diff --git a/superset-frontend/src/features/themes/ThemeModal.test.tsx b/superset-frontend/src/features/themes/ThemeModal.test.tsx
index 2e5d1a51655..4994863b074 100644
--- a/superset-frontend/src/features/themes/ThemeModal.test.tsx
+++ b/superset-frontend/src/features/themes/ThemeModal.test.tsx
@@ -17,11 +17,12 @@
  * under the License.
  */
 
-import { render, screen } from 'spec/helpers/testing-library';
+import { render, screen, waitFor } from 'spec/helpers/testing-library';
 import userEvent from '@testing-library/user-event';
 import fetchMock from 'fetch-mock';
 import ThemeModal from './ThemeModal';
 import { ThemeObject } from './types';
+import { validateTheme } from 'src/theme/utils/themeStructureValidation';
 
 const mockThemeContext = {
   setTemporaryTheme: jest.fn(),
@@ -37,6 +38,27 @@ jest.mock('src/dashboard/util/permissionUtils', () => ({
   isUserAdmin: jest.fn(() => true),
 }));
 
+// Mock JsonEditor to avoid direct DOM manipulation in tests
+jest.mock('@superset-ui/core/components/AsyncAceEditor', () => ({
+  ...jest.requireActual('@superset-ui/core/components/AsyncAceEditor'),
+  JsonEditor: ({
+    onChange,
+    value,
+    readOnly,
+  }: {
+    onChange: (value: string) => void;
+    value: string;
+    readOnly?: boolean;
+  }) => (
+    <textarea
+      data-test="json-editor"
+      value={value}
+      onChange={e => onChange(e.target.value)}
+      readOnly={readOnly}
+    />
+  ),
+}));
+
 const mockTheme: ThemeObject = {
   id: 1,
   theme_name: 'Test Theme',
@@ -89,6 +111,31 @@ afterEach(() => {
   jest.clearAllMocks();
 });
 
+// Helper to add valid JSON data to the theme
+// Uses the mocked JsonEditor textarea for testing
+const addValidJsonData = async () => {
+  const validJson = JSON.stringify(
+    { token: { colorPrimary: '#1890ff' } },
+    null,
+    2,
+  );
+  const jsonEditor = screen.getByTestId('json-editor');
+  await userEvent.clear(jsonEditor);
+  await userEvent.type(jsonEditor, validJson);
+};
+
+// Helper to add JSON with unknown tokens (triggers warnings but not errors)
+const addJsonWithUnknownToken = async () => {
+  const jsonWithUnknown = JSON.stringify(
+    { token: { colorPrimary: '#1890ff', unknownTokenName: 'value' } },
+    null,
+    2,
+  );
+  const jsonEditor = screen.getByTestId('json-editor');
+  await userEvent.clear(jsonEditor);
+  await userEvent.type(jsonEditor, jsonWithUnknown);
+};
+
 test('renders modal with add theme dialog when show is true', () => {
   render(
     <ThemeModal
@@ -283,10 +330,16 @@ test('enables save button when theme name is entered', async () => {
 
   const nameInput = screen.getByPlaceholderText('Enter theme name');
   await userEvent.type(nameInput, 'My New Theme');
+  await addValidJsonData();
 
-  const saveButton = await screen.findByRole('button', { name: 'Add' });
-
-  expect(saveButton).toBeEnabled();
+  // Wait for validation to complete and button to become enabled
+  await waitFor(
+    () => {
+      const saveButton = screen.getByRole('button', { name: 'Add' });
+      expect(saveButton).toBeEnabled();
+    },
+    { timeout: 10000 },
+  );
 });
 
 test('validates JSON format and enables save button', async () => {
@@ -304,10 +357,52 @@ test('validates JSON format and enables save button', async () => {
 
   const nameInput = screen.getByPlaceholderText('Enter theme name');
   await userEvent.type(nameInput, 'Test Theme');
+  await addValidJsonData();
 
-  const saveButton = await screen.findByRole('button', { name: 'Add' });
+  // Wait for validation to complete and button to become enabled
+  await waitFor(
+    () => {
+      const saveButton = screen.getByRole('button', { name: 'Add' });
+      expect(saveButton).toBeEnabled();
+    },
+    { timeout: 10000 },
+  );
+});
 
-  expect(saveButton).toBeEnabled();
+test('warnings do not block save - unknown tokens allow save with warnings', async () => {
+  // First verify the test data actually produces warnings (not errors)
+  const testTheme = {
+    token: { colorPrimary: '#1890ff', unknownTokenName: 'value' },
+  };
+  const validationResult = validateTheme(testTheme);
+  expect(validationResult.valid).toBe(true); // No errors
+  expect(validationResult.warnings.length).toBeGreaterThan(0); // Has warnings
+  expect(validationResult.warnings[0].tokenName).toBe('unknownTokenName');
+
+  render(
+    <ThemeModal
+      addDangerToast={jest.fn()}
+      addSuccessToast={jest.fn()}
+      onThemeAdd={jest.fn()}
+      onHide={jest.fn()}
+      show
+      canDevelop={false}
+    />,
+    { useRedux: true, useRouter: true },
+  );
+
+  const nameInput = screen.getByPlaceholderText('Enter theme name');
+  await userEvent.type(nameInput, 'Theme With Unknown Token');
+  await addJsonWithUnknownToken();
+
+  // Wait for validation to complete - button should still be enabled despite warnings
+  await waitFor(
+    () => {
+      const saveButton = screen.getByRole('button', { name: 'Add' });
+      expect(saveButton).toBeEnabled();
+    },
+    { timeout: 10000 },
+  );
 });
 
 test('shows unsaved changes alert when closing modal with modifications', async () => {
@@ -418,6 +513,19 @@ test('saves changes when clicking Save button in unsaved changes alert', async (
 
   const nameInput = screen.getByPlaceholderText('Enter theme name');
   await userEvent.type(nameInput, 'Modified Theme');
+  await addValidJsonData();
+
+  // Wait for validation to complete before canceling
+  await waitFor(
+    () => {
+      const addButton = screen.getByRole('button', { name: 'Add' });
+      expect(addButton).toBeEnabled();
+    },
+    { timeout: 10000 },
+  );
+
+  // Give extra time for all state updates to complete
+  await new Promise(resolve => setTimeout(resolve, 500));
 
   const cancelButton = screen.getByRole('button', { name: 'Cancel' });
   await userEvent.click(cancelButton);
@@ -426,13 +534,26 @@ test('saves changes when clicking Save button in unsaved changes alert', async (
     await screen.findByText('You have unsaved changes'),
   ).toBeInTheDocument();
 
-  const saveButton = screen.getByRole('button', { name: 'Save' });
+  // Wait for the Save button in the alert to be enabled
+  const saveButton = await waitFor(
+    () => {
+      const button = screen.getByRole('button', { name: 'Save' });
+      expect(button).toBeEnabled();
+      return button;
+    },
+    { timeout: 10000 },
+  );
   await userEvent.click(saveButton);
 
   // Wait for API call to complete
   await screen.findByRole('dialog');
-  expect(fetchMock.callHistory.called()).toBe(true);
-});
+  await waitFor(
+    () => {
+      expect(fetchMock.callHistory.called()).toBe(true);
+    },
+    { timeout: 15000 },
+  );
+}, 30000);
 
 test('discards changes when clicking Discard button in unsaved changes alert', async () => {
   const onHide = jest.fn();
@@ -483,12 +604,23 @@ test('creates new theme when saving', async () => {
 
   const nameInput = screen.getByPlaceholderText('Enter theme name');
   await userEvent.type(nameInput, 'New Theme');
+  await addValidJsonData();
 
-  const saveButton = await screen.findByRole('button', { name: 'Add' });
+  // Wait for validation to complete and button to become enabled
+  const saveButton = await waitFor(
+    () => {
+      const button = screen.getByRole('button', { name: 'Add' });
+      expect(button).toBeEnabled();
+      return button;
+    },
+    { timeout: 10000 },
+  );
   await userEvent.click(saveButton);
 
   expect(await screen.findByRole('dialog')).toBeInTheDocument();
-  expect(fetchMock.callHistory.called(postThemeMockName)).toBe(true);
+  await waitFor(() => {
+    expect(fetchMock.callHistory.called(postThemeMockName)).toBe(true);
+  });
 });
 
 test('updates existing theme when saving', async () => {
@@ -536,14 +668,24 @@ test('handles API errors gracefully', async () => {
 
   const nameInput = screen.getByPlaceholderText('Enter theme name');
   await userEvent.type(nameInput, 'New Theme');
+  await addValidJsonData();
 
-  const saveButton = await screen.findByRole('button', { name: 'Add' });
-  expect(saveButton).toBeEnabled();
+  // Wait for validation to complete and button to become enabled
+  const saveButton = await waitFor(
+    () => {
+      const button = screen.getByRole('button', { name: 'Add' });
+      expect(button).toBeEnabled();
+      return button;
+    },
+    { timeout: 10000 },
+  );
 
   await userEvent.click(saveButton);
 
   await screen.findByRole('dialog');
-  expect(fetchMock.callHistory.called()).toBe(true);
+  await waitFor(() => {
+    expect(fetchMock.callHistory.called()).toBe(true);
+  });
 });
 
 test('applies theme locally when clicking Apply button', async () => {
diff --git a/superset-frontend/src/features/themes/ThemeModal.tsx b/superset-frontend/src/features/themes/ThemeModal.tsx
index 534e1aa1425..335d346360a 100644
--- a/superset-frontend/src/features/themes/ThemeModal.tsx
+++ b/superset-frontend/src/features/themes/ThemeModal.tsx
@@ -43,10 +43,10 @@ import {
   Space,
   Tooltip,
 } from '@superset-ui/core/components';
-import { useJsonValidation } from '@superset-ui/core/components/AsyncAceEditor';
 import type { editors } from '@apache-superset/core';
 import { EditorHost } from 'src/core/editors';
 import { Typography } from '@superset-ui/core/components/Typography';
+import { useThemeValidation } from 'src/theme/hooks/useThemeValidation';
 import { OnlyKeyWithType } from 'src/utils/types';
 import { ThemeObject } from './types';
 
@@ -147,10 +147,9 @@ const ThemeModal: FunctionComponent<ThemeModalProps> = ({
     SupersetText?.THEME_MODAL?.DOCUMENTATION_URL ||
     'https://superset.apache.org/docs/configuration/theming/';
 
-  // JSON validation annotations using reusable hook
-  const jsonAnnotations = useJsonValidation(currentTheme?.json_data, {
-    enabled: !isReadOnly,
-    errorPrefix: 'Invalid JSON syntax',
+  // Theme validation (structure + token names)
+  const validation = useThemeValidation(currentTheme?.json_data || '', {
+    enabled: !isReadOnly && Boolean(currentTheme?.json_data),
   });
 
   // theme fetch logic
@@ -178,6 +177,15 @@ const ThemeModal: FunctionComponent<ThemeModalProps> = ({
   }, [onHide]);
 
   const onSave = useCallback(() => {
+    // Synchronous JSON guard to catch invalid JSON before API call
+    // This handles the race condition where debounced validation hasn't updated yet
+    try {
+      JSON.parse(currentTheme?.json_data || '');
+    } catch {
+      addDangerToast(t('Invalid JSON configuration'));
+      return;
+    }
+
     if (isEditMode) {
       // Edit
       if (currentTheme?.id) {
@@ -211,6 +219,7 @@ const ThemeModal: FunctionComponent<ThemeModalProps> = ({
     createResource,
     onThemeAdd,
     hide,
+    addDangerToast,
   ]);
 
   const handleCancel = useCallback(() => {
@@ -306,27 +315,22 @@ const ThemeModal: FunctionComponent<ThemeModalProps> = ({
     [currentTheme],
   );
 
-  const validate = useCallback(() => {
-    if (isReadOnly) {
+  const validate = () => {
+    if (isReadOnly || !currentTheme) {
       setDisableSave(true);
       return;
     }
 
-    if (
-      currentTheme?.theme_name.length &&
-      currentTheme?.json_data?.length &&
-      isValidJson(currentTheme.json_data)
-    ) {
-      setDisableSave(false);
-    } else {
-      setDisableSave(true);
-    }
-  }, [
-    currentTheme?.theme_name,
-    currentTheme?.json_data,
-    isReadOnly,
-    isValidJson,
-  ]);
+    const hasValidName = Boolean(currentTheme?.theme_name?.trim());
+    const hasValidJsonData = Boolean(currentTheme?.json_data?.trim());
+
+    // Block save only on ERRORS (not warnings)
+    // Errors: JSON syntax errors, empty themes
+    // Warnings: Unknown tokens, null values (non-blocking)
+    const canSave = hasValidName && hasValidJsonData && !validation.hasErrors;
+
+    setDisableSave(!canSave);
+  };
 
   // Initialize
   useEffect(() => {
@@ -360,7 +364,12 @@ const ThemeModal: FunctionComponent<ThemeModalProps> = ({
   // Validation
   useEffect(() => {
     validate();
-  }, [validate]);
+  }, [
+    currentTheme ? currentTheme.theme_name : '',
+    currentTheme ? currentTheme.json_data : '',
+    isReadOnly,
+    validation.hasErrors,
+  ]);
 
   // Show/hide
   useEffect(() => {
@@ -490,7 +499,10 @@ const ThemeModal: FunctionComponent<ThemeModalProps> = ({
                   >
                     {t('documentation')}
                   </a>
-                  {t(' for details.')}
+                  {t(' for details.')}{' '}
+                  <Typography.Text type="secondary">
+                    {t('Unknown tokens will be highlighted as warnings.')}
+                  </Typography.Text>
                 </span>
               }
             />
@@ -506,7 +518,7 @@ const ThemeModal: FunctionComponent<ThemeModalProps> = ({
                 lineNumbers
                 width="100%"
                 height="250px"
-                annotations={toEditorAnnotations(jsonAnnotations)}
+                annotations={toEditorAnnotations(validation.annotations)}
               />
             </StyledEditorWrapper>
             {canDevelopThemes && (
@@ -520,7 +532,8 @@ const ThemeModal: FunctionComponent<ThemeModalProps> = ({
                     onClick={onApply}
                     disabled={
                       !currentTheme?.json_data ||
-                      !isValidJson(currentTheme.json_data)
+                      !isValidJson(currentTheme.json_data) ||
+                      validation.hasErrors
                     }
                     buttonStyle="secondary"
                   >
diff --git a/superset-frontend/src/theme/ThemeController.ts b/superset-frontend/src/theme/ThemeController.ts
index ae798dfc97a..91f318279e0 100644
--- a/superset-frontend/src/theme/ThemeController.ts
+++ b/superset-frontend/src/theme/ThemeController.ts
@@ -143,8 +143,26 @@ export class ThemeController {
     // Setup change callback
     if (onChange) this.onChangeCallbacks.add(onChange);
 
-    // Apply initial theme and persist mode
-    this.applyTheme(initialTheme);
+    // Apply initial theme with recovery for corrupted stored themes
+    try {
+      this.applyTheme(initialTheme);
+    } catch (error) {
+      // Corrupted dev override or CRUD theme in storage - clear and retry with defaults
+      console.warn(
+        'Failed to apply stored theme, clearing invalid overrides:',
+        error,
+      );
+      this.devThemeOverride = null;
+      this.crudThemeId = null;
+      this.storage.removeItem(STORAGE_KEYS.DEV_THEME_OVERRIDE);
+      this.storage.removeItem(STORAGE_KEYS.CRUD_THEME_ID);
+      this.storage.removeItem(STORAGE_KEYS.APPLIED_THEME_ID);
+
+      // Retry with clean default theme
+      this.currentMode = ThemeMode.DEFAULT;
+      const safeTheme = this.defaultTheme || {};
+      this.applyTheme(safeTheme);
+    }
     this.persistMode();
   }
 
@@ -229,14 +247,8 @@ export class ThemeController {
         return this.dashboardThemes.get(themeId)!;
       }
 
-      // Fetch theme config from API using SupersetClient for proper auth
-      const getTheme = makeApi<void, { result: { json_data: string } }>({
-        method: 'GET',
-        endpoint: `/api/v1/theme/${themeId}`,
-      });
-
-      const { result } = await getTheme();
-      const themeConfig = JSON.parse(result.json_data);
+      // Use the enhanced fetchCrudTheme method which includes validation if feature flag is enabled
+      const themeConfig = await this.fetchCrudTheme(themeId);
 
       if (themeConfig) {
         // Controller creates and owns the dashboard theme
@@ -329,7 +341,6 @@ export class ThemeController {
 
     const theme: AnyThemeConfig | null = this.getThemeForMode(mode);
     if (!theme) {
-      console.warn(`Theme for mode ${mode} not found, falling back to default`);
       this.fallbackToDefaultMode();
       return;
     }
@@ -535,7 +546,7 @@ export class ThemeController {
    * Updates the theme.
    * @param theme - The new theme to apply
    */
-  private updateTheme(theme?: AnyThemeConfig): void {
+  private async updateTheme(theme?: AnyThemeConfig): Promise<void> {
     try {
       // If no config provided, use current mode to get theme
       if (!theme) {
@@ -551,18 +562,41 @@ export class ThemeController {
       this.persistMode();
       this.notifyListeners();
     } catch (error) {
-      console.error('Failed to update theme:', error);
-      this.fallbackToDefaultMode();
+      // Clear potentially corrupted overrides before fallback
+      // This mirrors the constructor's recovery logic to prevent
+      // repeated failures from a malformed devThemeOverride or crudThemeId
+      this.devThemeOverride = null;
+      this.crudThemeId = null;
+      this.storage.removeItem(STORAGE_KEYS.DEV_THEME_OVERRIDE);
+      this.storage.removeItem(STORAGE_KEYS.CRUD_THEME_ID);
+      this.storage.removeItem(STORAGE_KEYS.APPLIED_THEME_ID);
+
+      await this.fallbackToDefaultMode();
     }
   }
 
   /**
-   * Fallback to default mode with error recovery.
+   * Fallback to default mode with runtime error recovery.
+   * Tries to fetch a fresh system default theme from the API.
    */
-  private fallbackToDefaultMode(): void {
+  private async fallbackToDefaultMode(): Promise<void> {
     this.currentMode = ThemeMode.DEFAULT;
 
-    // Get the default theme which will have the correct algorithm
+    // Try to fetch fresh system default theme from server
+    const freshSystemTheme = await this.fetchSystemDefaultTheme();
+
+    if (freshSystemTheme) {
+      try {
+        await this.applyThemeWithRecovery(freshSystemTheme);
+        this.persistMode();
+        this.notifyListeners();
+        return;
+      } catch (error) {
+        // Fresh theme also failed, continue to final fallback
+      }
+    }
+
+    // Final fallback: use cached default theme or built-in theme
     const defaultTheme: AnyThemeConfig =
       this.getThemeForMode(ThemeMode.DEFAULT) || this.defaultTheme || {};
 
@@ -796,10 +830,25 @@ export class ThemeController {
       this.loadFonts(fontUrls);
     } catch (error) {
       console.error('Failed to apply theme:', error);
-      this.fallbackToDefaultMode();
+      // Re-throw the error so updateTheme can handle fallback logic
+      throw error;
     }
   }
 
+  private async applyThemeWithRecovery(theme: AnyThemeConfig): Promise<void> {
+    // Note: This method re-throws errors to the caller instead of calling
+    // fallbackToDefaultMode directly, to avoid infinite recursion since
+    // fallbackToDefaultMode calls this method. The caller's try/catch
+    // handles the fallback flow.
+    const normalizedConfig = normalizeThemeConfig(theme);
+    this.globalTheme.setConfig(normalizedConfig);
+
+    // Load custom fonts if specified, mirroring applyTheme() behavior
+    const fontUrls = (normalizedConfig?.token as Record<string, unknown>)
+      ?.fontUrls as string[] | undefined;
+    this.loadFonts(fontUrls);
+  }
+
   /**
    * Loads custom fonts from theme configuration.
    * Injects CSS @import statements for font URLs that haven't been loaded yet.
@@ -896,14 +945,17 @@ export class ThemeController {
   /**
    * Fetches a theme configuration from the CRUD API.
    * @param themeId - The ID of the theme to fetch
-   * @returns The theme configuration or null if not found
+   * @returns The theme configuration or null if fetch fails
    */
   private async fetchCrudTheme(
     themeId: string,
   ): Promise<AnyThemeConfig | null> {
     try {
       // Use SupersetClient for proper authentication handling
-      const getTheme = makeApi<void, { result: { json_data: string } }>({
+      const getTheme = makeApi<
+        void,
+        { result: { json_data: string; theme_name?: string } }
+      >({
         method: 'GET',
         endpoint: `/api/v1/theme/${themeId}`,
       });
@@ -911,10 +963,65 @@ export class ThemeController {
       const { result } = await getTheme();
       const themeConfig = JSON.parse(result.json_data);
 
+      if (!themeConfig || typeof themeConfig !== 'object') {
+        console.error(`Invalid theme configuration for theme ${themeId}`);
+        return null;
+      }
+
+      // Return theme as-is
+      // Invalid tokens will be handled by Ant Design at runtime
+      // Runtime errors will be caught by applyThemeWithRecovery()
       return themeConfig;
     } catch (error) {
       console.error('Failed to fetch CRUD theme:', error);
       return null;
     }
   }
+
+  /**
+   * Fetches a fresh system default theme from the API for runtime recovery.
+   * Tries multiple fallback strategies to find a valid theme.
+   *
+   * Note: Uses raw fetch() instead of SupersetClient because ThemeController
+   * initializes early in the app lifecycle, before SupersetClient is fully
+   * configured. This avoids boot-time circular dependencies.
+   *
+   * @returns The system default theme configuration or null if not found
+   */
+  private async fetchSystemDefaultTheme(): Promise<AnyThemeConfig | null> {
+    try {
+      // Try to fetch theme marked as system default (is_system_default=true)
+      const defaultResponse = await fetch(
+        '/api/v1/theme/?q=(filters:!((col:is_system_default,opr:eq,value:!t)))',
+      );
+      if (defaultResponse.ok) {
+        const data = await defaultResponse.json();
+        if (data.result?.length > 0) {
+          const themeConfig = JSON.parse(data.result[0].json_data);
+          if (themeConfig && typeof themeConfig === 'object') {
+            return themeConfig;
+          }
+        }
+      }
+
+      // Fallback: Try to fetch system theme named 'THEME_DEFAULT'
+      const fallbackResponse = await fetch(
+        '/api/v1/theme/?q=(filters:!((col:theme_name,opr:eq,value:THEME_DEFAULT),(col:is_system,opr:eq,value:!t)))',
+      );
+      if (fallbackResponse.ok) {
+        const fallbackData = await fallbackResponse.json();
+        if (fallbackData.result?.length > 0) {
+          const themeConfig = JSON.parse(fallbackData.result[0].json_data);
+          if (themeConfig && typeof themeConfig === 'object') {
+            return themeConfig;
+          }
+        }
+      }
+    } catch (error) {
+      // Log for debugging but don't fail - fallback to cached theme will be used
+      console.warn('Failed to fetch system default theme:', error);
+    }
+
+    return null;
+  }
 }
diff --git a/superset-frontend/src/theme/hooks/useThemeValidation.test.ts b/superset-frontend/src/theme/hooks/useThemeValidation.test.ts
new file mode 100644
index 00000000000..a0bf70539b1
--- /dev/null
+++ b/superset-frontend/src/theme/hooks/useThemeValidation.test.ts
@@ -0,0 +1,133 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+import { renderHook } from '@testing-library/react-hooks';
+import { useThemeValidation } from './useThemeValidation';
+
+test('useThemeValidation validates valid theme with standard tokens', () => {
+  const validTheme = JSON.stringify({
+    token: {
+      colorPrimary: '#1890ff',
+      fontSize: 14,
+    },
+  });
+
+  const { result } = renderHook(() => useThemeValidation(validTheme));
+
+  expect(result.current.hasErrors).toBe(false);
+  expect(result.current.hasWarnings).toBe(false);
+  expect(result.current.annotations).toHaveLength(0);
+});
+
+test('useThemeValidation shows warnings for unknown tokens', () => {
+  const themeWithUnknownToken = JSON.stringify({
+    token: {
+      colorPrimary: '#1890ff',
+      unknownToken: 'value',
+    },
+  });
+
+  const { result } = renderHook(() =>
+    useThemeValidation(themeWithUnknownToken),
+  );
+
+  expect(result.current.hasErrors).toBe(false);
+  expect(result.current.hasWarnings).toBe(true);
+  expect(result.current.annotations.length).toBeGreaterThan(0);
+  expect(result.current.annotations[0].type).toBe('warning');
+});
+
+test('useThemeValidation shows error for empty theme', () => {
+  const emptyTheme = JSON.stringify({});
+
+  const { result } = renderHook(() => useThemeValidation(emptyTheme));
+
+  expect(result.current.hasErrors).toBe(true);
+  expect(result.current.annotations.length).toBeGreaterThan(0);
+  expect(result.current.annotations[0].type).toBe('error');
+  expect(result.current.annotations[0].text).toContain('cannot be empty');
+});
+
+test('useThemeValidation shows error for invalid JSON syntax', () => {
+  const invalidJson = '{invalid json}';
+
+  const { result } = renderHook(() => useThemeValidation(invalidJson));
+
+  expect(result.current.hasErrors).toBe(true);
+  expect(result.current.annotations.length).toBeGreaterThan(0);
+  expect(result.current.annotations[0].type).toBe('error');
+});
+
+test('useThemeValidation skips validation for empty string', () => {
+  const { result } = renderHook(() => useThemeValidation(''));
+
+  expect(result.current.hasErrors).toBe(false);
+  expect(result.current.hasWarnings).toBe(false);
+  expect(result.current.annotations).toHaveLength(0);
+});
+
+test('useThemeValidation validates Superset custom tokens', () => {
+  const themeWithCustomToken = JSON.stringify({
+    token: {
+      brandLogoUrl: '/static/logo.png',
+      brandSpinnerSvg: '<svg></svg>',
+    },
+  });
+
+  const { result } = renderHook(() => useThemeValidation(themeWithCustomToken));
+
+  expect(result.current.hasErrors).toBe(false);
+  expect(result.current.hasWarnings).toBe(false);
+  expect(result.current.annotations).toHaveLength(0);
+});
+
+test('useThemeValidation allows theme with only algorithm', () => {
+  const themeWithAlgorithm = JSON.stringify({
+    algorithm: 'dark',
+  });
+
+  const { result } = renderHook(() => useThemeValidation(themeWithAlgorithm));
+
+  expect(result.current.hasErrors).toBe(false);
+  expect(result.current.annotations).toHaveLength(0);
+});
+
+test('useThemeValidation shows warning for null token value', () => {
+  const themeWithNullValue = JSON.stringify({
+    token: {
+      colorPrimary: null,
+    },
+  });
+
+  const { result } = renderHook(() => useThemeValidation(themeWithNullValue));
+
+  expect(result.current.hasErrors).toBe(false);
+  expect(result.current.hasWarnings).toBe(true);
+  expect(result.current.annotations[0].type).toBe('warning');
+  expect(result.current.annotations[0].text).toContain('null/undefined');
+});
+
+test('useThemeValidation respects enabled option', () => {
+  const invalidJson = '{invalid}';
+
+  const { result } = renderHook(() =>
+    useThemeValidation(invalidJson, { enabled: false }),
+  );
+
+  expect(result.current.annotations).toHaveLength(0);
+});
diff --git a/superset-frontend/src/theme/hooks/useThemeValidation.ts b/superset-frontend/src/theme/hooks/useThemeValidation.ts
new file mode 100644
index 00000000000..4b8b5bd0b61
--- /dev/null
+++ b/superset-frontend/src/theme/hooks/useThemeValidation.ts
@@ -0,0 +1,155 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+import { useMemo, useState, useEffect } from 'react';
+import { useJsonValidation } from '@superset-ui/core/components/AsyncAceEditor';
+import type { JsonValidationAnnotation } from '@superset-ui/core/components/AsyncAceEditor';
+import type { AnyThemeConfig } from '@apache-superset/core/ui';
+import { validateTheme } from '../utils/themeStructureValidation';
+
+/**
+ * Find the line number where a specific token appears in JSON string.
+ * Uses improved logic to handle nested objects and avoid false positives.
+ */
+function findTokenLineInJson(jsonString: string, tokenName: string): number {
+  if (!jsonString || !tokenName) {
+    return 0;
+  }
+
+  // Handle special _root token for structural errors
+  if (tokenName === '_root') {
+    return 0;
+  }
+
+  const lines = jsonString.split('\n');
+
+  // Look for the token name as a JSON property key
+  // Pattern: "tokenName" followed by : (with possible whitespace)
+  const propertyPattern = new RegExp(
+    `"${tokenName.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')}"\\s*:`,
+  );
+
+  for (let i = 0; i < lines.length; i += 1) {
+    if (propertyPattern.test(lines[i].trim())) {
+      return i; // Return 0-based line number for AceEditor
+    }
+  }
+
+  // Fallback: simple string search for edge cases
+  const searchPattern = `"${tokenName}"`;
+  for (let i = 0; i < lines.length; i += 1) {
+    if (lines[i].includes(searchPattern)) {
+      return i;
+    }
+  }
+
+  // If token not found, return line 0
+  return 0;
+}
+
+export interface ThemeValidationResult {
+  annotations: JsonValidationAnnotation[];
+  hasErrors: boolean; // true if errors exist (blocks save)
+  hasWarnings: boolean; // true if warnings exist (non-blocking)
+}
+
+export interface UseThemeValidationOptions {
+  /** Whether to enable validation. Default: true */
+  enabled?: boolean;
+  /** Debounce delay in milliseconds for validation. Default: 300 */
+  debounceMs?: number;
+}
+
+/**
+ * Theme validation hook with live feedback.
+ * - Errors (JSON syntax, empty theme) block save/apply
+ * - Warnings (unknown tokens, null values) allow save/apply
+ *
+ * This hook validates structure and token names only.
+ * Token values are validated by Ant Design at runtime.
+ */
+export function useThemeValidation(
+  jsonValue?: string,
+  options: UseThemeValidationOptions = {},
+): ThemeValidationResult {
+  const { enabled = true, debounceMs = 300 } = options;
+
+  const [debouncedValue, setDebouncedValue] = useState(jsonValue);
+
+  // Debounce for performance
+  useEffect(() => {
+    const timer = setTimeout(() => setDebouncedValue(jsonValue), debounceMs);
+    return () => clearTimeout(timer);
+  }, [jsonValue, debounceMs]);
+
+  // JSON syntax validation (ERRORS)
+  const jsonAnnotations = useJsonValidation(debouncedValue, {
+    enabled,
+    errorPrefix: 'Invalid JSON',
+  });
+
+  // Theme structure validation (ERRORS + WARNINGS)
+  const themeAnnotations = useMemo(() => {
+    // Skip if disabled or JSON is invalid
+    if (!enabled || jsonAnnotations.length > 0 || !debouncedValue?.trim()) {
+      return [];
+    }
+
+    try {
+      const config: AnyThemeConfig = JSON.parse(debouncedValue);
+      const result = validateTheme(config);
+
+      const annotations: JsonValidationAnnotation[] = [];
+
+      // Convert errors to annotations (blocks save)
+      result.errors.forEach(issue => {
+        annotations.push({
+          type: 'error',
+          row: findTokenLineInJson(debouncedValue, issue.tokenName),
+          column: 0,
+          text: issue.message,
+        });
+      });
+
+      // Convert warnings to annotations (non-blocking)
+      result.warnings.forEach(issue => {
+        annotations.push({
+          type: 'warning',
+          row: findTokenLineInJson(debouncedValue, issue.tokenName),
+          column: 0,
+          text: issue.message,
+        });
+      });
+
+      return annotations;
+    } catch {
+      // JSON parsing error already caught by jsonAnnotations
+      return [];
+    }
+  }, [enabled, debouncedValue, jsonAnnotations]);
+
+  return useMemo(() => {
+    const allAnnotations = [...jsonAnnotations, ...themeAnnotations];
+
+    return {
+      annotations: allAnnotations,
+      hasErrors: allAnnotations.some(a => a.type === 'error'),
+      hasWarnings: allAnnotations.some(a => a.type === 'warning'),
+    };
+  }, [jsonAnnotations, themeAnnotations]);
+}
diff --git a/superset-frontend/src/theme/tests/ThemeController.test.ts b/superset-frontend/src/theme/tests/ThemeController.test.ts
index f92d76fe439..278d85f8c26 100644
--- a/superset-frontend/src/theme/tests/ThemeController.test.ts
+++ b/superset-frontend/src/theme/tests/ThemeController.test.ts
@@ -833,6 +833,202 @@ test('ThemeController handles theme application errors', () => {
   fallbackSpy.mockRestore();
 });
 
+test('ThemeController constructor recovers from corrupted stored theme', () => {
+  // Simulate corrupted dev theme override in storage
+  const corruptedTheme = { token: { colorPrimary: '#ff0000' } };
+  mockLocalStorage.getItem.mockImplementation((key: string) => {
+    if (key === 'superset-dev-theme-override') {
+      return JSON.stringify(corruptedTheme);
+    }
+    return null;
+  });
+
+  // Mock Theme.fromConfig to return object with toSerializedConfig
+  mockThemeFromConfig.mockReturnValue({
+    ...mockThemeObject,
+    toSerializedConfig: () => corruptedTheme,
+  });
+
+  // First call throws (corrupted theme), second call succeeds (fallback)
+  let callCount = 0;
+  mockSetConfig.mockImplementation(() => {
+    callCount += 1;
+    if (callCount === 1) {
+      throw new Error('Invalid theme configuration');
+    }
+  });
+
+  // Should not throw - constructor should recover
+  const controller = createController();
+
+  // Verify recovery happened - use shared consoleSpy to avoid interfering with other tests
+  expect(consoleSpy).toHaveBeenCalledWith(
+    'Failed to apply stored theme, clearing invalid overrides:',
+    expect.any(Error),
+  );
+
+  // Verify invalid overrides were cleared from storage
+  expect(mockLocalStorage.removeItem).toHaveBeenCalledWith(
+    'superset-dev-theme-override',
+  );
+  expect(mockLocalStorage.removeItem).toHaveBeenCalledWith(
+    'superset-crud-theme-id',
+  );
+  expect(mockLocalStorage.removeItem).toHaveBeenCalledWith(
+    'superset-applied-theme-id',
+  );
+
+  // Verify controller is in a valid state
+  expect(controller.getCurrentMode()).toBe(ThemeMode.DEFAULT);
+});
+
+test('recovery flow: fetchSystemDefaultTheme returns theme → applies fetched theme', async () => {
+  // Test: fallbackToDefaultMode fetches theme from API and applies it
+  // Flow: fallbackToDefaultMode → fetchSystemDefaultTheme → applyThemeWithRecovery
+
+  const originalFetch = global.fetch;
+  const controller = createController();
+
+  try {
+    // Mock fetch to return a system default theme from API
+    const systemTheme = { token: { colorPrimary: '#recovery-theme' } };
+    const mockFetch = jest.fn().mockResolvedValueOnce({
+      ok: true,
+      json: async () => ({
+        result: [{ json_data: JSON.stringify(systemTheme) }],
+      }),
+    });
+    global.fetch = mockFetch;
+
+    // Track setConfig calls to verify the fetched theme is applied
+    const setConfigCalls: unknown[] = [];
+    mockSetConfig.mockImplementation((config: unknown) => {
+      setConfigCalls.push(config);
+    });
+
+    // Trigger fallbackToDefaultMode (simulates what happens after applyTheme fails)
+    await (controller as any).fallbackToDefaultMode();
+
+    // Verify API was called to fetch system default theme
+    expect(mockFetch).toHaveBeenCalledWith(
+      expect.stringContaining('/api/v1/theme/'),
+    );
+
+    // Verify the fetched theme was applied via applyThemeWithRecovery
+    expect(setConfigCalls.length).toBe(1);
+    expect(setConfigCalls[0]).toEqual(
+      expect.objectContaining({
+        token: expect.objectContaining({ colorPrimary: '#recovery-theme' }),
+      }),
+    );
+
+    // Verify controller is in default mode
+    expect(controller.getCurrentMode()).toBe(ThemeMode.DEFAULT);
+  } finally {
+    global.fetch = originalFetch;
+  }
+});
+
+test('recovery flow: both API fetches fail → falls back to cached default theme', async () => {
+  // Test: When fetchSystemDefaultTheme fails, fallbackToDefaultMode uses cached theme
+  // Flow: fallbackToDefaultMode → fetchSystemDefaultTheme (fails) → applyTheme(cached)
+
+  const originalFetch = global.fetch;
+  const controller = createController();
+
+  try {
+    // Mock fetch to fail for both API endpoints
+    const mockFetch = jest.fn().mockRejectedValue(new Error('Network error'));
+    global.fetch = mockFetch;
+
+    // Track setConfig calls
+    const setConfigCalls: unknown[] = [];
+    mockSetConfig.mockImplementation((config: unknown) => {
+      setConfigCalls.push(config);
+    });
+
+    // Trigger fallbackToDefaultMode
+    await (controller as any).fallbackToDefaultMode();
+
+    // Verify fetch was attempted
+    expect(mockFetch).toHaveBeenCalled();
+
+    // Verify fallback to cached default theme was applied via applyTheme
+    expect(setConfigCalls.length).toBe(1);
+    expect(setConfigCalls[0]).toEqual(
+      expect.objectContaining({
+        token: expect.objectContaining({
+          colorBgBase: '#ededed', // From DEFAULT_THEME in test setup
+        }),
+      }),
+    );
+
+    // Verify controller is in default mode
+    expect(controller.getCurrentMode()).toBe(ThemeMode.DEFAULT);
+  } finally {
+    global.fetch = originalFetch;
+  }
+});
+
+test('recovery flow: fetched theme fails to apply → falls back to cached default', async () => {
+  // Test: When applyThemeWithRecovery fails, fallbackToDefaultMode uses cached theme
+  // Flow: fallbackToDefaultMode → fetchSystemDefaultTheme → applyThemeWithRecovery (fails) → applyTheme(cached)
+
+  const originalFetch = global.fetch;
+  const controller = createController();
+
+  try {
+    // Mock fetch to return a theme
+    const systemTheme = { token: { colorPrimary: '#bad-theme' } };
+    const mockFetch = jest.fn().mockResolvedValueOnce({
+      ok: true,
+      json: async () => ({
+        result: [{ json_data: JSON.stringify(systemTheme) }],
+      }),
+    });
+    global.fetch = mockFetch;
+
+    // First setConfig call (applyThemeWithRecovery) fails, second (applyTheme) succeeds
+    const setConfigCalls: unknown[] = [];
+    mockSetConfig.mockImplementation((config: unknown) => {
+      setConfigCalls.push(config);
+      if (setConfigCalls.length === 1) {
+        throw new Error('Fetched theme failed to apply');
+      }
+    });
+
+    // Trigger fallbackToDefaultMode
+    await (controller as any).fallbackToDefaultMode();
+
+    // Verify fetch was called
+    expect(mockFetch).toHaveBeenCalled();
+
+    // Verify both attempts were made: fetched theme (failed) then cached default
+    expect(setConfigCalls.length).toBe(2);
+
+    // First call was the fetched theme (which failed)
+    expect(setConfigCalls[0]).toEqual(
+      expect.objectContaining({
+        token: expect.objectContaining({ colorPrimary: '#bad-theme' }),
+      }),
+    );
+
+    // Second call was the cached default theme
+    expect(setConfigCalls[1]).toEqual(
+      expect.objectContaining({
+        token: expect.objectContaining({
+          colorBgBase: '#ededed', // From DEFAULT_THEME
+        }),
+      }),
+    );
+
+    // Verify controller is in default mode
+    expect(controller.getCurrentMode()).toBe(ThemeMode.DEFAULT);
+  } finally {
+    global.fetch = originalFetch;
+  }
+});
+
 // Cleanup tests
 test('ThemeController cleans up listeners on destroy', () => {
   const mockMediaQueryInstance = {
diff --git a/superset-frontend/src/theme/utils/antdTokenNames.test.ts b/superset-frontend/src/theme/utils/antdTokenNames.test.ts
new file mode 100644
index 00000000000..4726dfc9b30
--- /dev/null
+++ b/superset-frontend/src/theme/utils/antdTokenNames.test.ts
@@ -0,0 +1,108 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+import {
+  isValidTokenName,
+  isSupersetCustomToken,
+  getAllValidTokenNames,
+} from './antdTokenNames';
+
+test('isValidTokenName recognizes standard Ant Design tokens', () => {
+  expect(isValidTokenName('colorPrimary')).toBe(true);
+  expect(isValidTokenName('fontSize')).toBe(true);
+  expect(isValidTokenName('padding')).toBe(true);
+  expect(isValidTokenName('borderRadius')).toBe(true);
+});
+
+test('isValidTokenName recognizes Superset custom tokens', () => {
+  expect(isValidTokenName('brandLogoUrl')).toBe(true);
+  expect(isValidTokenName('brandSpinnerSvg')).toBe(true);
+  expect(isValidTokenName('fontSizeXS')).toBe(true);
+  expect(isValidTokenName('echartsOptionsOverrides')).toBe(true);
+});
+
+test('isValidTokenName rejects unknown tokens', () => {
+  expect(isValidTokenName('fooBarBaz')).toBe(false);
+  expect(isValidTokenName('colrPrimary')).toBe(false);
+  expect(isValidTokenName('invalidToken')).toBe(false);
+});
+
+test('isValidTokenName handles edge cases', () => {
+  expect(isValidTokenName('')).toBe(false);
+  expect(isValidTokenName('  ')).toBe(false);
+});
+
+test('isSupersetCustomToken identifies Superset-specific tokens', () => {
+  expect(isSupersetCustomToken('brandLogoUrl')).toBe(true);
+  expect(isSupersetCustomToken('brandSpinnerSvg')).toBe(true);
+  expect(isSupersetCustomToken('fontSizeXS')).toBe(true);
+  expect(isSupersetCustomToken('fontUrls')).toBe(true);
+});
+
+test('isSupersetCustomToken returns false for Ant Design tokens', () => {
+  expect(isSupersetCustomToken('colorPrimary')).toBe(false);
+  expect(isSupersetCustomToken('fontSize')).toBe(false);
+});
+
+test('isSupersetCustomToken returns false for unknown tokens', () => {
+  expect(isSupersetCustomToken('fooBar')).toBe(false);
+});
+
+test('getAllValidTokenNames returns categorized token names', () => {
+  const result = getAllValidTokenNames();
+
+  expect(result).toHaveProperty('antdTokens');
+  expect(result).toHaveProperty('supersetTokens');
+  expect(result).toHaveProperty('total');
+});
+
+test('getAllValidTokenNames has reasonable token counts', () => {
+  const result = getAllValidTokenNames();
+
+  // Ant Design tokens should exist (avoid brittle exact count that breaks on upgrades)
+  expect(result.antdTokens.length).toBeGreaterThan(0);
+  expect(result.antdTokens).toContain('colorPrimary');
+  expect(result.antdTokens).toContain('fontSize');
+  expect(result.antdTokens).toContain('borderRadius');
+
+  // Superset custom tokens should exist
+  expect(result.supersetTokens.length).toBeGreaterThan(0);
+  expect(result.supersetTokens).toContain('brandLogoUrl');
+  expect(result.supersetTokens).toContain('fontUrls');
+
+  // Total should be sum of both
+  expect(result.total).toBe(
+    result.antdTokens.length + result.supersetTokens.length,
+  );
+});
+
+test('getAllValidTokenNames includes known Superset tokens', () => {
+  const result = getAllValidTokenNames();
+
+  expect(result.supersetTokens).toContain('brandLogoUrl');
+  expect(result.supersetTokens).toContain('brandSpinnerSvg');
+  expect(result.supersetTokens).toContain('fontSizeXS');
+});
+
+test('getAllValidTokenNames includes known Ant Design tokens', () => {
+  const result = getAllValidTokenNames();
+
+  expect(result.antdTokens).toContain('colorPrimary');
+  expect(result.antdTokens).toContain('fontSize');
+  expect(result.antdTokens).toContain('padding');
+});
diff --git a/superset-frontend/src/theme/utils/antdTokenNames.ts b/superset-frontend/src/theme/utils/antdTokenNames.ts
new file mode 100644
index 00000000000..567296c248a
--- /dev/null
+++ b/superset-frontend/src/theme/utils/antdTokenNames.ts
@@ -0,0 +1,115 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+import { theme } from 'antd';
+
+/**
+ * Superset-specific custom tokens that extend Ant Design's token system.
+ * These keys are derived from the SupersetSpecificTokens interface to ensure consistency.
+ */
+const SUPERSET_CUSTOM_TOKENS: Set<string> = new Set([
+  // Font extensions (fontWeightStrong is an Ant Design token, not Superset-specific)
+  'fontSizeXS',
+  'fontSizeXXL',
+  'fontWeightNormal',
+  'fontWeightLight',
+
+  // Brand tokens
+  'brandIconMaxWidth',
+  'brandLogoAlt',
+  'brandLogoUrl',
+  'brandLogoMargin',
+  'brandLogoHref',
+  'brandLogoHeight',
+
+  // Spinner tokens
+  'brandSpinnerUrl',
+  'brandSpinnerSvg',
+
+  // ECharts tokens
+  'echartsOptionsOverrides',
+  'echartsOptionsOverridesByChartType',
+
+  // Font loading
+  'fontUrls',
+]);
+
+/**
+ * Lazy-loaded cache of valid token names.
+ * Combines Ant Design tokens (extracted at runtime) + Superset custom tokens.
+ */
+let validTokenNamesCache: Set<string> | undefined;
+
+/**
+ * Get all valid token names (Ant Design + Superset custom).
+ * Uses lazy loading and caching for performance.
+ */
+function getValidTokenNames(): Set<string> {
+  if (validTokenNamesCache === undefined) {
+    // Extract all token names from Ant Design's default theme
+    const antdTokens = theme.getDesignToken();
+    const antdTokenNames = Object.keys(antdTokens);
+
+    // Combine with Superset custom tokens
+    validTokenNamesCache = new Set([
+      ...antdTokenNames,
+      ...SUPERSET_CUSTOM_TOKENS,
+    ]);
+  }
+  return validTokenNamesCache;
+}
+
+/**
+ * Check if a token name is valid (recognized by Ant Design OR Superset).
+ * @param tokenName - The token name to validate
+ * @returns true if the token is recognized, false otherwise
+ */
+export function isValidTokenName(tokenName: string): boolean {
+  return getValidTokenNames().has(tokenName);
+}
+
+/**
+ * Check if a token is a Superset custom token (not from Ant Design).
+ * @param tokenName - The token name to check
+ * @returns true if it's a Superset-specific token
+ */
+export function isSupersetCustomToken(tokenName: string): boolean {
+  return SUPERSET_CUSTOM_TOKENS.has(tokenName);
+}
+
+/**
+ * Get all valid token names, categorized by source.
+ * Useful for debugging and testing.
+ */
+export function getAllValidTokenNames(): {
+  antdTokens: string[];
+  supersetTokens: string[];
+  total: number;
+} {
+  const allTokens = getValidTokenNames();
+  const antdTokens = Array.from(allTokens).filter(
+    t => !isSupersetCustomToken(t),
+  );
+  const supersetTokens: string[] = Array.from(SUPERSET_CUSTOM_TOKENS);
+
+  return {
+    antdTokens,
+    supersetTokens,
+    total: allTokens.size,
+  };
+}
diff --git a/superset-frontend/src/theme/utils/themeStructureValidation.test.ts b/superset-frontend/src/theme/utils/themeStructureValidation.test.ts
new file mode 100644
index 00000000000..80e4edf32b4
--- /dev/null
+++ b/superset-frontend/src/theme/utils/themeStructureValidation.test.ts
@@ -0,0 +1,346 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+import type { AnyThemeConfig } from '@apache-superset/core/ui';
+import { validateTheme } from './themeStructureValidation';
+
+test('validateTheme validates a valid theme with standard tokens', () => {
+  const theme: AnyThemeConfig = {
+    token: {
+      colorPrimary: '#1890ff',
+      fontSize: 14,
+    },
+  };
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(true);
+  expect(result.errors).toHaveLength(0);
+  expect(result.warnings).toHaveLength(0);
+});
+
+test('validateTheme validates a theme with Superset custom tokens', () => {
+  const theme: AnyThemeConfig = {
+    token: {
+      colorPrimary: '#1890ff',
+      brandLogoUrl: '/static/logo.png',
+      brandSpinnerSvg: '<svg></svg>',
+    },
+  };
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(true);
+  expect(result.errors).toHaveLength(0);
+  expect(result.warnings).toHaveLength(0);
+});
+
+test('validateTheme warns about unknown token names', () => {
+  const theme: AnyThemeConfig = {
+    token: {
+      colorPrimary: '#1890ff',
+      fooBarBaz: 'invalid',
+      colrPrimary: '#ff0000', // Typo
+    },
+  };
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(true); // Warnings don't block
+  expect(result.errors).toHaveLength(0);
+  expect(result.warnings).toHaveLength(2);
+  expect(result.warnings[0].tokenName).toBe('fooBarBaz');
+  expect(result.warnings[1].tokenName).toBe('colrPrimary');
+  expect(result.warnings[0].severity).toBe('warning');
+});
+
+test('validateTheme warns about null/undefined token values', () => {
+  const theme: AnyThemeConfig = {
+    token: {
+      colorPrimary: null,
+      fontSize: undefined,
+    },
+  };
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(true);
+  expect(result.warnings).toHaveLength(2);
+  expect(result.warnings[0].message).toContain('null/undefined');
+  expect(result.warnings[1].message).toContain('null/undefined');
+});
+
+test('validateTheme errors on empty theme object', () => {
+  const theme: AnyThemeConfig = {};
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].tokenName).toBe('_root');
+  expect(result.errors[0].message).toContain('cannot be empty');
+});
+
+test('validateTheme errors on null theme config', () => {
+  const result = validateTheme(null as any);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].message).toContain('must be a valid object');
+});
+
+test('validateTheme allows theme with only algorithm', () => {
+  const theme: AnyThemeConfig = {
+    algorithm: 'dark' as any,
+  };
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(true);
+  expect(result.errors).toHaveLength(0);
+});
+
+test('validateTheme allows theme with only components', () => {
+  const theme: AnyThemeConfig = {
+    components: {
+      Button: {
+        colorPrimary: '#1890ff',
+      },
+    },
+  };
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(true);
+  expect(result.errors).toHaveLength(0);
+});
+
+test('validateTheme errors on theme with empty token object but no algorithm or components', () => {
+  const theme: AnyThemeConfig = {
+    token: {},
+  };
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].message).toContain('cannot be empty');
+});
+
+test('validateTheme combines errors and warnings correctly', () => {
+  const theme: AnyThemeConfig = {
+    token: {
+      colorPrimary: '#1890ff',
+      unknownToken: 'value',
+      nullToken: null,
+    },
+  };
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(true); // No errors, just warnings
+  expect(result.errors).toHaveLength(0);
+  expect(result.warnings.length).toBeGreaterThan(0);
+});
+
+test('validateTheme errors when token is an array instead of object', () => {
+  const theme = {
+    token: ['colorPrimary', '#1890ff'],
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].tokenName).toBe('_root');
+  expect(result.errors[0].message).toContain('must be an object');
+});
+
+test('validateTheme errors when token is a string instead of object', () => {
+  const theme = {
+    token: 'colorPrimary',
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].message).toContain('must be an object');
+});
+
+test('validateTheme errors when components is an array instead of object', () => {
+  const theme = {
+    token: { colorPrimary: '#1890ff' },
+    components: ['Button', 'Input'],
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].tokenName).toBe('_root');
+  expect(result.errors[0].message).toContain('Components configuration');
+  expect(result.errors[0].message).toContain('must be an object');
+});
+
+test('validateTheme errors when components is a primitive', () => {
+  const theme = {
+    token: { colorPrimary: '#1890ff' },
+    components: 'Button',
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].message).toContain('Components configuration');
+});
+
+test('validateTheme errors when algorithm is a number', () => {
+  const theme = {
+    token: { colorPrimary: '#1890ff' },
+    algorithm: 123,
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].tokenName).toBe('_root');
+  expect(result.errors[0].message).toContain('Algorithm must be a string');
+});
+
+test('validateTheme errors when algorithm is an object', () => {
+  const theme = {
+    token: { colorPrimary: '#1890ff' },
+    algorithm: { type: 'dark' },
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].message).toContain('Algorithm must be a string');
+});
+
+test('validateTheme allows algorithm as array of strings', () => {
+  const theme = {
+    algorithm: ['dark', 'compact'],
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(true);
+  expect(result.errors).toHaveLength(0);
+});
+
+test('validateTheme errors when algorithm array contains non-strings', () => {
+  const theme = {
+    token: { colorPrimary: '#1890ff' },
+    algorithm: ['dark', 123, 'compact'],
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].message).toContain('Algorithm must be a string');
+});
+
+test('validateTheme errors when token is explicitly null', () => {
+  const theme = {
+    token: null,
+    algorithm: 'dark',
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].tokenName).toBe('_root');
+  expect(result.errors[0].message).toContain('must be an object');
+  expect(result.errors[0].message).toContain('not null');
+});
+
+test('validateTheme errors when components is explicitly null', () => {
+  const theme = {
+    token: { colorPrimary: '#1890ff' },
+    components: null,
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].tokenName).toBe('_root');
+  expect(result.errors[0].message).toContain('Components configuration');
+  expect(result.errors[0].message).toContain('not null');
+});
+
+test('validateTheme errors when algorithm is explicitly null', () => {
+  const theme = {
+    token: { colorPrimary: '#1890ff' },
+    algorithm: null,
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].tokenName).toBe('_root');
+  expect(result.errors[0].message).toContain('Algorithm cannot be null');
+});
+
+test('validateTheme errors when algorithm string is not a valid value', () => {
+  const theme = {
+    algorithm: 'invalid-algorithm',
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].tokenName).toBe('_root');
+  expect(result.errors[0].message).toContain('Invalid algorithm value');
+  expect(result.errors[0].message).toContain('invalid-algorithm');
+  expect(result.errors[0].message).toContain('default, dark, system, compact');
+});
+
+test('validateTheme errors when algorithm array contains invalid values', () => {
+  const theme = {
+    algorithm: ['dark', 'invalid-mode', 'compact'],
+  } as unknown as AnyThemeConfig;
+
+  const result = validateTheme(theme);
+
+  expect(result.valid).toBe(false);
+  expect(result.errors).toHaveLength(1);
+  expect(result.errors[0].message).toContain('Invalid algorithm value');
+  expect(result.errors[0].message).toContain('invalid-mode');
+});
+
+test('validateTheme allows all valid algorithm values', () => {
+  const validAlgorithms = ['default', 'dark', 'system', 'compact'];
+
+  validAlgorithms.forEach(algo => {
+    const theme = { algorithm: algo } as unknown as AnyThemeConfig;
+    const result = validateTheme(theme);
+    expect(result.valid).toBe(true);
+    expect(result.errors).toHaveLength(0);
+  });
+});
diff --git a/superset-frontend/src/theme/utils/themeStructureValidation.ts b/superset-frontend/src/theme/utils/themeStructureValidation.ts
new file mode 100644
index 00000000000..affb884609d
--- /dev/null
+++ b/superset-frontend/src/theme/utils/themeStructureValidation.ts
@@ -0,0 +1,191 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+import type { AnyThemeConfig } from '@apache-superset/core/ui';
+import { isValidTokenName } from './antdTokenNames';
+
+/**
+ * Valid algorithm values that match backend ThemeMode enum.
+ * These correspond to Ant Design's built-in theme algorithms.
+ */
+const VALID_ALGORITHM_VALUES = new Set([
+  'default',
+  'dark',
+  'system',
+  'compact',
+]);
+
+export interface ValidationIssue {
+  tokenName: string;
+  severity: 'error' | 'warning';
+  message: string;
+}
+
+export interface ValidationResult {
+  valid: boolean; // false if ANY errors exist (warnings don't affect this)
+  errors: ValidationIssue[];
+  warnings: ValidationIssue[];
+}
+
+/**
+ * Validates theme structure and token names.
+ * - ERRORS block save/apply (invalid structure, empty themes)
+ * - WARNINGS allow save/apply but show in editor (unknown tokens, null values)
+ *
+ * This validation does NOT check token values - Ant Design handles that at runtime.
+ */
+export function validateTheme(themeConfig: AnyThemeConfig): ValidationResult {
+  const errors: ValidationIssue[] = [];
+  const warnings: ValidationIssue[] = [];
+
+  // ERROR: Null/invalid config
+  if (!themeConfig || typeof themeConfig !== 'object') {
+    errors.push({
+      tokenName: '_root',
+      severity: 'error',
+      message: 'Theme configuration must be a valid object',
+    });
+    return { valid: false, errors, warnings };
+  }
+
+  // ERROR: Empty theme (no tokens, no algorithm, no components)
+  const hasTokens =
+    themeConfig.token && Object.keys(themeConfig.token).length > 0;
+  const hasAlgorithm = Boolean(themeConfig.algorithm);
+  const hasComponents =
+    themeConfig.components && Object.keys(themeConfig.components).length > 0;
+
+  if (!hasTokens && !hasAlgorithm && !hasComponents) {
+    errors.push({
+      tokenName: '_root',
+      severity: 'error',
+      message:
+        'Theme cannot be empty. Add at least one token, algorithm, or component override.',
+    });
+    return { valid: false, errors, warnings };
+  }
+
+  // ERROR: token must be an object if present (null is also rejected by backend)
+  const rawToken = themeConfig.token;
+  if (rawToken !== undefined) {
+    if (
+      rawToken === null ||
+      typeof rawToken !== 'object' ||
+      Array.isArray(rawToken)
+    ) {
+      errors.push({
+        tokenName: '_root',
+        severity: 'error',
+        message:
+          'Token configuration must be an object, not null, array, or primitive',
+      });
+      return { valid: false, errors, warnings };
+    }
+  }
+  const tokens = rawToken ?? {};
+
+  // ERROR: components must be an object if present (null is also rejected by backend)
+  const rawComponents = themeConfig.components;
+  if (rawComponents !== undefined) {
+    if (
+      rawComponents === null ||
+      typeof rawComponents !== 'object' ||
+      Array.isArray(rawComponents)
+    ) {
+      errors.push({
+        tokenName: '_root',
+        severity: 'error',
+        message:
+          'Components configuration must be an object, not null, array, or primitive',
+      });
+      return { valid: false, errors, warnings };
+    }
+  }
+
+  // ERROR: algorithm must be a valid string or array of valid strings if present
+  // Valid values: "default", "dark", "system", "compact" (matches backend ThemeMode)
+  const rawAlgorithm = themeConfig.algorithm;
+  if (rawAlgorithm !== undefined) {
+    // Null is rejected by backend
+    if (rawAlgorithm === null) {
+      errors.push({
+        tokenName: '_root',
+        severity: 'error',
+        message: 'Algorithm cannot be null',
+      });
+      return { valid: false, errors, warnings };
+    }
+
+    // Must be string or array of strings
+    const isString = typeof rawAlgorithm === 'string';
+    const isStringArray =
+      Array.isArray(rawAlgorithm) &&
+      rawAlgorithm.every(a => typeof a === 'string');
+
+    if (!isString && !isStringArray) {
+      errors.push({
+        tokenName: '_root',
+        severity: 'error',
+        message:
+          'Algorithm must be a string or array of strings (e.g., "dark" or ["dark", "compact"])',
+      });
+      return { valid: false, errors, warnings };
+    }
+
+    // Validate algorithm values against allowed set
+    const algorithms = isString ? [rawAlgorithm] : (rawAlgorithm as string[]);
+    const invalidAlgorithms = algorithms.filter(
+      a => !VALID_ALGORITHM_VALUES.has(a),
+    );
+    if (invalidAlgorithms.length > 0) {
+      errors.push({
+        tokenName: '_root',
+        severity: 'error',
+        message: `Invalid algorithm value(s): "${invalidAlgorithms.join('", "')}". Valid values are: default, dark, system, compact`,
+      });
+      return { valid: false, errors, warnings };
+    }
+  }
+
+  Object.entries(tokens).forEach(([name, value]) => {
+    // Null/undefined check
+    if (value === null || value === undefined) {
+      warnings.push({
+        tokenName: name,
+        severity: 'warning',
+        message: `Token '${name}' has null/undefined value`,
+      });
+      return;
+    }
+
+    // Token name validation
+    if (!isValidTokenName(name)) {
+      warnings.push({
+        tokenName: name,
+        severity: 'warning',
+        message: `Unknown token '${name}' - may be ignored by Ant Design`,
+      });
+    }
+  });
+
+  return {
+    valid: errors.length === 0,
+    errors,
+    warnings,
+  };
+}