		const ext = typescript ? 'ts' : 'js';
 		const unitTesting = options.usages.includes('unit');
 		const componentTesting = options.usages.includes('component');
@@ -96,11 +96,11 @@ export default defineAddon({
 				`;
 			});
 		}
-		sv.file(`vite.config.${ext}`, (content) => {
+		sv.file(viteConfigFile, (content) => {
 			const { ast, generateCode } = parseScript(content);
 
 			const clientObjectExpression = object.create({
-				extends: `./vite.config.${ext}`,
+				extends: `./${viteConfigFile}`,
 				test: {
 					name: 'client',
 					environment: 'browser',
@@ -116,7 +116,7 @@ export default defineAddon({
 			});
 
 			const serverObjectExpression = object.create({
-				extends: `./vite.config.${ext}`,
+				extends: `./${viteConfigFile}`,
 				test: {
 					name: 'server',
 					environment: 'node',
diff --git a/packages/cli/commands/add/utils.ts b/packages/cli/commands/add/utils.ts
index 2c2900c53..b76a8f015 100644
--- a/packages/cli/commands/add/utils.ts
+++ b/packages/cli/commands/add/utils.ts
@@ -111,6 +111,7 @@ export const commonFilePaths = {
 	packageJson: 'package.json',
 	svelteConfig: 'svelte.config.js',
 	tsconfig: 'tsconfig.json',
+	viteConfig: 'vite.config.js',
 	viteConfigTS: 'vite.config.ts'
 } as const;
 
diff --git a/packages/cli/commands/add/workspace.ts b/packages/cli/commands/add/workspace.ts
index 480db5b9f..468e86d20 100644
--- a/packages/cli/commands/add/workspace.ts
+++ b/packages/cli/commands/add/workspace.ts
@@ -23,6 +23,8 @@ export async function createWorkspace({
 	const viteConfigPath = path.join(resolvedCwd, commonFilePaths.viteConfigTS);
 	let usesTypescript = fs.existsSync(viteConfigPath);
 
+	const viteConfigFile = usesTypescript ? commonFilePaths.viteConfigTS : commonFilePaths.viteConfig;
+
 	if (TESTING) {
 		// while executing tests, we only look into the direct `cwd`
 		// as we might detect the monorepo `tsconfig.json` otherwise.
@@ -55,6 +57,7 @@ export async function createWorkspace({
 		options,
 		packageManager: packageManager ?? (await detect({ cwd }))?.name ?? getUserAgent() ?? 'npm',
 		typescript: usesTypescript,
+		viteConfigFile,
 		kit: dependencies['@sveltejs/kit'] ? parseKitOptions(resolvedCwd) : undefined,
 		dependencyVersion: (pkg) => dependencies[pkg]
 	};
diff --git a/packages/core/addon/workspace.ts b/packages/core/addon/workspace.ts
index a6525d44b..4fa43ffb0 100644
--- a/packages/core/addon/workspace.ts
+++ b/packages/core/addon/workspace.ts
@@ -13,6 +13,7 @@ export type Workspace<Args extends OptionDefinition> = {
 	 */
 	dependencyVersion: (pkg: string) => string | undefined;
 	typescript: boolean;
+	viteConfigFile: string;
 	kit: { libDirectory: string; routesDirectory: string } | undefined;
 	packageManager: PackageManager;
 };