diff --git a/packages/kit/src/core/config/index.spec.js b/packages/kit/src/core/config/index.spec.js
index 90da427483d7..ed0c5c47732a 100644
--- a/packages/kit/src/core/config/index.spec.js
+++ b/packages/kit/src/core/config/index.spec.js
@@ -97,6 +97,9 @@ const get_defaults = (prefix = '') => ({
 		moduleExtensions: ['.js', '.ts'],
 		output: { preloadStrategy: 'modulepreload', bundleStrategy: 'split' },
 		outDir: join(prefix, '.svelte-kit'),
+		remoteFunctions: {
+			allowedPaths: []
+		},
 		router: {
 			type: 'pathname',
 			resolution: 'client'
diff --git a/packages/kit/src/core/config/options.js b/packages/kit/src/core/config/options.js
index 577ca4c9445d..948032370c41 100644
--- a/packages/kit/src/core/config/options.js
+++ b/packages/kit/src/core/config/options.js
@@ -264,6 +264,10 @@ const options = object(
 				})
 			}),
 
+			remoteFunctions: object({
+				allowedPaths: string_array([])
+			}),
+
 			router: object({
 				type: list(['pathname', 'hash']),
 				resolution: list(['client', 'server'])
diff --git a/packages/kit/src/core/sync/create_manifest_data/index.js b/packages/kit/src/core/sync/create_manifest_data/index.js
index a121ac189be0..91f48f672dfd 100644
--- a/packages/kit/src/core/sync/create_manifest_data/index.js
+++ b/packages/kit/src/core/sync/create_manifest_data/index.js
@@ -480,8 +480,10 @@ function create_remotes(config, cwd) {
 	/** @type {import('types').ManifestData['remotes']} */
 	const remotes = [];
 
+	const externals = config.kit.remoteFunctions.allowedPaths.map((dir) => path.resolve(dir));
+
 	// TODO could files live in other directories, including node_modules?
-	for (const dir of [config.kit.files.lib, config.kit.files.routes]) {
+	for (const dir of [config.kit.files.lib, config.kit.files.routes, ...externals]) {
 		if (!fs.existsSync(dir)) continue;
 
 		for (const file of walk(dir)) {
diff --git a/packages/kit/src/exports/public.d.ts b/packages/kit/src/exports/public.d.ts
index df3996a5bf69..82fcf2ea056f 100644
--- a/packages/kit/src/exports/public.d.ts
+++ b/packages/kit/src/exports/public.d.ts
@@ -657,6 +657,15 @@ export interface KitConfig {
 		 */
 		origin?: string;
 	};
+	remoteFunctions?: {
+		/**
+		 * A list of external paths that are allowed to provide remote functions.
+		 * By default, remote functions are only allowed inside the `routes` and `lib` folders.
+		 *
+		 * Accepts absolute paths or paths relative to the project root.
+		 */
+		allowedPaths?: string[];
+	};
 	router?: {
 		/**
 		 * What type of client-side router to use.
diff --git a/packages/kit/src/exports/vite/dev/index.js b/packages/kit/src/exports/vite/dev/index.js
index a5f211efa9af..1366f68b77eb 100644
--- a/packages/kit/src/exports/vite/dev/index.js
+++ b/packages/kit/src/exports/vite/dev/index.js
@@ -29,9 +29,10 @@ const vite_css_query_regex = /(?:\?|&)(?:raw|url|inline)(?:&|$)/;
  * @param {import('vite').ViteDevServer} vite
  * @param {import('vite').ResolvedConfig} vite_config
  * @param {import('types').ValidatedConfig} svelte_config
+ * @param {(manifest_data: import('types').ManifestData) => void} manifest_cb
  * @return {Promise<Promise<() => void>>}
  */
-export async function dev(vite, vite_config, svelte_config) {
+export async function dev(vite, vite_config, svelte_config, manifest_cb) {
 	installPolyfills();
 
 	const async_local_storage = new AsyncLocalStorage();
@@ -108,7 +109,7 @@ export async function dev(vite, vite_config, svelte_config) {
 	function update_manifest() {
 		try {
 			({ manifest_data } = sync.create(svelte_config));
-
+			manifest_cb(manifest_data);
 			if (manifest_error) {
 				manifest_error = null;
 				vite.ws.send({ type: 'full-reload' });
diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index 7486574c674d..c608a455c143 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -35,7 +35,7 @@ import {
 	sveltekit_server
 } from './module_ids.js';
 import { import_peer } from '../../utils/import.js';
-import { compact } from '../../utils/array.js';
+import { compact, conjoin } from '../../utils/array.js';
 import { build_remotes, treeshake_prerendered_remotes } from './build/build_remote.js';
 
 const cwd = process.cwd();
@@ -661,6 +661,24 @@ Tips:
 				}
 			}
 
+			if (!manifest_data.remotes.some((remote) => remote.hash === hashed)) {
+				const relative_path = path.relative(dev_server.config.root, id);
+				const fn_names = [...remotes.values()].flat().map((name) => `"${name}"`);
+				const has_multiple = fn_names.length !== 1;
+				console.warn(
+					colors
+						.bold()
+						.yellow(
+							`Remote function${has_multiple ? 's' : ''} ${conjoin(fn_names)} from ${relative_path} ${has_multiple ? 'are' : 'is'} not accessible by default.`
+						)
+				);
+				console.warn(
+					colors.yellow(
+						`To whitelist ${has_multiple ? 'them' : 'it'}, add "${path.dirname(relative_path)}" to \`kit.remoteFunctions.allowedPaths\` in \`svelte.config.js\`.`
+					)
+				);
+			}
+
 			let namespace = '__remote';
 			let uid = 1;
 			while (remotes.has(namespace)) namespace = `__remote${uid++}`;
@@ -835,7 +853,9 @@ Tips:
 		 * @see https://vitejs.dev/guide/api-plugin.html#configureserver
 		 */
 		async configureServer(vite) {
-			return await dev(vite, vite_config, svelte_config);
+			return await dev(vite, vite_config, svelte_config, (_manifest_data) => {
+				manifest_data = _manifest_data;
+			});
 		},
 
 		/**
diff --git a/packages/kit/src/runtime/server/cookie.js b/packages/kit/src/runtime/server/cookie.js
index 2e683543a534..9019c86f0517 100644
--- a/packages/kit/src/runtime/server/cookie.js
+++ b/packages/kit/src/runtime/server/cookie.js
@@ -1,4 +1,5 @@
 import { parse, serialize } from 'cookie';
+import { conjoin } from '../../utils/array.js';
 import { normalize_path, resolve } from '../../utils/url.js';
 import { add_data_suffix } from '../pathname.js';
 
@@ -286,11 +287,3 @@ export function add_cookies_to_headers(headers, cookies) {
 		}
 	}
 }
-
-/**
- * @param {string[]} array
- */
-function conjoin(array) {
-	if (array.length <= 2) return array.join(' and ');
-	return `${array.slice(0, -1).join(', ')} and ${array.at(-1)}`;
-}
diff --git a/packages/kit/src/utils/array.js b/packages/kit/src/utils/array.js
index 08f93845149b..1d6dc4b6abce 100644
--- a/packages/kit/src/utils/array.js
+++ b/packages/kit/src/utils/array.js
@@ -7,3 +7,12 @@
 export function compact(arr) {
 	return arr.filter(/** @returns {val is NonNullable<T>} */ (val) => val != null);
 }
+
+/**
+ * Joins an array of strings with commas and 'and'.
+ * @param {string[]} array
+ */
+export function conjoin(array) {
+	if (array.length <= 2) return array.join(' and ');
+	return `${array.slice(0, -1).join(', ')} and ${array.at(-1)}`;
+}
diff --git a/packages/kit/test/apps/basics/src/external-not-accessible/external.remote.js b/packages/kit/test/apps/basics/src/external-not-accessible/external.remote.js
new file mode 100644
index 000000000000..5c883ceee850
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/external-not-accessible/external.remote.js
@@ -0,0 +1,3 @@
+import { query } from '$app/server';
+
+export const external_not_accessible = query(async () => 'external failure');
diff --git a/packages/kit/test/apps/basics/src/external-remotes/external.remote.js b/packages/kit/test/apps/basics/src/external-remotes/external.remote.js
new file mode 100644
index 000000000000..ea5b438b138c
--- /dev/null
+++ b/packages/kit/test/apps/basics/src/external-remotes/external.remote.js
@@ -0,0 +1,3 @@
+import { query } from '$app/server';
+
+export const external = query(async () => 'external success');
diff --git a/packages/kit/test/apps/basics/src/routes/remote/+page.svelte b/packages/kit/test/apps/basics/src/routes/remote/+page.svelte
index a05f83efb528..fa54e28903cd 100644
--- a/packages/kit/test/apps/basics/src/routes/remote/+page.svelte
+++ b/packages/kit/test/apps/basics/src/routes/remote/+page.svelte
@@ -1,6 +1,8 @@
 <script>
 	import { browser } from '$app/environment';
 	import { refreshAll } from '$app/navigation';
+	import { external } from '../../external-remotes/external.remote.js';
+	import { external_not_accessible } from '../../external-not-accessible/external.remote.js';
 	import { add, get_count, set_count, set_count_server } from './query-command.remote.js';
 
 	let { data } = $props();
@@ -9,6 +11,8 @@
 	let release;
 
 	const count = browser ? get_count() : null; // so that we get a remote request in the browser
+	const external_result = browser ? external() : null;
+	const external_failure = browser ? external_not_accessible() : null;
 </script>
 
 <p id="echo-result">{data.echo_result}</p>
@@ -65,3 +69,15 @@
 <button id="refresh-remote-only" onclick={() => refreshAll({ includeLoadFunctions: false })}>
 	refreshAll (remote functions only)
 </button>
+
+<p id="external-success">
+	{#await external_result then result}{result}{/await}
+</p>
+
+<p id="external-failure">
+	{#await external_failure then result}
+		{result}
+	{:catch error}
+		{error}
+	{/await}
+</p>
diff --git a/packages/kit/test/apps/basics/svelte.config.js b/packages/kit/test/apps/basics/svelte.config.js
index 2410ff83d57f..ac4aeaf51b7c 100644
--- a/packages/kit/test/apps/basics/svelte.config.js
+++ b/packages/kit/test/apps/basics/svelte.config.js
@@ -41,8 +41,13 @@ const config = {
 		version: {
 			name: 'TEST_VERSION'
 		},
+
 		router: {
 			resolution: /** @type {'client' | 'server'} */ (process.env.ROUTER_RESOLUTION) || 'client'
+		},
+
+		remoteFunctions: {
+			allowedPaths: ['src/external-remotes']
 		}
 	}
 };
diff --git a/packages/kit/test/apps/basics/test/client.test.js b/packages/kit/test/apps/basics/test/client.test.js
index c1fc7d0fb5b6..c6a2c0154c73 100644
--- a/packages/kit/test/apps/basics/test/client.test.js
+++ b/packages/kit/test/apps/basics/test/client.test.js
@@ -1834,4 +1834,11 @@ test.describe('remote functions', () => {
 		await page.click('button:nth-of-type(4)');
 		await expect(page.locator('p')).toHaveText('success');
 	});
+
+	test('external remotes work', async ({ page }) => {
+		await page.goto('/remote');
+		await expect(page.locator('#external-success')).toHaveText('external success');
+		await expect(page.locator('#external-failure')).not.toHaveText('external failure');
+		await expect(page.locator('#external-failure')).toHaveText('Failed to execute remote function');
+	});
 });
diff --git a/packages/kit/types/index.d.ts b/packages/kit/types/index.d.ts
index 7781c0ab58fa..4a188b3a5c77 100644
--- a/packages/kit/types/index.d.ts
+++ b/packages/kit/types/index.d.ts
@@ -634,6 +634,15 @@ declare module '@sveltejs/kit' {
 			 */
 			origin?: string;
 		};
+		remoteFunctions?: {
+			/**
+			 * A list of external paths that are allowed to provide remote functions.
+			 * By default, remote functions are only allowed inside the `routes` and `lib` folders.
+			 *
+			 * Accepts absolute paths or paths relative to the project root.
+			 */
+			allowedPaths?: string[];
+		};
 		router?: {
 			/**
 			 * What type of client-side router to use.