diff --git a/.changeset/slow-files-stare.md b/.changeset/slow-files-stare.md
new file mode 100644
index 000000000000..e68f7eaee10f
--- /dev/null
+++ b/.changeset/slow-files-stare.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+[fix] allow SvelteKit to be used without bundling
diff --git a/packages/kit/package.json b/packages/kit/package.json
index 12e0eb45144f..f1cf41c77678 100644
--- a/packages/kit/package.json
+++ b/packages/kit/package.json
@@ -14,6 +14,7 @@
 		"@types/cookie": "^0.5.1",
 		"cookie": "^0.5.0",
 		"devalue": "^4.2.0",
+		"esm-env": "^1.0.0",
 		"kleur": "^4.1.5",
 		"magic-string": "^0.27.0",
 		"mime": "^3.0.0",
diff --git a/packages/kit/src/exports/index.js b/packages/kit/src/exports/index.js
index 9efee4666bfa..63326a7fbcbf 100644
--- a/packages/kit/src/exports/index.js
+++ b/packages/kit/src/exports/index.js
@@ -1,4 +1,5 @@
 import { HttpError, Redirect, ActionFailure } from '../runtime/control.js';
+import { BROWSER, DEV } from 'esm-env';
 
 // For some reason we need to type the params as well here,
 // JSdoc doesn't seem to like @type with function overloads
@@ -8,10 +9,7 @@ import { HttpError, Redirect, ActionFailure } from '../runtime/control.js';
  * @param {any} message
  */
 export function error(status, message) {
-	if (
-		(!__SVELTEKIT_BROWSER__ || __SVELTEKIT_DEV__) &&
-		(isNaN(status) || status < 400 || status > 599)
-	) {
+	if ((!BROWSER || DEV) && (isNaN(status) || status < 400 || status > 599)) {
 		throw new Error(`HTTP error status codes must be between 400 and 599 — ${status} is invalid`);
 	}
 
@@ -20,10 +18,7 @@ export function error(status, message) {
 
 /** @type {import('@sveltejs/kit').redirect} */
 export function redirect(status, location) {
-	if (
-		(!__SVELTEKIT_BROWSER__ || __SVELTEKIT_DEV__) &&
-		(isNaN(status) || status < 300 || status > 308)
-	) {
+	if ((!BROWSER || DEV) && (isNaN(status) || status < 300 || status > 308)) {
 		throw new Error('Invalid status code');
 	}
 
diff --git a/packages/kit/src/exports/vite/build/utils.js b/packages/kit/src/exports/vite/build/utils.js
index 00877dc383d3..1d2a49743cd1 100644
--- a/packages/kit/src/exports/vite/build/utils.js
+++ b/packages/kit/src/exports/vite/build/utils.js
@@ -146,8 +146,6 @@ export function get_default_build_config({ config, input, ssr, outDir }) {
 			__SVELTEKIT_ADAPTER_NAME__: JSON.stringify(config.kit.adapter?.name),
 			__SVELTEKIT_APP_VERSION_FILE__: JSON.stringify(`${config.kit.appDir}/version.json`),
 			__SVELTEKIT_APP_VERSION_POLL_INTERVAL__: JSON.stringify(config.kit.version.pollInterval),
-			__SVELTEKIT_BROWSER__: ssr ? 'false' : 'true',
-			__SVELTEKIT_DEV__: 'false',
 			__SVELTEKIT_EMBEDDED__: config.kit.embedded ? 'true' : 'false'
 		},
 		publicDir: ssr ? false : config.kit.files.assets,
diff --git a/packages/kit/src/exports/vite/dev/index.js b/packages/kit/src/exports/vite/dev/index.js
index aba100ef3fa6..56e148509134 100644
--- a/packages/kit/src/exports/vite/dev/index.js
+++ b/packages/kit/src/exports/vite/dev/index.js
@@ -26,12 +26,6 @@ const cwd = process.cwd();
 export async function dev(vite, vite_config, svelte_config) {
 	installPolyfills();
 
-	// @ts-expect-error
-	globalThis.__SVELTEKIT_BROWSER__ = false;
-
-	// @ts-expect-error
-	globalThis.__SVELTEKIT_DEV__ = true;
-
 	sync.init(svelte_config, vite_config.mode);
 
 	/** @type {import('types').Respond} */
diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index 78221d9d30e6..729c51017a2a 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -261,8 +261,6 @@ function kit({ svelte_config }) {
 				},
 				define: {
 					__SVELTEKIT_APP_VERSION_POLL_INTERVAL__: '0',
-					__SVELTEKIT_BROWSER__: config_env.ssrBuild ? 'false' : 'true',
-					__SVELTEKIT_DEV__: 'true',
 					__SVELTEKIT_EMBEDDED__: svelte_config.kit.embedded ? 'true' : 'false'
 				},
 				publicDir: svelte_config.kit.files.assets,
diff --git a/packages/kit/src/runtime/app/environment.js b/packages/kit/src/runtime/app/environment.js
index b8f69708afae..e9a45aed151f 100644
--- a/packages/kit/src/runtime/app/environment.js
+++ b/packages/kit/src/runtime/app/environment.js
@@ -1,11 +1,13 @@
+import { BROWSER, DEV } from 'esm-env';
+
 /**
  * @type {import('$app/environment').browser}
  */
-export const browser = !import.meta.env.SSR;
+export const browser = BROWSER;
 
 /**
  * @type {import('$app/environment').dev}
  */
-export const dev = __SVELTEKIT_DEV__;
+export const dev = DEV;
 
 export { building, version } from '../env.js';
diff --git a/packages/kit/src/runtime/app/forms.js b/packages/kit/src/runtime/app/forms.js
index 841c78c54475..734f91b993da 100644
--- a/packages/kit/src/runtime/app/forms.js
+++ b/packages/kit/src/runtime/app/forms.js
@@ -1,6 +1,7 @@
 import * as devalue from 'devalue';
 import { client } from '../client/singletons.js';
 import { invalidateAll } from './navigation.js';
+import { BROWSER, DEV } from 'esm-env';
 
 /**
  * @param {string} name
@@ -11,10 +12,8 @@ function guard(name) {
 	};
 }
 
-const ssr = import.meta.env.SSR;
-
 /** @type {import('$app/forms').applyAction} */
-export const applyAction = ssr ? guard('applyAction') : client.apply_action;
+export const applyAction = BROWSER ? client.apply_action : guard('applyAction');
 
 /** @type {import('$app/forms').deserialize} */
 export function deserialize(result) {
@@ -27,7 +26,7 @@ export function deserialize(result) {
 
 /** @type {import('$app/forms').enhance} */
 export function enhance(form, submit = () => {}) {
-	if (__SVELTEKIT_DEV__ && form.method !== 'post') {
+	if (DEV && form.method !== 'post') {
 		throw new Error('use:enhance can only be used on <form> fields with method="POST"');
 	}
 
diff --git a/packages/kit/src/runtime/app/navigation.js b/packages/kit/src/runtime/app/navigation.js
index 7104f54d13cd..a7e8b75ecb17 100644
--- a/packages/kit/src/runtime/app/navigation.js
+++ b/packages/kit/src/runtime/app/navigation.js
@@ -1,3 +1,4 @@
+import { BROWSER } from 'esm-env';
 import { client } from '../client/singletons.js';
 
 /**
@@ -9,18 +10,16 @@ function guard(name) {
 	};
 }
 
-const ssr = import.meta.env.SSR;
-
-export const disableScrollHandling = ssr
-	? guard('disableScrollHandling')
-	: client.disable_scroll_handling;
-export const goto = ssr ? guard('goto') : client.goto;
-export const invalidate = ssr ? guard('invalidate') : client.invalidate;
-export const invalidateAll = ssr ? guard('invalidateAll') : client.invalidateAll;
-export const preloadData = ssr ? guard('preloadData') : client.preload_data;
-export const preloadCode = ssr ? guard('preloadCode') : client.preload_code;
-export const beforeNavigate = ssr ? () => {} : client.before_navigate;
-export const afterNavigate = ssr ? () => {} : client.after_navigate;
+export const disableScrollHandling = BROWSER
+	? client.disable_scroll_handling
+	: guard('disableScrollHandling');
+export const goto = BROWSER ? client.goto : guard('goto');
+export const invalidate = BROWSER ? client.invalidate : guard('invalidate');
+export const invalidateAll = BROWSER ? client.invalidateAll : guard('invalidateAll');
+export const preloadData = BROWSER ? client.preload_data : guard('preloadData');
+export const preloadCode = BROWSER ? client.preload_code : guard('preloadCode');
+export const beforeNavigate = BROWSER ? client.before_navigate : () => {};
+export const afterNavigate = BROWSER ? client.after_navigate : () => {};
 
 // TODO remove for 1.0 release
 /** @param {any} _args */
diff --git a/packages/kit/src/runtime/client/client.js b/packages/kit/src/runtime/client/client.js
index e0c096919f01..0bf95223e29b 100644
--- a/packages/kit/src/runtime/client/client.js
+++ b/packages/kit/src/runtime/client/client.js
@@ -1,3 +1,4 @@
+import { DEV } from 'esm-env';
 import { onMount, tick } from 'svelte';
 import {
 	make_trackable,
@@ -383,7 +384,7 @@ export function create_client({ target, base }) {
 
 	/** @param {import('./types').NavigationFinished} result */
 	function initialize(result) {
-		if (__SVELTEKIT_DEV__ && document.querySelector('vite-error-overlay')) return;
+		if (DEV && document.querySelector('vite-error-overlay')) return;
 
 		current = result.state;
 
@@ -560,7 +561,7 @@ export function create_client({ target, base }) {
 
 		const node = await loader();
 
-		if (__SVELTEKIT_DEV__) {
+		if (DEV) {
 			validate_common_exports(node.shared);
 		}
 
@@ -675,7 +676,7 @@ export function create_client({ target, base }) {
 				}
 			});
 
-			if (__SVELTEKIT_DEV__) {
+			if (DEV) {
 				try {
 					lock_fetch();
 					data = (await node.shared.load.call(null, load_input)) ?? null;
@@ -1313,7 +1314,7 @@ export function create_client({ target, base }) {
 		},
 
 		disable_scroll_handling: () => {
-			if (__SVELTEKIT_DEV__ && started && !updating) {
+			if (DEV && started && !updating) {
 				throw new Error('Can only disable scroll handling during navigation');
 			}
 
@@ -1734,7 +1735,7 @@ export function create_client({ target, base }) {
 async function load_data(url, invalid) {
 	const data_url = new URL(url);
 	data_url.pathname = add_data_suffix(url.pathname);
-	if (__SVELTEKIT_DEV__ && url.searchParams.has('x-sveltekit-invalidated')) {
+	if (DEV && url.searchParams.has('x-sveltekit-invalidated')) {
 		throw new Error('Cannot used reserved query parameter "x-sveltekit-invalidated"');
 	}
 	data_url.searchParams.append(
@@ -1827,7 +1828,7 @@ function add_url_properties(type, target) {
 }
 
 function pre_update() {
-	if (__SVELTEKIT_DEV__) {
+	if (DEV) {
 		return () => {
 			check_for_removed_attributes();
 		};
@@ -1866,7 +1867,7 @@ function reset_focus() {
 	}
 }
 
-if (__SVELTEKIT_DEV__) {
+if (DEV) {
 	// Nasty hack to silence harmless warnings the user can do nothing about
 	const console_warn = console.warn;
 	console.warn = function warn(...args) {
diff --git a/packages/kit/src/runtime/client/fetcher.js b/packages/kit/src/runtime/client/fetcher.js
index fb89843f8505..36666ef29c41 100644
--- a/packages/kit/src/runtime/client/fetcher.js
+++ b/packages/kit/src/runtime/client/fetcher.js
@@ -1,3 +1,4 @@
+import { DEV } from 'esm-env';
 import { hash } from '../hash.js';
 
 let loading = 0;
@@ -12,7 +13,7 @@ export function unlock_fetch() {
 	loading -= 1;
 }
 
-if (import.meta.env.DEV) {
+if (DEV) {
 	let can_inspect_stack_trace = false;
 
 	const check_stack_trace = async () => {
diff --git a/packages/kit/src/runtime/client/start.js b/packages/kit/src/runtime/client/start.js
index 7b113f53fbf8..16ad70ed0e90 100644
--- a/packages/kit/src/runtime/client/start.js
+++ b/packages/kit/src/runtime/client/start.js
@@ -1,3 +1,4 @@
+import { DEV } from 'esm-env';
 import { create_client } from './client.js';
 import { init } from './singletons.js';
 import { set_paths } from '../paths.js';
@@ -21,7 +22,7 @@ export async function start({ env, hydrate, paths, target, version }) {
 	set_paths(paths);
 	set_version(version);
 
-	if (__SVELTEKIT_DEV__ && target === document.body) {
+	if (DEV && target === document.body) {
 		console.warn(
 			`Placing %sveltekit.body% directly inside <body> is not recommended, as your app may break for users who have certain browser extensions installed.\n\nConsider wrapping it in an element:\n\n<div style="display: contents">\n  %sveltekit.body%\n</div>`
 		);
diff --git a/packages/kit/src/runtime/client/utils.js b/packages/kit/src/runtime/client/utils.js
index 7f953d1f4dbd..8e1a047648d4 100644
--- a/packages/kit/src/runtime/client/utils.js
+++ b/packages/kit/src/runtime/client/utils.js
@@ -1,3 +1,4 @@
+import { BROWSER, DEV } from 'esm-env';
 import { writable } from 'svelte/store';
 import { assets } from '../paths.js';
 import { version } from '../env.js';
@@ -50,7 +51,9 @@ function link_option(element, name) {
 		element.getAttribute(`data-sveltekit-${name}`)
 	);
 
-	if (__SVELTEKIT_DEV__) validate_link_option(element, name, value);
+	if (DEV) {
+		validate_link_option(element, name, value);
+	}
 
 	return value;
 }
@@ -209,7 +212,7 @@ export function create_updated_store() {
 	let timeout;
 
 	async function check() {
-		if (import.meta.env.DEV || import.meta.env.SSR) return false;
+		if (DEV || !BROWSER) return false;
 
 		clearTimeout(timeout);
 
diff --git a/packages/kit/src/runtime/server/index.js b/packages/kit/src/runtime/server/index.js
index dfce7d8f2703..1217079c62a5 100644
--- a/packages/kit/src/runtime/server/index.js
+++ b/packages/kit/src/runtime/server/index.js
@@ -1,3 +1,4 @@
+import { DEV } from 'esm-env';
 import { is_endpoint_request, render_endpoint } from './endpoint.js';
 import { render_page } from './page/index.js';
 import { render_response } from './page/render.js';
@@ -202,7 +203,7 @@ export async function respond(request, options, state) {
 					options.manifest._.nodes[route.page.leaf]()
 				]);
 
-				if (__SVELTEKIT_DEV__) {
+				if (DEV) {
 					const layouts = nodes.slice(0, -1);
 					const page = nodes.at(-1);
 
@@ -224,7 +225,7 @@ export async function respond(request, options, state) {
 				const node = await route.endpoint();
 				trailing_slash = node.trailingSlash;
 
-				if (__SVELTEKIT_DEV__) {
+				if (DEV) {
 					validate_server_exports(node, /** @type {string} */ (route.endpoint_id));
 				}
 			}
diff --git a/packages/kit/src/utils/url.js b/packages/kit/src/utils/url.js
index db4e6d882137..d0c917b2bb64 100644
--- a/packages/kit/src/utils/url.js
+++ b/packages/kit/src/utils/url.js
@@ -1,3 +1,5 @@
+import { BROWSER } from 'esm-env';
+
 const absolute = /^([a-z]+:)?\/?\//;
 const scheme = /^[a-z]+:/;
 
@@ -101,7 +103,7 @@ export function make_trackable(url, callback) {
 		});
 	}
 
-	if (!__SVELTEKIT_BROWSER__) {
+	if (!BROWSER) {
 		// @ts-ignore
 		tracked[Symbol.for('nodejs.util.inspect.custom')] = (depth, opts, inspect) => {
 			return inspect(url, opts);
diff --git a/packages/kit/src/utils/url.spec.js b/packages/kit/src/utils/url.spec.js
index f405039f7fdd..383c30ea2e12 100644
--- a/packages/kit/src/utils/url.spec.js
+++ b/packages/kit/src/utils/url.spec.js
@@ -2,9 +2,6 @@ import * as assert from 'uvu/assert';
 import { describe } from './unit_test.js';
 import { resolve, normalize_path, make_trackable, disable_search } from './url.js';
 
-// @ts-expect-error define global required in url.js
-globalThis.__SVELTEKIT_BROWSER__ = false;
-
 describe('resolve', (test) => {
 	test('resolves a root-relative path', () => {
 		assert.equal(resolve('/a/b/c', '/x/y/z'), '/x/y/z');
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index ee84774810dd..5a2b9aa66df8 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -274,6 +274,7 @@ importers:
       '@types/set-cookie-parser': ^2.4.2
       cookie: ^0.5.0
       devalue: ^4.2.0
+      esm-env: ^1.0.0
       kleur: ^4.1.5
       magic-string: ^0.27.0
       marked: ^4.2.3
@@ -294,6 +295,7 @@ importers:
       '@types/cookie': 0.5.1
       cookie: 0.5.0
       devalue: 4.2.0
+      esm-env: 1.0.0
       kleur: 4.1.5
       magic-string: 0.27.0
       mime: 3.0.0
@@ -2275,6 +2277,10 @@ packages:
     engines: {node: '>=0.8.0'}
     dev: true
 
+  /esm-env/1.0.0:
+    resolution: {integrity: sha512-Cf6VksWPsTuW01vU9Mk/3vRue91Zevka5SjyNf3nEpokFRuqt/KjUQoGAwq9qMmhpLTHmXzSIrFRw8zxWzmFBA==}
+    dev: false
+
   /esprima/4.0.1:
     resolution: {integrity: sha512-eGuFFw7Upda+g4p+QHvnW0RyTX/SVeJBDM/gCtMARO0cLuT2HcEKnTPvhjV6aGeqrCB/sbNop0Kszm0jsaWU4A==}
     engines: {node: '>=4'}