diff --git a/web/src/routes/(user)/utilities/duplicates/[[photos=photos]]/[[assetId=id]]/page.spec.ts b/web/src/routes/(user)/utilities/duplicates/[[photos=photos]]/[[assetId=id]]/page.spec.ts
new file mode 100644
index 000000000..66295067a
--- /dev/null
+++ b/web/src/routes/(user)/utilities/duplicates/[[photos=photos]]/[[assetId=id]]/page.spec.ts
@@ -0,0 +1,95 @@
+import { Route } from '#lib/route.ts';
+import { factory } from '#test/unit/factories.ts';
+import { test } from '#test/unit/fixtures.ts';
+import { expect } from 'vitest';
+import Page from './+page.svelte';
+import { load } from './+page.ts';
+
+test('stacking puts the asset chosen to keep first', async ({ data, router, render, settle, api, app }) => {
+  const assets = [factory.asset(), factory.asset(), factory.asset()];
+  data.addDuplicates(assets);
+  await router.goto(Route.duplicatesUtility());
+  await render(Page, load);
+
+  await app.duplicates.keepToggle(0).click();
+  await app.duplicates.keepToggle(1).click();
+  await app.duplicates.stackButton.click();
+  await settle();
+
+  expect(api.createStack).toHaveBeenCalledWith({ body: { assetIds: [assets[1].id, assets[0].id, assets[2].id] } });
+  expect(api.updateAssets).toHaveBeenCalledWith({
+    body: { ids: [assets[1].id, assets[0].id, assets[2].id], duplicateId: null },
+  });
+  await expect.element(app.duplicates.emptyMessage).toBeVisible();
+});
+
+test('resolving a group trashes the rest and shows the next', async ({ data, router, render, settle, api, app }) => {
+  const first = [factory.asset(), factory.asset()];
+  data.addDuplicates(first).addDuplicates([factory.asset(), factory.asset()]);
+  const [{ duplicateId }] = data.duplicateList();
+  await router.goto(Route.duplicatesUtility());
+  await render(Page, load);
+
+  await app.duplicates.trashButton.click();
+  await settle();
+
+  expect(api.resolveDuplicates).toHaveBeenCalledWith({
+    body: { groups: [{ duplicateId, keepAssetIds: [first[0].id], trashAssetIds: [first[1].id] }] },
+  });
+  await expect.element(app.duplicates.groupPosition(1, 1)).toBeVisible();
+});
+
+test('a group that fails to resolve stays', async ({ data, router, render, settle, api, logger, app }) => {
+  data.addDuplicates([factory.asset(), factory.asset()]);
+  api.on({ resolveDuplicates: ({ body }) => ({ json: [{ id: body.groups[0].duplicateId, success: false }] }) });
+  await router.goto(Route.duplicatesUtility());
+  await render(Page, load);
+
+  await app.duplicates.trashButton.click();
+  await settle();
+
+  expect(api.resolveDuplicates).toHaveBeenCalled();
+  expect(logger.error).toHaveBeenCalledWith(/handleError/);
+  await expect.element(app.duplicates.groupPosition(1, 1)).toBeVisible();
+});
+
+test('deduplicate all keeps the suggested assets', async ({ data, router, render, settle, api, app }) => {
+  const groups = [
+    [factory.asset(), factory.asset()],
+    [factory.asset(), factory.asset()],
+  ];
+  data.addDuplicates(groups[0]).addDuplicates(groups[1]);
+  const duplicateIds = data.duplicateList().map(({ duplicateId }) => duplicateId);
+  await router.goto(Route.duplicatesUtility());
+  await render(Page, load);
+
+  await app.duplicates.deduplicateAllButton.click();
+  await app.confirmButton.click();
+  await settle();
+
+  expect(api.resolveDuplicates).toHaveBeenCalledWith({
+    body: {
+      groups: groups.map((assets, index) => ({
+        duplicateId: duplicateIds[index],
+        keepAssetIds: [assets[0].id],
+        trashAssetIds: [assets[1].id],
+      })),
+    },
+  });
+  await expect.element(app.duplicates.emptyMessage).toBeVisible();
+});
+
+test('keep all clears every group without trashing', async ({ data, router, render, settle, api, app }) => {
+  data.addDuplicates([factory.asset(), factory.asset()]).addDuplicates([factory.asset(), factory.asset()]);
+  const ids = data.duplicateList().map(({ duplicateId }) => duplicateId);
+  await router.goto(Route.duplicatesUtility());
+  await render(Page, load);
+
+  await app.duplicates.keepAllButton.click();
+  await app.confirmButton.click();
+  await settle();
+
+  expect(api.deleteDuplicates).toHaveBeenCalledWith({ body: { ids } });
+  expect(api.resolveDuplicates).not.toHaveBeenCalled();
+  await expect.element(app.duplicates.emptyMessage).toBeVisible();
+});
diff --git a/web/test/common/data.ts b/web/test/common/data.ts
index 2a0e951db..754341748 100644
--- a/web/test/common/data.ts
+++ b/web/test/common/data.ts
@@ -15,6 +15,7 @@ import {
   type AssetResponseDto,
   type CreateAlbumDto,
   type DownloadInfoDto,
+  type DuplicateResolveDto,
   type DuplicateResponseDto,
   type MapMarkerResponseDto,
   type MemoryResponseDto,
@@ -24,7 +25,9 @@ import {
   type PluginMethodResponseDto,
   type SearchResponseDto,
   type SharedLinkResponseDto,
+  type StackCreateDto,
   type StackResponseDto,
+  type StackUpdateDto,
   type TagResponseDto,
   type TimeBucketAssetResponseDto,
   type TimeBucketsResponseDto,
@@ -352,6 +355,23 @@ export class MockData {
     return [...groups].map(([duplicateId, assets]) => ({ duplicateId, assets, suggestedKeepAssetIds: [assets[0].id] }));
   }
 
+  resolveDuplicates({ groups }: DuplicateResolveDto) {
+    for (const { duplicateId, trashAssetIds } of groups) {
+      this.deleteDuplicates([duplicateId]);
+      this.deleteAssets(trashAssetIds);
+    }
+    return groups.map(({ duplicateId }) => ({ id: duplicateId, success: true }));
+  }
+
+  deleteDuplicates(duplicateIds: string[]) {
+    const ids = new Set(duplicateIds);
+    const duplicates = [...this.assets.values()].filter(({ duplicateId }) => duplicateId && ids.has(duplicateId));
+    for (const asset of duplicates) {
+      this.assets.set(asset.id, { ...asset, duplicateId: null });
+    }
+    return this;
+  }
+
   removeFromAlbum(albumId: string, assetIds: string[]) {
     const members = this.albumAssets.get(albumId);
     return assetIds.map((id) => ({ id, success: members?.delete(id) ?? false }));
@@ -475,6 +495,43 @@ export class MockData {
     return this;
   }
 
+  createStack({ assetIds }: StackCreateDto) {
+    const stack = factory.stack({ assets: assetIds.map((id) => this.assets.get(id)!) });
+    this.addStacks(stack);
+    return stack;
+  }
+
+  updateStack(id: string, { primaryAssetId }: StackUpdateDto) {
+    const stack = this.stacks.get(id);
+    if (!stack) {
+      return;
+    }
+    const updated = { ...stack, primaryAssetId: primaryAssetId ?? stack.primaryAssetId };
+    this.stacks.set(id, updated);
+    return updated;
+  }
+
+  removeFromStack(id: string, assetId: string) {
+    const stack = this.stacks.get(id);
+    const asset = this.assets.get(assetId);
+    if (!stack || !asset) {
+      return;
+    }
+    this.stacks.set(id, { ...stack, assets: stack.assets.filter((asset) => asset.id !== assetId) });
+    this.assets.set(assetId, { ...asset, stack: null });
+    return this;
+  }
+
+  deleteStacks(ids: string[]) {
+    for (const id of ids) {
+      for (const asset of this.stacks.get(id)?.assets ?? []) {
+        this.assets.set(asset.id, { ...asset, stack: null });
+      }
+      this.stacks.delete(id);
+    }
+    return this;
+  }
+
   addOcr(results: MaybeArray<AssetOcrResponseDto>) {
     for (const result of toList(results)) {
       const existing = this.ocr.get(result.assetId) ?? [];
diff --git a/web/test/common/handlers.ts b/web/test/common/handlers.ts
index 1a705c3ef..cbc1491da 100644
--- a/web/test/common/handlers.ts
+++ b/web/test/common/handlers.ts
@@ -78,6 +78,11 @@ export const createHandlers = (data: MockData): Handlers => {
       json: { results: body.assets.map(({ id }) => ({ id, action: AssetUploadAction.Accept })) },
     }),
     getAssetDuplicates: () => ({ json: data.duplicateList() }),
+    resolveDuplicates: ({ body }) => ({ json: data.resolveDuplicates(body) }),
+    deleteDuplicates: ({ body }) => {
+      data.deleteDuplicates(body.ids);
+      return { status: 204 };
+    },
 
     getActivities: ({ params }) => ({ json: data.activityList(params) }),
     getActivityStatistics: ({ params }) => ({ json: data.activityStatistics(params) }),
@@ -106,6 +111,17 @@ export const createHandlers = (data: MockData): Handlers => {
       const stack = data.getStack(params.id);
       return stack ? { json: stack } : notFound;
     },
+    createStack: ({ body }) => ({ status: 201, json: data.createStack(body) }),
+    updateStack: ({ params, body }) => {
+      const stack = data.updateStack(params.id, body);
+      return stack ? { json: stack } : notFound;
+    },
+    removeAssetFromStack: ({ params }) =>
+      data.removeFromStack(params.id, params.assetId) ? { status: 204 } : notFound,
+    deleteStacks: ({ body }) => {
+      data.deleteStacks(body.ids);
+      return { status: 204 };
+    },
 
     getAllAlbums: ({ params = {} }) => ({ json: data.albumList(params.assetId) }),
     createAlbum: ({ body }) => ({ status: 201, json: data.createAlbum(body) }),
diff --git a/web/test/medium/app.ts b/web/test/medium/app.ts
index 88a54d1ea..8765c5d89 100644
--- a/web/test/medium/app.ts
+++ b/web/test/medium/app.ts
@@ -178,6 +178,16 @@ const createTimeline = (page: Page, data: MockData) => {
         await page.getByRole('menuitem', { name: 'change_date', exact: true }).click();
       },
 
+      stack: async () => {
+        await page.getByLabel('menu', { exact: true }).click();
+        await page.getByRole('menuitem', { name: 'stack', exact: true }).click();
+      },
+
+      unstack: async () => {
+        await page.getByLabel('menu', { exact: true }).click();
+        await page.getByRole('menuitem', { name: 'unstack', exact: true }).click();
+      },
+
       removeFromAlbum: async () => {
         await page.getByLabel('menu', { exact: true }).click();
         await page.getByRole('menuitem', { name: 'remove_from_album', exact: true }).click();
@@ -336,6 +346,9 @@ const createViewer = (page: Page) => {
     download: () => moreMenuItem('download'),
     archive: () => moreMenuItem('to_archive'),
     unarchive: () => moreMenuItem('unarchive'),
+    unstack: () => moreMenuItem('unstack'),
+    setStackPrimary: () => moreMenuItem('set_stack_primary_asset'),
+    removeFromStack: () => moreMenuItem('viewer_remove_from_stack'),
 
     permanentlyDelete: async () => {
       await page.getByLabel('permanently_delete', { exact: true }).click();
diff --git a/web/test/medium/specs/asset-viewer/stack.spec.ts b/web/test/medium/specs/asset-viewer/stack.spec.ts
index b0d1ab8e3..e795eafb4 100644
--- a/web/test/medium/specs/asset-viewer/stack.spec.ts
+++ b/web/test/medium/specs/asset-viewer/stack.spec.ts
@@ -2,21 +2,105 @@ import { Route } from '#lib/route.ts';
 import { factory } from '#test/common/factories.ts';
 import { expect, test } from '#test/medium/fixtures.ts';
 
-test('stack strip lists the stack and the detail panel follows the selected asset', async ({ page, data, app }) => {
-  const primary = factory.asset({ tags: [factory.tag({ name: '1', value: 'test/1' })] });
-  const second = factory.asset({ tags: [factory.tag({ name: '2', value: 'test/2' })] });
-  data
-    .addStacks(factory.stack({ assets: [primary, second] }))
-    .setPreferences(factory.preferences({ tags: { enabled: true, sidebarWeb: false } }));
-  await page.goto(Route.viewAsset({ id: primary.id }));
-  await app.viewer.waitForAsset(primary);
+test.describe('stack', () => {
+  test('stack strip lists the stack and the detail panel follows the selected asset', async ({ page, data, app }) => {
+    const primary = factory.asset({ tags: [factory.tag({ name: '1', value: 'test/1' })] });
+    const second = factory.asset({ tags: [factory.tag({ name: '2', value: 'test/2' })] });
+    data
+      .addStacks(factory.stack({ assets: [primary, second] }))
+      .setPreferences(factory.preferences({ tags: { enabled: true, sidebarWeb: false } }));
+    await page.goto(Route.viewAsset({ id: primary.id }));
+    await app.viewer.waitForAsset(primary);
 
-  await expect(app.viewer.stack).toBeVisible();
-  await expect(app.viewer.stackAssets).toHaveCount(2);
+    await expect(app.viewer.stack).toBeVisible();
+    await expect(app.viewer.stackAssets).toHaveCount(2);
 
-  await app.viewer.openDetailPanel();
-  await expect(app.viewer.tags.first()).toHaveText('test/1');
+    await app.viewer.openDetailPanel();
+    await expect(app.viewer.tags.first()).toHaveText('test/1');
 
-  await app.viewer.stackThumbnail(second).click();
-  await expect(app.viewer.tags.first()).toHaveText('test/2');
+    await app.viewer.stackThumbnail(second).click();
+    await expect(app.viewer.tags.first()).toHaveText('test/2');
+  });
+
+  test('stack strip is hidden during a slideshow', async ({ page, data, app }) => {
+    const [primary, second] = [factory.asset(), factory.asset()];
+    data.addStacks(factory.stack({ assets: [primary, second] }));
+    await page.goto(Route.viewAsset({ id: primary.id }));
+    await app.viewer.waitForAsset(primary);
+    await expect(app.viewer.stack).toBeVisible();
+
+    await app.viewer.openSlideshow();
+
+    await expect(app.viewer.exitSlideshowButton).toBeVisible();
+    await expect(app.viewer.stack).not.toBeVisible();
+  });
+
+  test('stacking selected assets from the timeline', async ({ page, data, api, app }) => {
+    const [first, second] = [factory.asset(), factory.asset()];
+    data.addAssets([first, second]);
+    await page.goto(Route.photos());
+    await app.timeline.select(first);
+    await app.timeline.select(second);
+
+    await app.timeline.selectionBar.stack();
+
+    expect(api.createStack).toHaveBeenCalledWith({ body: { assetIds: [first.id, second.id] } });
+    await expect(app.toast('stacked_assets_count')).toBeVisible();
+    await expect(app.timeline.selected).toHaveCount(0);
+  });
+
+  test('unstacking selected assets from the timeline', async ({ page, data, api, app }) => {
+    const stack = factory.stack({ assets: [factory.asset(), factory.asset()] });
+    data.addStacks(stack);
+    await page.goto(Route.photos());
+    await app.timeline.select(stack.assets[0]);
+
+    await app.timeline.selectionBar.unstack();
+
+    expect(api.deleteStacks).toHaveBeenCalledWith({ body: { ids: [stack.id] } });
+    await expect(app.toast('unstacked_assets_count')).toBeVisible();
+    await expect(app.timeline.selected).toHaveCount(0);
+  });
+
+  test('unstacking from the viewer closes it', async ({ page, data, api, app }) => {
+    const stack = factory.stack({ assets: [factory.asset(), factory.asset()] });
+    data.addStacks(stack);
+    await page.goto(Route.viewAsset({ id: stack.assets[0].id }));
+    await app.viewer.waitForAsset(stack.assets[0]);
+
+    await app.viewer.unstack();
+
+    expect(api.deleteStacks).toHaveBeenCalledWith({ body: { ids: [stack.id] } });
+    await expect(app.toast('unstacked_assets_count')).toBeVisible();
+    await expect(app.viewer.root).not.toBeVisible();
+  });
+
+  test('removing an asset from the stack drops it from the strip', async ({ page, data, api, app }) => {
+    const stack = factory.stack({ assets: [factory.asset(), factory.asset(), factory.asset()] });
+    data.addStacks(stack);
+    const removed = stack.assets[1];
+    await page.goto(Route.viewAsset({ id: removed.id }));
+    await app.viewer.waitForAsset(removed);
+
+    await app.viewer.removeFromStack();
+
+    expect(api.removeAssetFromStack).toHaveBeenCalledWith({ params: { id: stack.id, assetId: removed.id } });
+    await expect(app.toast('removed_from_stack')).toBeVisible();
+    await expect(app.viewer.stackAssets).toHaveCount(2);
+    await expect(app.viewer.stackThumbnail(removed)).toHaveCount(0);
+  });
+
+  test('setting the primary asset of a stack', async ({ page, data, api, app }) => {
+    const stack = factory.stack({ assets: [factory.asset(), factory.asset()] });
+    data.addStacks(stack);
+    const second = stack.assets[1];
+    await page.goto(Route.viewAsset({ id: second.id }));
+    await app.viewer.waitForAsset(second);
+
+    await app.viewer.setStackPrimary();
+
+    expect(api.updateStack).toHaveBeenCalledWith({ params: { id: stack.id }, body: { primaryAssetId: second.id } });
+    await app.viewer.moreButton.click();
+    await expect(page.getByRole('menuitem', { name: 'set_stack_primary_asset', exact: true })).toHaveCount(0);
+  });
 });
diff --git a/web/test/unit/app.ts b/web/test/unit/app.ts
index 4327df826..d184ae627 100644
--- a/web/test/unit/app.ts
+++ b/web/test/unit/app.ts
@@ -46,6 +46,16 @@ export const createApp = () => {
         removeMenuItem: page.getByRole('menuitem', { name: 'remove', exact: true }),
       },
     },
+    confirmButton: page.getByRole('dialog').getByRole('button', { name: 'confirm', exact: true }),
+    duplicates: {
+      keepToggle: (index: number) => button('keep').nth(index),
+      stackButton: button('stack'),
+      trashButton: button('trash_count'),
+      deduplicateAllButton: button('deduplicate_all'),
+      keepAllButton: button('keep_all').first(),
+      groupPosition: (current: number, total: number) => page.getByText(`${current} / ${total}`),
+      emptyMessage: page.getByText('no_duplicates_found'),
+    },
     trash: {
       emptyTrashButton: button('empty_trash'),
       restoreAllButton: button('restore_all'),