diff --git a/plugins/setting-resources/src/__tests__/attributeUsage.test.ts b/plugins/setting-resources/src/__tests__/attributeUsage.test.ts
new file mode 100644
index 00000000000..b392d70d783
--- /dev/null
+++ b/plugins/setting-resources/src/__tests__/attributeUsage.test.ts
@@ -0,0 +1,48 @@
+//
+// Copyright © 2026 Hardcore Engineering Inc.
+//
+// Licensed under the Eclipse Public 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 https://www.eclipse.org/legal/epl-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 { AnyAttribute, Class, Doc, Domain, Ref } from '@hcengineering/core'
+import { isAttributeUsed } from '../attributeUsage'
+
+function makeClient (domain: Domain | undefined, found: Doc | undefined): any {
+  return {
+    getHierarchy: () => ({ findDomain: jest.fn(() => domain) }),
+    findOne: jest.fn(async () => found)
+  }
+}
+
+const attribute: Pick<AnyAttribute, 'attributeOf' | 'name'> = {
+  attributeOf: 'test:mixin:Custom' as Ref<Class<Doc>>,
+  name: 'custom1'
+}
+
+describe('isAttributeUsed', () => {
+  it('queries the attribute class when it has a domain', async () => {
+    const client = makeClient('task' as Domain, { _id: 'doc1' } as unknown as Doc)
+    expect(await isAttributeUsed(client, attribute)).toBe(true)
+    expect(client.findOne).toHaveBeenCalledWith(attribute.attributeOf, { custom1: { $exists: true } })
+  })
+
+  it('returns false when no document has the attribute', async () => {
+    const client = makeClient('task' as Domain, undefined)
+    expect(await isAttributeUsed(client, attribute)).toBe(false)
+  })
+
+  it('does not query a domainless class and treats the attribute as used', async () => {
+    const client = makeClient(undefined, undefined)
+    expect(await isAttributeUsed(client, attribute)).toBe(true)
+    expect(client.findOne).not.toHaveBeenCalled()
+  })
+})
diff --git a/plugins/setting-resources/src/attributeUsage.ts b/plugins/setting-resources/src/attributeUsage.ts
new file mode 100644
index 00000000000..ed5dcf00dcb
--- /dev/null
+++ b/plugins/setting-resources/src/attributeUsage.ts
@@ -0,0 +1,34 @@
+//
+// Copyright © 2026 Hardcore Engineering Inc.
+//
+// Licensed under the Eclipse Public 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 https://www.eclipse.org/legal/epl-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 { AnyAttribute, Client } from '@hcengineering/core'
+
+/**
+ * Check whether any document has a value for the attribute.
+ *
+ * Mixins declared on a domainless class (e.g. a mixin on core.class.Doc) can be
+ * applied to documents of any domain, so they cannot be queried directly. The
+ * attribute is treated as used in that case, which keeps its type locked and
+ * shows the stronger delete confirmation.
+ */
+export async function isAttributeUsed (
+  client: Pick<Client, 'findOne' | 'getHierarchy'>,
+  attribute: Pick<AnyAttribute, 'attributeOf' | 'name'>
+): Promise<boolean> {
+  if (client.getHierarchy().findDomain(attribute.attributeOf) === undefined) {
+    return true
+  }
+  return (await client.findOne(attribute.attributeOf, { [attribute.name]: { $exists: true } })) !== undefined
+}
diff --git a/plugins/setting-resources/src/components/ClassAttributes.svelte b/plugins/setting-resources/src/components/ClassAttributes.svelte
index b4be28df36a..0eb6a456b73 100644
--- a/plugins/setting-resources/src/components/ClassAttributes.svelte
+++ b/plugins/setting-resources/src/components/ClassAttributes.svelte
@@ -33,6 +33,7 @@
   import { ObjectPresenter } from '@hcengineering/view-resources'
   import { onDestroy } from 'svelte'
   import settings from '../plugin'
+  import { isAttributeUsed } from '../attributeUsage'
   import { clearSettingsStore, settingsStore } from '../store'
   import ClassAttributesList from './ClassAttributesList.svelte'
   import CreateAttribute from './CreateAttribute.svelte'
@@ -147,7 +148,7 @@
   const handleSelect = async (event: CustomEvent): Promise<void> => {
     selected = event.detail as AnyAttribute
     if (selected?._id != null) {
-      const exist = (await client.findOne(selected.attributeOf, { [selected.name]: { $exists: true } })) !== undefined
+      const exist = await isAttributeUsed(client, selected)
       $settingsStore = {
         id: selected._id,
         component: EditAttribute,
diff --git a/plugins/setting-resources/src/components/ClassAttributesList.svelte b/plugins/setting-resources/src/components/ClassAttributesList.svelte
index e65ab2cfc9a..0d6870f00ac 100644
--- a/plugins/setting-resources/src/components/ClassAttributesList.svelte
+++ b/plugins/setting-resources/src/components/ClassAttributesList.svelte
@@ -40,6 +40,7 @@
   } from '@hcengineering/ui'
   import { getContextActions, SortableList } from '@hcengineering/view-resources'
   import settings from '../plugin'
+  import { isAttributeUsed } from '../attributeUsage'
   import ClassAttributeRow from './ClassAttributeRow.svelte'
   import { makeRank } from '@hcengineering/rank'
   import EditAttribute from './EditAttribute.svelte'
@@ -133,7 +134,7 @@
 
   async function showMenu (ev: MouseEvent, attribute: AnyAttribute): Promise<void> {
     hovered = attribute._id
-    const exist = (await client.findOne(attribute.attributeOf, { [attribute.name]: { $exists: true } })) !== undefined
+    const exist = await isAttributeUsed(client, attribute)
     const actions: Action[] = [
       {
         label: presentation.string.Edit,