diff --git a/src/wp-admin/async-upload.php b/src/wp-admin/async-upload.php
index 40b50e1e9907f..5fbdd370c5c1a 100644
--- a/src/wp-admin/async-upload.php
+++ b/src/wp-admin/async-upload.php
@@ -145,7 +145,7 @@
 		$_FILES['async-upload']['name']
 	);
 
-	echo '<script>_.delay(function() {wp.a11y.speak(' . wp_json_encode( $speak_message ) . ");}, 1500);jQuery( 'button#{$button_unique_id}' ).on( 'click', function() {jQuery(this).parents('div.media-item').slideUp(200, function(){jQuery(this).remove();wp.a11y.speak( wp.i18n.__( 'Error dismissed.' ) );jQuery( '#plupload-browse-button' ).trigger( 'focus' );})});</script>\n";
+	echo '<script>_.delay(function() {wp.a11y.speak(' . wp_json_encode( $speak_message, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) . ");}, 1500);jQuery( 'button#{$button_unique_id}' ).on( 'click', function() {jQuery(this).parents('div.media-item').slideUp(200, function(){jQuery(this).remove();wp.a11y.speak( wp.i18n.__( 'Error dismissed.' ) );jQuery( '#plupload-browse-button' ).trigger( 'focus' );})});</script>\n";
 	exit;
 }
 
diff --git a/src/wp-admin/customize.php b/src/wp-admin/customize.php
index fbac0dd2420b5..07f74427d57f8 100644
--- a/src/wp-admin/customize.php
+++ b/src/wp-admin/customize.php
@@ -62,7 +62,7 @@
 		?>
 		<?php wp_print_scripts( array( 'wp-util' ) ); ?>
 		<script>
-			wp.ajax.post( 'customize_save', <?php echo wp_json_encode( $request_args ); ?> );
+			wp.ajax.post( 'customize_save', <?php echo wp_json_encode( $request_args, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ); ?> );
 		</script>
 		<?php
 		$script = ob_get_clean();
@@ -158,7 +158,7 @@
 <title><?php echo esc_html( $admin_title ); ?></title>
 
 <script type="text/javascript">
-var ajaxurl = <?php echo wp_json_encode( admin_url( 'admin-ajax.php', 'relative' ) ); ?>,
+var ajaxurl = <?php echo wp_json_encode( admin_url( 'admin-ajax.php', 'relative' ), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ); ?>,
 	pagenow = 'customize';
 </script>
 
diff --git a/src/wp-admin/edit-form-blocks.php b/src/wp-admin/edit-form-blocks.php
index 837a6c6fe20f2..98f5c223f4017 100644
--- a/src/wp-admin/edit-form-blocks.php
+++ b/src/wp-admin/edit-form-blocks.php
@@ -115,7 +115,7 @@ static function ( $classes ) {
 
 wp_add_inline_script(
 	'wp-blocks',
-	sprintf( 'wp.blocks.setCategories( %s );', wp_json_encode( get_block_categories( $post ) ) ),
+	sprintf( 'wp.blocks.setCategories( %s );', wp_json_encode( get_block_categories( $post ), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ),
 	'after'
 );
 
@@ -144,7 +144,7 @@ static function ( $classes ) {
 // Preload server-registered block schemas.
 wp_add_inline_script(
 	'wp-blocks',
-	'wp.blocks.unstable__bootstrapServerSideBlockDefinitions(' . wp_json_encode( get_block_editor_server_block_settings() ) . ');'
+	'wp.blocks.unstable__bootstrapServerSideBlockDefinitions(' . wp_json_encode( get_block_editor_server_block_settings(), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) . ');'
 );
 
 // Preload server-registered block bindings sources.
@@ -158,7 +158,7 @@ static function ( $classes ) {
 			'usesContext' => $source->uses_context,
 		);
 	}
-	$script = sprintf( 'for ( const source of %s ) { wp.blocks.registerBlockBindingsSource( source ); }', wp_json_encode( $filtered_sources ) );
+	$script = sprintf( 'for ( const source of %s ) { wp.blocks.registerBlockBindingsSource( source ); }', wp_json_encode( $filtered_sources, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) );
 	wp_add_inline_script(
 		'wp-blocks',
 		$script
@@ -178,7 +178,7 @@ static function ( $classes ) {
 );
 wp_add_inline_script(
 	'wp-editor',
-	sprintf( 'var _wpMetaBoxUrl = %s;', wp_json_encode( $meta_box_url ) ),
+	sprintf( 'var _wpMetaBoxUrl = %s;', wp_json_encode( $meta_box_url, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ),
 	'before'
 );
 
@@ -364,8 +364,8 @@ static function ( $classes ) {
 	$init_script,
 	$post->post_type,
 	$post->ID,
-	wp_json_encode( $editor_settings ),
-	wp_json_encode( $initial_edits )
+	wp_json_encode( $editor_settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+	wp_json_encode( $initial_edits, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 );
 wp_add_inline_script( 'wp-edit-post', $script );
 
diff --git a/src/wp-admin/includes/class-wp-internal-pointers.php b/src/wp-admin/includes/class-wp-internal-pointers.php
index 6d7ebe958087a..09dc56ae3528e 100644
--- a/src/wp-admin/includes/class-wp-internal-pointers.php
+++ b/src/wp-admin/includes/class-wp-internal-pointers.php
@@ -120,7 +120,7 @@ private static function print_js( $pointer_id, $selector, $args ) {
 		?>
 		<script type="text/javascript">
 		(function($){
-			var options = <?php echo wp_json_encode( $args ); ?>, setup;
+			var options = <?php echo wp_json_encode( $args, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ); ?>, setup;
 
 			if ( ! options )
 				return;
diff --git a/src/wp-admin/includes/class-wp-list-table.php b/src/wp-admin/includes/class-wp-list-table.php
index 4b6a82a98ec0a..6568b1563bef4 100644
--- a/src/wp-admin/includes/class-wp-list-table.php
+++ b/src/wp-admin/includes/class-wp-list-table.php
@@ -1871,6 +1871,6 @@ public function _js_vars() {
 			),
 		);
 
-		printf( "<script type='text/javascript'>list_args = %s;</script>\n", wp_json_encode( $args ) );
+		printf( "<script type='text/javascript'>list_args = %s;</script>\n", wp_json_encode( $args, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) );
 	}
 }
diff --git a/src/wp-admin/includes/class-wp-privacy-policy-content.php b/src/wp-admin/includes/class-wp-privacy-policy-content.php
index 16fe3a689a0b9..c505df9b81644 100644
--- a/src/wp-admin/includes/class-wp-privacy-policy-content.php
+++ b/src/wp-admin/includes/class-wp-privacy-policy-content.php
@@ -348,7 +348,7 @@ public static function notice( $post = null ) {
 				sprintf(
 					'wp.data.dispatch( "core/notices" ).createWarningNotice( "%s", { actions: [ %s ], isDismissible: false } )',
 					$message,
-					wp_json_encode( $action )
+					wp_json_encode( $action, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 				),
 				'after'
 			);
diff --git a/src/wp-admin/includes/class-wp-themes-list-table.php b/src/wp-admin/includes/class-wp-themes-list-table.php
index b17fb912d26dc..d7c491bd1c79e 100644
--- a/src/wp-admin/includes/class-wp-themes-list-table.php
+++ b/src/wp-admin/includes/class-wp-themes-list-table.php
@@ -357,7 +357,7 @@ public function _js_vars( $extra_args = array() ) {
 			$args = array_merge( $args, $extra_args );
 		}
 
-		printf( "<script type='text/javascript'>var theme_list_args = %s;</script>\n", wp_json_encode( $args ) );
+		printf( "<script type='text/javascript'>var theme_list_args = %s;</script>\n", wp_json_encode( $args, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) );
 		parent::_js_vars();
 	}
 }
diff --git a/src/wp-admin/includes/media.php b/src/wp-admin/includes/media.php
index 22164aa65a72c..5fda1d9de2733 100644
--- a/src/wp-admin/includes/media.php
+++ b/src/wp-admin/includes/media.php
@@ -274,7 +274,7 @@ function media_send_to_editor( $html ) {
 	?>
 	<script type="text/javascript">
 	var win = window.dialogArguments || opener || parent || top;
-	win.send_to_editor( <?php echo wp_json_encode( $html ); ?> );
+	win.send_to_editor( <?php echo wp_json_encode( $html, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ); ?> );
 	</script>
 	<?php
 	exit;
@@ -2236,7 +2236,7 @@ function media_upload_form( $errors = null ) {
 
 	?>
 	var resize_height = <?php echo $large_size_h; ?>, resize_width = <?php echo $large_size_w; ?>,
-	wpUploaderInit = <?php echo wp_json_encode( $plupload_init ); ?>;
+	wpUploaderInit = <?php echo wp_json_encode( $plupload_init, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ); ?>;
 	</script>
 
 	<div id="plupload-upload-ui" class="hide-if-no-js">
diff --git a/src/wp-admin/includes/misc.php b/src/wp-admin/includes/misc.php
index c818dd8698a3b..8719378a35f62 100644
--- a/src/wp-admin/includes/misc.php
+++ b/src/wp-admin/includes/misc.php
@@ -1085,7 +1085,7 @@ function wp_color_scheme_settings() {
 		);
 	}
 
-	echo '<script type="text/javascript">var _wpColorScheme = ' . wp_json_encode( array( 'icons' => $icon_colors ) ) . ";</script>\n";
+	echo '<script type="text/javascript">var _wpColorScheme = ' . wp_json_encode( array( 'icons' => $icon_colors ), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) . ";</script>\n";
 }
 
 /**
diff --git a/src/wp-admin/includes/options.php b/src/wp-admin/includes/options.php
index 2ede58cfa3554..f4a44e57f234a 100644
--- a/src/wp-admin/includes/options.php
+++ b/src/wp-admin/includes/options.php
@@ -37,7 +37,7 @@ function options_general_add_js() {
 	jQuery( function($) {
 		var $siteName = $( '#wp-admin-bar-site-name' ).children( 'a' ).first(),
 			$siteIconPreview = $('#site-icon-preview-site-title'),
-			homeURL = ( <?php echo wp_json_encode( get_home_url() ); ?> || '' ).replace( /^(https?:\/\/)?(www\.)?/, '' );
+			homeURL = ( <?php echo wp_json_encode( get_home_url(), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ); ?> || '' ).replace( /^(https?:\/\/)?(www\.)?/, '' );
 
 		$( '#blogname' ).on( 'input', function() {
 			var title = $.trim( $( this ).val() ) || homeURL;
diff --git a/src/wp-admin/includes/post.php b/src/wp-admin/includes/post.php
index ebdd61df345dc..0163008d17eed 100644
--- a/src/wp-admin/includes/post.php
+++ b/src/wp-admin/includes/post.php
@@ -2442,7 +2442,7 @@ function the_block_editor_meta_boxes() {
 	 * our editor instance.
 	 */
 	$script = 'window._wpLoadBlockEditor.then( function() {
-		wp.data.dispatch( \'core/edit-post\' ).setAvailableMetaBoxesPerLocation( ' . wp_json_encode( $meta_boxes_per_location ) . ' );
+		wp.data.dispatch( \'core/edit-post\' ).setAvailableMetaBoxesPerLocation( ' . wp_json_encode( $meta_boxes_per_location, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) . ' );
 	} );';
 
 	wp_add_inline_script( 'wp-edit-post', $script );
diff --git a/src/wp-admin/includes/template.php b/src/wp-admin/includes/template.php
index d8ee91d7ecaab..a2eb7dc1ad215 100644
--- a/src/wp-admin/includes/template.php
+++ b/src/wp-admin/includes/template.php
@@ -2479,7 +2479,7 @@ function get_media_states( $post ) {
 function compression_test() {
 	?>
 	<script type="text/javascript">
-	var compressionNonce = <?php echo wp_json_encode( wp_create_nonce( 'update_can_compress_scripts' ) ); ?>;
+	var compressionNonce = <?php echo wp_json_encode( wp_create_nonce( 'update_can_compress_scripts' ), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ); ?>;
 	var testCompression = {
 		get : function(test) {
 			var x;
diff --git a/src/wp-admin/plugin-editor.php b/src/wp-admin/plugin-editor.php
index dd51aef686b58..c920eb61b7b2f 100644
--- a/src/wp-admin/plugin-editor.php
+++ b/src/wp-admin/plugin-editor.php
@@ -160,7 +160,7 @@
 	'codeEditor' => wp_enqueue_code_editor( array( 'file' => $real_file ) ),
 );
 wp_enqueue_script( 'wp-theme-plugin-editor' );
-wp_add_inline_script( 'wp-theme-plugin-editor', sprintf( 'jQuery( function( $ ) { wp.themePluginEditor.init( $( "#template" ), %s ); } )', wp_json_encode( $settings ) ) );
+wp_add_inline_script( 'wp-theme-plugin-editor', sprintf( 'jQuery( function( $ ) { wp.themePluginEditor.init( $( "#template" ), %s ); } )', wp_json_encode( $settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ) );
 wp_add_inline_script( 'wp-theme-plugin-editor', sprintf( 'wp.themePluginEditor.themeOrPlugin = "plugin";' ) );
 
 require_once ABSPATH . 'wp-admin/admin-header.php';
diff --git a/src/wp-admin/site-editor.php b/src/wp-admin/site-editor.php
index dba0c5981b91e..b0bb4e2bb1c10 100644
--- a/src/wp-admin/site-editor.php
+++ b/src/wp-admin/site-editor.php
@@ -257,14 +257,14 @@ static function ( $classes ) {
 		'wp.domReady( function() {
 			wp.editSite.initializeEditor( "site-editor", %s );
 		} );',
-		wp_json_encode( $editor_settings )
+		wp_json_encode( $editor_settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 	)
 );
 
 // Preload server-registered block schemas.
 wp_add_inline_script(
 	'wp-blocks',
-	'wp.blocks.unstable__bootstrapServerSideBlockDefinitions(' . wp_json_encode( get_block_editor_server_block_settings() ) . ');'
+	'wp.blocks.unstable__bootstrapServerSideBlockDefinitions(' . wp_json_encode( get_block_editor_server_block_settings(), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) . ');'
 );
 
 // Preload server-registered block bindings sources.
@@ -278,7 +278,7 @@ static function ( $classes ) {
 			'usesContext' => $source->uses_context,
 		);
 	}
-	$script = sprintf( 'for ( const source of %s ) { wp.blocks.registerBlockBindingsSource( source ); }', wp_json_encode( $filtered_sources ) );
+	$script = sprintf( 'for ( const source of %s ) { wp.blocks.registerBlockBindingsSource( source ); }', wp_json_encode( $filtered_sources, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) );
 	wp_add_inline_script(
 		'wp-blocks',
 		$script
@@ -287,7 +287,7 @@ static function ( $classes ) {
 
 wp_add_inline_script(
 	'wp-blocks',
-	sprintf( 'wp.blocks.setCategories( %s );', wp_json_encode( isset( $editor_settings['blockCategories'] ) ? $editor_settings['blockCategories'] : array() ) ),
+	sprintf( 'wp.blocks.setCategories( %s );', wp_json_encode( isset( $editor_settings['blockCategories'] ) ? $editor_settings['blockCategories'] : array(), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ),
 	'after'
 );
 
diff --git a/src/wp-admin/theme-editor.php b/src/wp-admin/theme-editor.php
index fbb9b6bd94fb5..e7fd3fa88b8e5 100644
--- a/src/wp-admin/theme-editor.php
+++ b/src/wp-admin/theme-editor.php
@@ -146,7 +146,7 @@
 	'codeEditor' => wp_enqueue_code_editor( compact( 'file' ) ),
 );
 wp_enqueue_script( 'wp-theme-plugin-editor' );
-wp_add_inline_script( 'wp-theme-plugin-editor', sprintf( 'jQuery( function( $ ) { wp.themePluginEditor.init( $( "#template" ), %s ); } )', wp_json_encode( $settings ) ) );
+wp_add_inline_script( 'wp-theme-plugin-editor', sprintf( 'jQuery( function( $ ) { wp.themePluginEditor.init( $( "#template" ), %s ); } )', wp_json_encode( $settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ) );
 wp_add_inline_script( 'wp-theme-plugin-editor', 'wp.themePluginEditor.themeOrPlugin = "theme";' );
 
 require_once ABSPATH . 'wp-admin/admin-header.php';
diff --git a/src/wp-admin/widgets-form-blocks.php b/src/wp-admin/widgets-form-blocks.php
index 0d161cf526d50..c8cf44d8190f1 100644
--- a/src/wp-admin/widgets-form-blocks.php
+++ b/src/wp-admin/widgets-form-blocks.php
@@ -41,14 +41,14 @@
 		'wp.domReady( function() {
 			wp.editWidgets.initialize( "widgets-editor", %s );
 		} );',
-		wp_json_encode( $editor_settings )
+		wp_json_encode( $editor_settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 	)
 );
 
 // Preload server-registered block schemas.
 wp_add_inline_script(
 	'wp-blocks',
-	'wp.blocks.unstable__bootstrapServerSideBlockDefinitions(' . wp_json_encode( get_block_editor_server_block_settings() ) . ');'
+	'wp.blocks.unstable__bootstrapServerSideBlockDefinitions(' . wp_json_encode( get_block_editor_server_block_settings(), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) . ');'
 );
 
 // Preload server-registered block bindings sources.
@@ -62,7 +62,7 @@
 			'usesContext' => $source->uses_context,
 		);
 	}
-	$script = sprintf( 'for ( const source of %s ) { wp.blocks.registerBlockBindingsSource( source ); }', wp_json_encode( $filtered_sources ) );
+	$script = sprintf( 'for ( const source of %s ) { wp.blocks.registerBlockBindingsSource( source ); }', wp_json_encode( $filtered_sources, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) );
 	wp_add_inline_script(
 		'wp-blocks',
 		$script
@@ -71,7 +71,7 @@
 
 wp_add_inline_script(
 	'wp-blocks',
-	sprintf( 'wp.blocks.setCategories( %s );', wp_json_encode( get_block_categories( $block_editor_context ) ) ),
+	sprintf( 'wp.blocks.setCategories( %s );', wp_json_encode( get_block_categories( $block_editor_context ), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ),
 	'after'
 );
 
diff --git a/src/wp-content/themes/twentytwenty/functions.php b/src/wp-content/themes/twentytwenty/functions.php
index a966f1bda719c..1a5c512f8b177 100644
--- a/src/wp-content/themes/twentytwenty/functions.php
+++ b/src/wp-content/themes/twentytwenty/functions.php
@@ -684,8 +684,8 @@ function twentytwenty_customize_preview_init() {
 		'twentytwenty-customize-preview',
 		sprintf(
 			'wp.customize.selectiveRefresh.partialConstructor[ %1$s ].prototype.attrs = %2$s;',
-			wp_json_encode( 'cover_opacity' ),
-			wp_json_encode( twentytwenty_customize_opacity_range() )
+			wp_json_encode( 'cover_opacity', JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+			wp_json_encode( twentytwenty_customize_opacity_range(), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 		)
 	);
 }
diff --git a/src/wp-includes/class-wp-customize-manager.php b/src/wp-includes/class-wp-customize-manager.php
index 6a656808ae5a1..0a8c743019d80 100644
--- a/src/wp-includes/class-wp-customize-manager.php
+++ b/src/wp-includes/class-wp-customize-manager.php
@@ -476,7 +476,7 @@ protected function wp_die( $ajax_message, $message = null ) {
 			( function( api, settings ) {
 				var preview = new api.Messenger( settings.messengerArgs );
 				preview.send( 'iframe-loading-error', settings.error );
-			} )( wp.customize, <?php echo wp_json_encode( $settings ); ?> );
+			} )( wp.customize, <?php echo wp_json_encode( $settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ); ?> );
 			</script>
 			<?php
 			$message .= wp_get_inline_script_tag( wp_remove_surrounding_empty_script_tags( ob_get_clean() ) );
@@ -2205,7 +2205,7 @@ public function customize_preview_settings() {
 		ob_start();
 		?>
 		<script>
-			var _wpCustomizeSettings = <?php echo wp_json_encode( $settings ); ?>;
+			var _wpCustomizeSettings = <?php echo wp_json_encode( $settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ); ?>;
 			_wpCustomizeSettings.values = {};
 			(function( v ) {
 				<?php
@@ -2218,8 +2218,8 @@ public function customize_preview_settings() {
 					if ( $setting->check_capabilities() ) {
 						printf(
 							"v[%s] = %s;\n",
-							wp_json_encode( $id ),
-							wp_json_encode( $setting->js_value() )
+							wp_json_encode( $id, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+							wp_json_encode( $setting->js_value(), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 						);
 					}
 				}
@@ -4988,7 +4988,7 @@ public function customize_pane_settings() {
 		ob_start();
 		?>
 		<script>
-			var _wpCustomizeSettings = <?php echo wp_json_encode( $settings ); ?>;
+			var _wpCustomizeSettings = <?php echo wp_json_encode( $settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ); ?>;
 			_wpCustomizeSettings.initialClientTimestamp = _.now();
 			_wpCustomizeSettings.controls = {};
 			_wpCustomizeSettings.settings = {};
@@ -5000,8 +5000,8 @@ public function customize_pane_settings() {
 				if ( $setting->check_capabilities() ) {
 					printf(
 						"s[%s] = %s;\n",
-						wp_json_encode( $setting->id ),
-						wp_json_encode( $setting->json() )
+						wp_json_encode( $setting->id, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+						wp_json_encode( $setting->json(), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 					);
 				}
 			}
@@ -5013,8 +5013,8 @@ public function customize_pane_settings() {
 				if ( $control->check_capabilities() ) {
 					printf(
 						"c[%s] = %s;\n",
-						wp_json_encode( $control->id ),
-						wp_json_encode( $control->json() )
+						wp_json_encode( $control->id, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+						wp_json_encode( $control->json(), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 					);
 				}
 			}
diff --git a/src/wp-includes/class-wp-customize-nav-menus.php b/src/wp-includes/class-wp-customize-nav-menus.php
index f6d1c5af9e6e1..3650146241f50 100644
--- a/src/wp-includes/class-wp-customize-nav-menus.php
+++ b/src/wp-includes/class-wp-customize-nav-menus.php
@@ -545,7 +545,7 @@ public function enqueue_scripts() {
 			'locationSlugMappedToName' => get_registered_nav_menus(),
 		);
 
-		$data = sprintf( 'var _wpCustomizeNavMenusSettings = %s;', wp_json_encode( $settings ) );
+		$data = sprintf( 'var _wpCustomizeNavMenusSettings = %s;', wp_json_encode( $settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) );
 		wp_scripts()->add_data( 'customize-nav-menus', 'data', $data );
 
 		// This is copied from nav-menus.php, and it has an unfortunate object name of `menus`.
@@ -1548,7 +1548,7 @@ public function export_preview_data() {
 		$exports = array(
 			'navMenuInstanceArgs' => $this->preview_nav_menu_instance_args,
 		);
-		wp_print_inline_script_tag( sprintf( 'var _wpCustomizePreviewNavMenusExports = %s;', wp_json_encode( $exports ) ) );
+		wp_print_inline_script_tag( sprintf( 'var _wpCustomizePreviewNavMenusExports = %s;', wp_json_encode( $exports, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ) );
 	}
 
 	/**
diff --git a/src/wp-includes/class-wp-customize-widgets.php b/src/wp-includes/class-wp-customize-widgets.php
index b24a9c8b4723f..f9a428dd537fc 100644
--- a/src/wp-includes/class-wp-customize-widgets.php
+++ b/src/wp-includes/class-wp-customize-widgets.php
@@ -832,7 +832,7 @@ public function enqueue_scripts() {
 		$wp_scripts->add_data(
 			'customize-widgets',
 			'data',
-			sprintf( 'var _wpCustomizeWidgetsSettings = %s;', wp_json_encode( $settings ) )
+			sprintf( 'var _wpCustomizeWidgetsSettings = %s;', wp_json_encode( $settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) )
 		);
 
 		/*
@@ -859,14 +859,14 @@ public function enqueue_scripts() {
 					'wp.domReady( function() {
 					   wp.customizeWidgets.initialize( "widgets-customizer", %s );
 					} );',
-					wp_json_encode( $editor_settings )
+					wp_json_encode( $editor_settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 				)
 			);
 
 			// Preload server-registered block schemas.
 			wp_add_inline_script(
 				'wp-blocks',
-				'wp.blocks.unstable__bootstrapServerSideBlockDefinitions(' . wp_json_encode( get_block_editor_server_block_settings() ) . ');'
+				'wp.blocks.unstable__bootstrapServerSideBlockDefinitions(' . wp_json_encode( get_block_editor_server_block_settings(), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) . ');'
 			);
 
 			// Preload server-registered block bindings sources.
@@ -880,7 +880,7 @@ public function enqueue_scripts() {
 						'usesContext' => $source->uses_context,
 					);
 				}
-				$script = sprintf( 'for ( const source of %s ) { wp.blocks.registerBlockBindingsSource( source ); }', wp_json_encode( $filtered_sources ) );
+				$script = sprintf( 'for ( const source of %s ) { wp.blocks.registerBlockBindingsSource( source ); }', wp_json_encode( $filtered_sources, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) );
 				wp_add_inline_script(
 					'wp-blocks',
 					$script
@@ -889,7 +889,7 @@ public function enqueue_scripts() {
 
 			wp_add_inline_script(
 				'wp-blocks',
-				sprintf( 'wp.blocks.setCategories( %s );', wp_json_encode( get_block_categories( $block_editor_context ) ) ),
+				sprintf( 'wp.blocks.setCategories( %s );', wp_json_encode( get_block_categories( $block_editor_context ), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ),
 				'after'
 			);
 
@@ -1334,7 +1334,7 @@ public function export_preview_data() {
 			unset( $registered_widget['callback'] ); // May not be JSON-serializable.
 		}
 		wp_print_inline_script_tag(
-			sprintf( 'var _wpWidgetCustomizerPreviewSettings = %s;', wp_json_encode( $settings ) )
+			sprintf( 'var _wpWidgetCustomizerPreviewSettings = %s;', wp_json_encode( $settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) )
 		);
 	}
 
diff --git a/src/wp-includes/class-wp-script-modules.php b/src/wp-includes/class-wp-script-modules.php
index dbfa038f8cbe2..056c061368f8b 100644
--- a/src/wp-includes/class-wp-script-modules.php
+++ b/src/wp-includes/class-wp-script-modules.php
@@ -248,7 +248,7 @@ public function print_import_map() {
 		$import_map = $this->get_import_map();
 		if ( ! empty( $import_map['imports'] ) ) {
 			wp_print_inline_script_tag(
-				wp_json_encode( $import_map, JSON_HEX_TAG | JSON_HEX_AMP ),
+				wp_json_encode( $import_map, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
 				array(
 					'type' => 'importmap',
 					'id'   => 'wp-importmap',
diff --git a/src/wp-includes/class-wp-scripts.php b/src/wp-includes/class-wp-scripts.php
index 77dff94c0497a..b1e4c76c73d43 100644
--- a/src/wp-includes/class-wp-scripts.php
+++ b/src/wp-includes/class-wp-scripts.php
@@ -596,7 +596,7 @@ public function localize( $handle, $object_name, $l10n ) {
 			}
 		}
 
-		$script = "var $object_name = " . wp_json_encode( $l10n ) . ';';
+		$script = "var $object_name = " . wp_json_encode( $l10n, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) . ';';
 
 		if ( ! empty( $after ) ) {
 			$script .= "\n$after;";
diff --git a/src/wp-includes/customize/class-wp-customize-selective-refresh.php b/src/wp-includes/customize/class-wp-customize-selective-refresh.php
index d20e8ab0a76ad..f695338657828 100644
--- a/src/wp-includes/customize/class-wp-customize-selective-refresh.php
+++ b/src/wp-includes/customize/class-wp-customize-selective-refresh.php
@@ -193,7 +193,7 @@ public function export_preview_data() {
 		);
 
 		// Export data to JS.
-		wp_print_inline_script_tag( sprintf( 'var _customizePartialRefreshExports = %s;', wp_json_encode( $exports ) ) );
+		wp_print_inline_script_tag( sprintf( 'var _customizePartialRefreshExports = %s;', wp_json_encode( $exports, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ) );
 	}
 
 	/**
diff --git a/src/wp-includes/general-template.php b/src/wp-includes/general-template.php
index 09d344dd1e8bc..adef3138fe065 100644
--- a/src/wp-includes/general-template.php
+++ b/src/wp-includes/general-template.php
@@ -4066,7 +4066,7 @@ function wp_enqueue_code_editor( $args ) {
 		}
 	}
 
-	wp_add_inline_script( 'code-editor', sprintf( 'jQuery.extend( wp.codeEditor.defaultSettings, %s );', wp_json_encode( $settings ) ) );
+	wp_add_inline_script( 'code-editor', sprintf( 'jQuery.extend( wp.codeEditor.defaultSettings, %s );', wp_json_encode( $settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ) );
 
 	/**
 	 * Fires when scripts and styles are enqueued for the code editor.
diff --git a/src/wp-includes/media.php b/src/wp-includes/media.php
index 494ee613dd138..cffb5eb68ce96 100644
--- a/src/wp-includes/media.php
+++ b/src/wp-includes/media.php
@@ -3274,7 +3274,7 @@ function wp_playlist_shortcode( $attr ) {
 		?>
 	</ol>
 	</noscript>
-	<script type="application/json" class="wp-playlist-script"><?php echo wp_json_encode( $data ); ?></script>
+	<script type="application/json" class="wp-playlist-script"><?php echo wp_json_encode( $data, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ); ?></script>
 </div>
 	<?php
 	return ob_get_clean();
@@ -4435,7 +4435,7 @@ function wp_plupload_default_settings() {
 		'limitExceeded' => is_multisite() && ! is_upload_space_available(),
 	);
 
-	$script = 'var _wpPluploadSettings = ' . wp_json_encode( $settings ) . ';';
+	$script = 'var _wpPluploadSettings = ' . wp_json_encode( $settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) . ';';
 
 	if ( $data ) {
 		$script = "$data\n$script";
diff --git a/src/wp-includes/script-loader.php b/src/wp-includes/script-loader.php
index 54193c841c7c3..def31178880d5 100644
--- a/src/wp-includes/script-loader.php
+++ b/src/wp-includes/script-loader.php
@@ -159,7 +159,8 @@ function wp_default_packages_vendor( $scripts ) {
 						'LLL'  => __( 'F j, Y g:i a' ),
 						'LLLL' => null,
 					),
-				)
+				),
+				JSON_HEX_TAG | JSON_UNESCAPED_SLASHES
 			)
 		),
 		'after'
@@ -384,7 +385,7 @@ function wp_default_packages_inline_scripts( $scripts ) {
 				var preferencesStore = wp.preferences.store;
 				wp.data.dispatch( preferencesStore ).setPersistenceLayer( persistenceLayer );
 			} ) ();',
-			wp_json_encode( $preload_data ),
+			wp_json_encode( $preload_data, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
 			$user_id
 		)
 	);
@@ -477,7 +478,8 @@ function wp_default_packages_inline_scripts( $scripts ) {
 						'string'          => $timezone_string,
 						'abbr'            => $timezone_abbr,
 					),
-				)
+				),
+				JSON_HEX_TAG | JSON_UNESCAPED_SLASHES
 			)
 		),
 		'after'
@@ -640,7 +642,7 @@ function wp_tinymce_inline_scripts() {
 
 	$script = 'window.wpEditorL10n = {
 		tinymce: {
-			baseURL: ' . wp_json_encode( includes_url( 'js/tinymce' ) ) . ',
+			baseURL: ' . wp_json_encode( includes_url( 'js/tinymce' ), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) . ',
 			suffix: ' . ( SCRIPT_DEBUG ? '""' : '".min"' ) . ',
 			settings: ' . $init_obj . ',
 		}
@@ -1155,7 +1157,8 @@ function wp_default_scripts( $scripts ) {
 						'mejs.welsh'               => __( 'Welsh' ),
 						'mejs.yiddish'             => __( 'Yiddish' ),
 					),
-				)
+				),
+				JSON_HEX_TAG | JSON_UNESCAPED_SLASHES
 			)
 		),
 		'before'
@@ -1999,7 +2002,8 @@ function wp_localize_jquery_ui_datepicker() {
 			'dateFormat'      => $datepicker_date_format,
 			'firstDay'        => absint( get_option( 'start_of_week' ) ),
 			'isRTL'           => $wp_locale->is_rtl(),
-		)
+		),
+		JSON_HEX_TAG | JSON_UNESCAPED_SLASHES
 	);
 
 	wp_add_inline_script( 'jquery-ui-datepicker', "jQuery(function(jQuery){jQuery.datepicker.setDefaults({$datepicker_defaults});});" );
@@ -2809,7 +2813,7 @@ function enqueue_editor_block_styles_assets() {
 			$register_script_lines[] = sprintf(
 				'	wp.blocks.registerBlockStyle( \'%s\', %s );',
 				$block_name,
-				wp_json_encode( $block_style )
+				wp_json_encode( $block_style, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			);
 		}
 	}
diff --git a/src/wp-includes/speculative-loading.php b/src/wp-includes/speculative-loading.php
index 2a06bc4aea03a..319e04d36ddde 100644
--- a/src/wp-includes/speculative-loading.php
+++ b/src/wp-includes/speculative-loading.php
@@ -247,7 +247,8 @@ function wp_print_speculation_rules(): void {
 
 	wp_print_inline_script_tag(
 		(string) wp_json_encode(
-			$speculation_rules
+			$speculation_rules,
+			JSON_HEX_TAG | JSON_UNESCAPED_SLASHES
 		),
 		array( 'type' => 'speculationrules' )
 	);
diff --git a/src/wp-includes/theme-previews.php b/src/wp-includes/theme-previews.php
index 7e0c085b1c102..8297dca0a2a70 100644
--- a/src/wp-includes/theme-previews.php
+++ b/src/wp-includes/theme-previews.php
@@ -49,7 +49,7 @@ function wp_attach_theme_preview_middleware() {
 		'wp-api-fetch',
 		sprintf(
 			'wp.apiFetch.use( wp.apiFetch.createThemePreviewMiddleware( %s ) );',
-			wp_json_encode( sanitize_text_field( wp_unslash( $_GET['wp_theme_preview'] ) ) )
+			wp_json_encode( sanitize_text_field( wp_unslash( $_GET['wp_theme_preview'] ) ), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 		),
 		'after'
 	);
@@ -70,7 +70,7 @@ function wp_block_theme_activate_nonce() {
 	$nonce_handle = 'switch-theme_' . wp_get_theme_preview_path();
 	?>
 	<script type="text/javascript">
-		window.WP_BLOCK_THEME_ACTIVATE_NONCE = <?php echo wp_json_encode( wp_create_nonce( $nonce_handle ) ); ?>;
+		window.WP_BLOCK_THEME_ACTIVATE_NONCE = <?php echo wp_json_encode( wp_create_nonce( $nonce_handle ), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ); ?>;
 	</script>
 	<?php
 }
diff --git a/src/wp-includes/theme.php b/src/wp-includes/theme.php
index 6287edef40110..8e1029780a5c0 100644
--- a/src/wp-includes/theme.php
+++ b/src/wp-includes/theme.php
@@ -3748,7 +3748,7 @@ function _wp_customize_loader_settings() {
 		),
 	);
 
-	$script = 'var _wpCustomizeLoaderSettings = ' . wp_json_encode( $settings ) . ';';
+	$script = 'var _wpCustomizeLoaderSettings = ' . wp_json_encode( $settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) . ';';
 
 	$wp_scripts = wp_scripts();
 	$data       = $wp_scripts->get_data( 'customize-loader', 'data' );
diff --git a/src/wp-includes/widgets/class-wp-widget-custom-html.php b/src/wp-includes/widgets/class-wp-widget-custom-html.php
index 0474e89bb2ec9..bdae2dd38eaa3 100644
--- a/src/wp-includes/widgets/class-wp-widget-custom-html.php
+++ b/src/wp-includes/widgets/class-wp-widget-custom-html.php
@@ -215,14 +215,14 @@ public function enqueue_admin_scripts() {
 		);
 
 		wp_enqueue_script( 'custom-html-widgets' );
-		wp_add_inline_script( 'custom-html-widgets', sprintf( 'wp.customHtmlWidgets.idBases.push( %s );', wp_json_encode( $this->id_base ) ) );
+		wp_add_inline_script( 'custom-html-widgets', sprintf( 'wp.customHtmlWidgets.idBases.push( %s );', wp_json_encode( $this->id_base, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ) );
 
 		if ( empty( $settings ) ) {
 			$settings = array(
 				'disabled' => true,
 			);
 		}
-		wp_add_inline_script( 'custom-html-widgets', sprintf( 'wp.customHtmlWidgets.init( %s );', wp_json_encode( $settings ) ), 'after' );
+		wp_add_inline_script( 'custom-html-widgets', sprintf( 'wp.customHtmlWidgets.init( %s );', wp_json_encode( $settings, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ), 'after' );
 
 		$l10n = array(
 			'errorNotice' => array(
@@ -233,7 +233,7 @@ public function enqueue_admin_scripts() {
 				// @todo This is lacking, as some languages have a dedicated dual form. For proper handling of plurals in JS, see #20491.
 			),
 		);
-		wp_add_inline_script( 'custom-html-widgets', sprintf( 'jQuery.extend( wp.customHtmlWidgets.l10n, %s );', wp_json_encode( $l10n ) ), 'after' );
+		wp_add_inline_script( 'custom-html-widgets', sprintf( 'jQuery.extend( wp.customHtmlWidgets.l10n, %s );', wp_json_encode( $l10n, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ), 'after' );
 	}
 
 	/**
diff --git a/src/wp-includes/widgets/class-wp-widget-media-audio.php b/src/wp-includes/widgets/class-wp-widget-media-audio.php
index d7bffd26481b6..7a8d5253a0b31 100644
--- a/src/wp-includes/widgets/class-wp-widget-media-audio.php
+++ b/src/wp-includes/widgets/class-wp-widget-media-audio.php
@@ -160,8 +160,8 @@ public function enqueue_admin_scripts() {
 			$handle,
 			sprintf(
 				'wp.mediaWidgets.modelConstructors[ %s ].prototype.schema = %s;',
-				wp_json_encode( $this->id_base ),
-				wp_json_encode( $exported_schema )
+				wp_json_encode( $this->id_base, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+				wp_json_encode( $exported_schema, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			)
 		);
 
@@ -172,9 +172,9 @@ public function enqueue_admin_scripts() {
 					wp.mediaWidgets.controlConstructors[ %1$s ].prototype.mime_type = %2$s;
 					wp.mediaWidgets.controlConstructors[ %1$s ].prototype.l10n = _.extend( {}, wp.mediaWidgets.controlConstructors[ %1$s ].prototype.l10n, %3$s );
 				',
-				wp_json_encode( $this->id_base ),
-				wp_json_encode( $this->widget_options['mime_type'] ),
-				wp_json_encode( $this->l10n )
+				wp_json_encode( $this->id_base, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+				wp_json_encode( $this->widget_options['mime_type'], JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+				wp_json_encode( $this->l10n, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			)
 		);
 	}
diff --git a/src/wp-includes/widgets/class-wp-widget-media-gallery.php b/src/wp-includes/widgets/class-wp-widget-media-gallery.php
index a2527a6554231..9f76bc87106f1 100644
--- a/src/wp-includes/widgets/class-wp-widget-media-gallery.php
+++ b/src/wp-includes/widgets/class-wp-widget-media-gallery.php
@@ -148,8 +148,8 @@ public function enqueue_admin_scripts() {
 			$handle,
 			sprintf(
 				'wp.mediaWidgets.modelConstructors[ %s ].prototype.schema = %s;',
-				wp_json_encode( $this->id_base ),
-				wp_json_encode( $exported_schema )
+				wp_json_encode( $this->id_base, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+				wp_json_encode( $exported_schema, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			)
 		);
 
@@ -160,9 +160,9 @@ public function enqueue_admin_scripts() {
 					wp.mediaWidgets.controlConstructors[ %1$s ].prototype.mime_type = %2$s;
 					_.extend( wp.mediaWidgets.controlConstructors[ %1$s ].prototype.l10n, %3$s );
 				',
-				wp_json_encode( $this->id_base ),
-				wp_json_encode( $this->widget_options['mime_type'] ),
-				wp_json_encode( $this->l10n )
+				wp_json_encode( $this->id_base, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+				wp_json_encode( $this->widget_options['mime_type'], JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+				wp_json_encode( $this->l10n, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			)
 		);
 	}
diff --git a/src/wp-includes/widgets/class-wp-widget-media-image.php b/src/wp-includes/widgets/class-wp-widget-media-image.php
index b76536f7b2e1c..5977eb347c731 100644
--- a/src/wp-includes/widgets/class-wp-widget-media-image.php
+++ b/src/wp-includes/widgets/class-wp-widget-media-image.php
@@ -323,8 +323,8 @@ public function enqueue_admin_scripts() {
 			$handle,
 			sprintf(
 				'wp.mediaWidgets.modelConstructors[ %s ].prototype.schema = %s;',
-				wp_json_encode( $this->id_base ),
-				wp_json_encode( $exported_schema )
+				wp_json_encode( $this->id_base, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+				wp_json_encode( $exported_schema, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			)
 		);
 
@@ -335,9 +335,9 @@ public function enqueue_admin_scripts() {
 					wp.mediaWidgets.controlConstructors[ %1$s ].prototype.mime_type = %2$s;
 					wp.mediaWidgets.controlConstructors[ %1$s ].prototype.l10n = _.extend( {}, wp.mediaWidgets.controlConstructors[ %1$s ].prototype.l10n, %3$s );
 				',
-				wp_json_encode( $this->id_base ),
-				wp_json_encode( $this->widget_options['mime_type'] ),
-				wp_json_encode( $this->l10n )
+				wp_json_encode( $this->id_base, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+				wp_json_encode( $this->widget_options['mime_type'], JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+				wp_json_encode( $this->l10n, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			)
 		);
 	}
diff --git a/src/wp-includes/widgets/class-wp-widget-media-video.php b/src/wp-includes/widgets/class-wp-widget-media-video.php
index fafb45f005df4..ad80f7d9d1c81 100644
--- a/src/wp-includes/widgets/class-wp-widget-media-video.php
+++ b/src/wp-includes/widgets/class-wp-widget-media-video.php
@@ -199,8 +199,8 @@ public function enqueue_admin_scripts() {
 			$handle,
 			sprintf(
 				'wp.mediaWidgets.modelConstructors[ %s ].prototype.schema = %s;',
-				wp_json_encode( $this->id_base ),
-				wp_json_encode( $exported_schema )
+				wp_json_encode( $this->id_base, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+				wp_json_encode( $exported_schema, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			)
 		);
 
@@ -211,9 +211,9 @@ public function enqueue_admin_scripts() {
 					wp.mediaWidgets.controlConstructors[ %1$s ].prototype.mime_type = %2$s;
 					wp.mediaWidgets.controlConstructors[ %1$s ].prototype.l10n = _.extend( {}, wp.mediaWidgets.controlConstructors[ %1$s ].prototype.l10n, %3$s );
 				',
-				wp_json_encode( $this->id_base ),
-				wp_json_encode( $this->widget_options['mime_type'] ),
-				wp_json_encode( $this->l10n )
+				wp_json_encode( $this->id_base, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+				wp_json_encode( $this->widget_options['mime_type'], JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
+				wp_json_encode( $this->l10n, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			)
 		);
 	}
diff --git a/src/wp-includes/widgets/class-wp-widget-text.php b/src/wp-includes/widgets/class-wp-widget-text.php
index ba6c4fdfee0be..707c5f6e9c3e0 100644
--- a/src/wp-includes/widgets/class-wp-widget-text.php
+++ b/src/wp-includes/widgets/class-wp-widget-text.php
@@ -435,7 +435,7 @@ public function enqueue_admin_scripts() {
 		wp_enqueue_editor();
 		wp_enqueue_media();
 		wp_enqueue_script( 'text-widgets' );
-		wp_add_inline_script( 'text-widgets', sprintf( 'wp.textWidgets.idBases.push( %s );', wp_json_encode( $this->id_base ) ) );
+		wp_add_inline_script( 'text-widgets', sprintf( 'wp.textWidgets.idBases.push( %s );', wp_json_encode( $this->id_base, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ) ) );
 		wp_add_inline_script( 'text-widgets', 'wp.textWidgets.init();', 'after' );
 	}
 
diff --git a/tests/phpunit/tests/dependencies/wpLocalizeScript.php b/tests/phpunit/tests/dependencies/wpLocalizeScript.php
index ed79d3e7bd5db..a57754973cf40 100644
--- a/tests/phpunit/tests/dependencies/wpLocalizeScript.php
+++ b/tests/phpunit/tests/dependencies/wpLocalizeScript.php
@@ -3,7 +3,7 @@
  * @group dependencies
  * @group scripts
  */
-class Tests_Dependencies_LocalizeScript extends WP_UnitTestCase {
+class Tests_Dependencies_wpLocalizeScript extends WP_UnitTestCase {
 	/**
 	 * @var WP_Scripts
 	 */
@@ -38,4 +38,27 @@ public function test_wp_localize_script_works_before_enqueue_script() {
 			)
 		);
 	}
+
+	/**
+	 * Verifies that wp_localize_script() outputs safe JSON whe harmful data is provided.
+	 *
+	 * @ticket 63851
+	 * @covers ::wp_localize_script
+	 */
+	public function test_wp_localize_script_outputs_safe_json() {
+		add_theme_support( 'html5', array( 'script' ) );
+
+		$path     = '/test.js';
+		$base_url = site_url( $path );
+
+		wp_enqueue_script( 'test-script', $path, array(), null );
+		wp_localize_script( 'test-script', 'testData', array( '<!--' => '<script>' ) );
+
+		$output = get_echo( 'wp_print_scripts' );
+
+		$expected  = "<script id=\"test-script-js-extra\">\nvar testData = {\"\\u003C!--\":\"\\u003Cscript\\u003E\"};\n</script>\n";
+		$expected .= "<script src=\"{$base_url}\" id=\"test-script-js\"></script>\n";
+
+		$this->assertEqualHTML( $expected, $output );
+	}
 }