diff --git a/.changeset/cool-spoons-tap.md b/.changeset/cool-spoons-tap.md
new file mode 100644
index 000000000000..461db03a81da
--- /dev/null
+++ b/.changeset/cool-spoons-tap.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: warn on undeclared shorthand event handlers on `<svelte:window>`, `<svelte:document>` and `<svelte:body>`
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteBody.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteBody.js
index 82bc592c1409..1571961badda 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteBody.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteBody.js
@@ -2,7 +2,7 @@
 /** @import { Context } from '../types' */
 import * as e from '../../../errors.js';
 import { is_event_attribute } from '../../../utils/ast.js';
-import { disallow_children } from './shared/special-element.js';
+import { check_global_event_reference, disallow_children } from './shared/special-element.js';
 
 /**
  * @param {AST.SvelteBody} node
@@ -11,10 +11,9 @@ import { disallow_children } from './shared/special-element.js';
 export function SvelteBody(node, context) {
 	disallow_children(node);
 	for (const attribute of node.attributes) {
-		if (
-			attribute.type === 'SpreadAttribute' ||
-			(attribute.type === 'Attribute' && !is_event_attribute(attribute))
-		) {
+		if (attribute.type === 'Attribute' && is_event_attribute(attribute)) {
+			check_global_event_reference(attribute, context);
+		} else if (attribute.type === 'SpreadAttribute' || attribute.type === 'Attribute') {
 			e.svelte_body_illegal_attribute(attribute);
 		}
 	}
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteDocument.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteDocument.js
index fe54ebf30d42..4c092defb0a6 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteDocument.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteDocument.js
@@ -1,6 +1,6 @@
 /** @import { AST } from '#compiler' */
 /** @import { Context } from '../types' */
-import { disallow_children } from './shared/special-element.js';
+import { check_global_event_reference, disallow_children } from './shared/special-element.js';
 import * as e from '../../../errors.js';
 import { is_event_attribute } from '../../../utils/ast.js';
 
@@ -12,10 +12,9 @@ export function SvelteDocument(node, context) {
 	disallow_children(node);
 
 	for (const attribute of node.attributes) {
-		if (
-			attribute.type === 'SpreadAttribute' ||
-			(attribute.type === 'Attribute' && !is_event_attribute(attribute))
-		) {
+		if (attribute.type === 'Attribute' && is_event_attribute(attribute)) {
+			check_global_event_reference(attribute, context);
+		} else if (attribute.type === 'SpreadAttribute' || attribute.type === 'Attribute') {
 			e.illegal_element_attribute(attribute, 'svelte:document');
 		}
 	}
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteWindow.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteWindow.js
index 20f5abc5d6b8..44c448fadd68 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteWindow.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteWindow.js
@@ -1,6 +1,6 @@
 /** @import { AST } from '#compiler' */
 /** @import { Context } from '../types' */
-import { disallow_children } from './shared/special-element.js';
+import { check_global_event_reference, disallow_children } from './shared/special-element.js';
 import * as e from '../../../errors.js';
 import { is_event_attribute } from '../../../utils/ast.js';
 
@@ -12,10 +12,9 @@ export function SvelteWindow(node, context) {
 	disallow_children(node);
 
 	for (const attribute of node.attributes) {
-		if (
-			attribute.type === 'SpreadAttribute' ||
-			(attribute.type === 'Attribute' && !is_event_attribute(attribute))
-		) {
+		if (attribute.type === 'Attribute' && is_event_attribute(attribute)) {
+			check_global_event_reference(attribute, context);
+		} else if (attribute.type === 'SpreadAttribute' || attribute.type === 'Attribute') {
 			e.illegal_element_attribute(attribute, 'svelte:window');
 		}
 	}
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/special-element.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/special-element.js
index e72b3c6b2a1f..4fe8090f7228 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/special-element.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/special-element.js
@@ -1,5 +1,28 @@
 /** @import { AST } from '#compiler' */
+/** @import { Context } from '../../types' */
+import { get_attribute_expression } from '../../../../utils/ast.js';
 import * as e from '../../../../errors.js';
+import * as w from '../../../../warnings.js';
+
+/**
+ * Warns when an event attribute uses the shorthand form (`{onclick}`) but the
+ * referenced name isn't declared, so it silently resolves to the global handler.
+ * @param {AST.Attribute} attribute
+ * @param {Context} context
+ */
+export function check_global_event_reference(attribute, context) {
+	const value = get_attribute_expression(
+		/** @type {AST.Attribute & { value: [AST.ExpressionTag] | AST.ExpressionTag }} */ (attribute)
+	);
+
+	if (
+		value.type === 'Identifier' &&
+		value.name === attribute.name &&
+		!context.state.scope.get(value.name)
+	) {
+		w.attribute_global_event_reference(attribute, attribute.name);
+	}
+}
 
 /**
  * @param {AST.SvelteBody | AST.SvelteDocument | AST.SvelteOptionsRaw | AST.SvelteWindow} node
diff --git a/packages/svelte/tests/validator/samples/global-event-reference-special-elements/_config.js b/packages/svelte/tests/validator/samples/global-event-reference-special-elements/_config.js
new file mode 100644
index 000000000000..f47bee71df87
--- /dev/null
+++ b/packages/svelte/tests/validator/samples/global-event-reference-special-elements/_config.js
@@ -0,0 +1,3 @@
+import { test } from '../../test';
+
+export default test({});
diff --git a/packages/svelte/tests/validator/samples/global-event-reference-special-elements/input.svelte b/packages/svelte/tests/validator/samples/global-event-reference-special-elements/input.svelte
new file mode 100644
index 000000000000..3ea7674419a1
--- /dev/null
+++ b/packages/svelte/tests/validator/samples/global-event-reference-special-elements/input.svelte
@@ -0,0 +1,7 @@
+<script>
+	let onkeydown;
+</script>
+
+<svelte:window {onkeydown} {onresize} />
+<svelte:document {onvisibilitychange} />
+<svelte:body {onfocus} />
diff --git a/packages/svelte/tests/validator/samples/global-event-reference-special-elements/warnings.json b/packages/svelte/tests/validator/samples/global-event-reference-special-elements/warnings.json
new file mode 100644
index 000000000000..e69a45ab3eeb
--- /dev/null
+++ b/packages/svelte/tests/validator/samples/global-event-reference-special-elements/warnings.json
@@ -0,0 +1,38 @@
+[
+	{
+		"code": "attribute_global_event_reference",
+		"message": "You are referencing `globalThis.onresize`. Did you forget to declare a variable with that name?",
+		"start": {
+			"column": 27,
+			"line": 5
+		},
+		"end": {
+			"column": 37,
+			"line": 5
+		}
+	},
+	{
+		"code": "attribute_global_event_reference",
+		"message": "You are referencing `globalThis.onvisibilitychange`. Did you forget to declare a variable with that name?",
+		"start": {
+			"column": 17,
+			"line": 6
+		},
+		"end": {
+			"column": 37,
+			"line": 6
+		}
+	},
+	{
+		"code": "attribute_global_event_reference",
+		"message": "You are referencing `globalThis.onfocus`. Did you forget to declare a variable with that name?",
+		"start": {
+			"column": 13,
+			"line": 7
+		},
+		"end": {
+			"column": 22,
+			"line": 7
+		}
+	}
+]