diff --git a/frontend/src/routes/admin/tags/+layout.svelte b/frontend/src/routes/admin/tags/+layout.svelte
index 190f5e29..9409e20f 100644
--- a/frontend/src/routes/admin/tags/+layout.svelte
+++ b/frontend/src/routes/admin/tags/+layout.svelte
@@ -8,7 +8,7 @@ const isAtListRoot = $derived(page.url.pathname === '/admin/tags');
 </script>
 
 <div class="{isAtListRoot ? 'flex' : 'hidden'} flex-shrink-0 md:flex">
-	<TagsListPanel tags={data.tags} />
+	<TagsListPanel tree={data.tree} />
 </div>
 
 <div class="{isAtListRoot ? 'hidden' : 'flex'} min-w-0 flex-1 flex-col overflow-hidden md:flex">
diff --git a/frontend/src/routes/admin/tags/TagTreeNode.svelte b/frontend/src/routes/admin/tags/TagTreeNode.svelte
new file mode 100644
index 00000000..e6e9c28d
--- /dev/null
+++ b/frontend/src/routes/admin/tags/TagTreeNode.svelte
@@ -0,0 +1,84 @@
+<script lang="ts">
+import { page } from '$app/state';
+import { SvelteMap } from 'svelte/reactivity';
+import { m } from '$lib/paraglide/messages.js';
+import type { components } from '$lib/generated/api';
+import TagTreeNode from './TagTreeNode.svelte';
+
+type TagTreeNodeDTO = components['schemas']['TagTreeNodeDTO'];
+
+let {
+	node,
+	depth,
+	collapseMap
+}: {
+	node: TagTreeNodeDTO;
+	depth: number;
+	collapseMap: SvelteMap<string, boolean>;
+} = $props();
+
+const hasChildren = $derived((node.children?.length ?? 0) > 0);
+const isCollapsed = $derived(collapseMap.get(node.id!) ?? false);
+const isActive = $derived(page.url.pathname.startsWith('/admin/tags/' + node.id));
+
+function toggleCollapse() {
+	collapseMap.set(node.id!, !isCollapsed);
+}
+</script>
+
+<li role="treeitem" aria-selected={isActive} aria-expanded={hasChildren ? !isCollapsed : undefined}>
+	<div class="flex items-center" style="padding-left: {depth * 12}px">
+		{#if hasChildren}
+			<button
+				onclick={toggleCollapse}
+				aria-label={isCollapsed ? m.admin_tag_expand_node() : m.admin_tag_collapse_node()}
+				class="flex min-h-[44px] min-w-[44px] items-center justify-center text-ink-3 transition-colors hover:text-ink"
+			>
+				<svg
+					class="h-3 w-3 transition-transform {isCollapsed ? '' : 'rotate-90'}"
+					viewBox="0 0 12 12"
+					fill="currentColor"
+					aria-hidden="true"
+				>
+					<path d="M4 2l4 4-4 4V2z" />
+				</svg>
+			</button>
+		{:else}
+			<button
+				class="invisible flex min-h-[44px] min-w-[44px] items-center justify-center"
+				tabindex="-1"
+				aria-hidden="true"
+			></button>
+		{/if}
+
+		{#if depth === 0 && node.color}
+			<span
+				data-testid="tag-list-color-dot"
+				data-color={node.color}
+				style="background-color: var(--c-tag-{node.color})"
+				class="mr-1.5 inline-block h-2 w-2 flex-shrink-0 rounded-full"
+			></span>
+		{/if}
+
+		<a
+			href="/admin/tags/{node.id}"
+			aria-current={isActive ? 'page' : undefined}
+			class="flex-1 truncate py-1 text-sm font-bold text-ink transition-colors hover:text-primary {isActive
+				? 'text-primary'
+				: ''}"
+		>
+			{node.name}
+			{#if (node.documentCount ?? 0) > 0}
+				<span class="ml-1 text-xs font-normal text-ink-3">({node.documentCount})</span>
+			{/if}
+		</a>
+	</div>
+
+	{#if hasChildren && !isCollapsed}
+		<ul role="group">
+			{#each node.children! as child (child.id)}
+				<TagTreeNode node={child} depth={depth + 1} collapseMap={collapseMap} />
+			{/each}
+		</ul>
+	{/if}
+</li>
diff --git a/frontend/src/routes/admin/tags/TagsListPanel.svelte b/frontend/src/routes/admin/tags/TagsListPanel.svelte
index a8bd95bc..c7dcc164 100644
--- a/frontend/src/routes/admin/tags/TagsListPanel.svelte
+++ b/frontend/src/routes/admin/tags/TagsListPanel.svelte
@@ -1,48 +1,42 @@
 <script lang="ts">
-import { page } from '$app/state';
 import { SvelteMap } from 'svelte/reactivity';
 import { m } from '$lib/paraglide/messages.js';
+import type { components } from '$lib/generated/api';
+import TagTreeNode from './TagTreeNode.svelte';
 
-type Tag = {
-	id: string;
-	name: string;
-	parentId?: string;
-	color?: string;
-};
-
-type TagWithDepth = Tag & { depth: number };
+type TagTreeNodeDTO = components['schemas']['TagTreeNodeDTO'];
 
 let {
-	tags,
+	tree,
 	autocollapse = false
 }: {
-	tags: Tag[];
+	tree: TagTreeNodeDTO[];
 	autocollapse?: boolean;
 } = $props();
 
-const orderedTags = $derived.by((): TagWithDepth[] => {
-	const roots = tags.filter((t) => !t.parentId);
-	const byParent = new SvelteMap<string, Tag[]>();
-	for (const t of tags) {
-		if (t.parentId) {
-			const arr = byParent.get(t.parentId) ?? [];
-			arr.push(t);
-			byParent.set(t.parentId, arr);
+function loadCollapseMap(): SvelteMap<string, boolean> {
+	if (typeof localStorage !== 'undefined') {
+		try {
+			const stored = localStorage.getItem('admin_tags_tree_state');
+			const parsed: Record<string, boolean> = stored ? JSON.parse(stored) : {};
+			return new SvelteMap(Object.entries(parsed));
+		} catch {
+			// ignore parse errors
 		}
 	}
-	const result: TagWithDepth[] = [];
-	function walk(node: Tag, depth: number) {
-		result.push({ ...node, depth });
-		for (const child of byParent.get(node.id) ?? []) {
-			walk(child, depth + 1);
+	return new SvelteMap();
+}
+
+const collapseMap = loadCollapseMap();
+
+$effect(() => {
+	if (typeof localStorage !== 'undefined') {
+		const obj: Record<string, boolean> = {};
+		for (const [k, v] of collapseMap) {
+			obj[k] = v;
 		}
+		localStorage.setItem('admin_tags_tree_state', JSON.stringify(obj));
 	}
-	for (const root of roots) walk(root, 0);
-	// Append orphan children (parent not in list)
-	for (const t of tags) {
-		if (!result.find((r) => r.id === t.id)) result.push({ ...t, depth: 0 });
-	}
-	return result;
 });
 
 let manualCollapse = $state(
@@ -74,13 +68,11 @@ $effect(() => {
 		</span>
 	</button>
 {:else}
-	<div
-		class="flex w-[200px] flex-shrink-0 flex-col overflow-hidden border-r border-line bg-surface"
-	>
+	<div class="flex w-60 flex-shrink-0 flex-col overflow-hidden border-r border-line bg-surface">
 		<!-- Panel header -->
 		<div class="flex items-center justify-between border-b border-line px-3 py-2">
 			<span class="text-xs font-bold tracking-widest text-ink-3 uppercase">
-				{m.admin_tags_list_title()}
+				{m.admin_tag_tree_label()}
 			</span>
 			<button
 				onclick={() => (manualCollapse = true)}
@@ -91,35 +83,18 @@ $effect(() => {
 			</button>
 		</div>
 
-		<!-- Scrollable tag list -->
+		<!-- Scrollable tag tree -->
 		<div class="flex-1 overflow-y-auto">
-			{#if tags.length === 0}
+			{#if tree.length === 0}
 				<p class="px-4 py-6 text-center text-xs text-ink-3">
 					{m.admin_tags_empty()}
 				</p>
 			{:else}
-				{#each orderedTags as tag (tag.id)}
-					{@const isActive = page.url.pathname.startsWith('/admin/tags/' + tag.id)}
-					<a
-						href="/admin/tags/{tag.id}"
-						aria-current={isActive ? 'page' : undefined}
-						class="block border-l-2 px-3 py-2.5 transition-colors {isActive
-							? 'border-primary bg-primary/10 dark:bg-primary/15'
-							: 'border-transparent hover:bg-muted'} {tag.depth > 0 ? 'pl-5' : ''}"
-					>
-						<div class="flex items-center text-sm font-bold text-ink">
-							{#if tag.color}
-								<span
-									data-testid="tag-list-color-dot"
-									data-color={tag.color}
-									style="background-color: var(--c-tag-{tag.color})"
-									class="mr-1.5 inline-block h-2 w-2 flex-shrink-0 rounded-full"
-								></span>
-							{/if}
-							{tag.name}
-						</div>
-					</a>
-				{/each}
+				<ul role="tree" aria-label={m.admin_tag_tree_label()}>
+					{#each tree as node (node.id)}
+						<TagTreeNode node={node} depth={0} collapseMap={collapseMap} />
+					{/each}
+				</ul>
 			{/if}
 		</div>
 	</div>
diff --git a/frontend/src/routes/admin/tags/layout.svelte.spec.ts b/frontend/src/routes/admin/tags/layout.svelte.spec.ts
index 7d3df2c3..058e8574 100644
--- a/frontend/src/routes/admin/tags/layout.svelte.spec.ts
+++ b/frontend/src/routes/admin/tags/layout.svelte.spec.ts
@@ -9,44 +9,97 @@ vi.mock('$app/state', () => ({
 
 afterEach(cleanup);
 
-const tags = [
-	{ id: 't1', name: 'Familie' },
-	{ id: 't2', name: 'Urlaub' },
-	{ id: 't3', name: 'Schule' }
+const tree = [
+	{
+		id: 't1',
+		name: 'Familie',
+		color: undefined,
+		documentCount: 3,
+		parentId: undefined,
+		children: [
+			{ id: 't2', name: 'Eltern', color: undefined, documentCount: 2, parentId: 't1', children: [] }
+		]
+	},
+	{
+		id: 't3',
+		name: 'Urlaub',
+		color: 'teal',
+		documentCount: 0,
+		parentId: undefined,
+		children: []
+	}
 ];
 
 describe('TagsListPanel — header', () => {
 	it('renders the panel title', async () => {
-		render(TagsListPanel, { tags });
-		await expect.element(page.getByText(/Alle Schlagworte/i)).toBeInTheDocument();
+		render(TagsListPanel, { tree });
+		await expect.element(page.getByText(/Schlagwörter/i)).toBeInTheDocument();
+	});
+});
+
+describe('TagsListPanel — ARIA tree', () => {
+	it('renders a role="tree" container', async () => {
+		const { container } = render(TagsListPanel, { tree });
+		expect(container.querySelector('[role="tree"]')).toBeTruthy();
+	});
+
+	it('renders role="treeitem" on each item', async () => {
+		const { container } = render(TagsListPanel, { tree });
+		const items = container.querySelectorAll('[role="treeitem"]');
+		// Both parent and child treeitem
+		expect(items.length).toBeGreaterThanOrEqual(2);
+	});
+
+	it('sets aria-expanded on nodes with children', async () => {
+		const { container } = render(TagsListPanel, { tree });
+		const familieItem = container.querySelector<HTMLElement>('[role="treeitem"]');
+		expect(familieItem?.hasAttribute('aria-expanded')).toBe(true);
+	});
+
+	it('does NOT set aria-expanded on leaf nodes', async () => {
+		const { container } = render(TagsListPanel, { tree });
+		const items = container.querySelectorAll<HTMLElement>('[role="treeitem"]');
+		const urlaubItem = Array.from(items).find((el) => el.textContent?.includes('Urlaub'));
+		expect(urlaubItem?.hasAttribute('aria-expanded')).toBe(false);
 	});
 });
 
 describe('TagsListPanel — tag items', () => {
-	it('renders each tag name', async () => {
-		render(TagsListPanel, { tags });
+	it('renders each root tag name as a link', async () => {
+		render(TagsListPanel, { tree });
 		await expect.element(page.getByRole('link', { name: /familie/i })).toBeInTheDocument();
 		await expect.element(page.getByRole('link', { name: /urlaub/i })).toBeInTheDocument();
 	});
 
 	it('each tag links to /admin/tags/[id]', async () => {
-		const { container } = render(TagsListPanel, { tags });
-		const links = container.querySelectorAll<HTMLAnchorElement>('a[href^="/admin/tags/t"]');
-		expect(links.length).toBe(3);
-		expect(links[0].getAttribute('href')).toBe('/admin/tags/t1');
+		const { container } = render(TagsListPanel, { tree });
+		const link = container.querySelector<HTMLAnchorElement>('a[href="/admin/tags/t1"]');
+		expect(link).toBeTruthy();
+	});
+
+	it('renders document count badge when documentCount > 0', async () => {
+		const { container } = render(TagsListPanel, { tree });
+		// Familie has count 3 — should show "(3)"
+		expect(container.textContent).toContain('(3)');
+	});
+
+	it('does not render count badge when documentCount is 0', async () => {
+		const { container } = render(TagsListPanel, { tree });
+		// Urlaub has count 0 — should NOT show "(0)"
+		expect(container.textContent).not.toContain('(0)');
 	});
 });
 
 describe('TagsListPanel — active state', () => {
 	it('marks the active tag link with aria-current=page', async () => {
-		render(TagsListPanel, { tags });
+		render(TagsListPanel, { tree });
 		await expect
 			.element(page.getByRole('link', { name: /familie/i }))
 			.toHaveAttribute('aria-current', 'page');
 	});
 
 	it('does not mark inactive tag links with aria-current', async () => {
-		render(TagsListPanel, { tags });
+		render(TagsListPanel, { tree });
 		await expect
 			.element(page.getByRole('link', { name: /urlaub/i }))
 			.not.toHaveAttribute('aria-current');
@@ -54,69 +107,52 @@ describe('TagsListPanel — active state', () => {
 });
 
 describe('TagsListPanel — empty state', () => {
-	it('shows empty state when tags array is empty', async () => {
-		render(TagsListPanel, { tags: [] });
+	it('shows empty state when tree is empty', async () => {
+		render(TagsListPanel, { tree: [] });
 		await expect.element(page.getByText(/keine schlagworte/i)).toBeInTheDocument();
 	});
 });
 
-// ─── Hierarchy rendering ──────────────────────────────────────────────────────
-
-describe('TagsListPanel — hierarchy', () => {
-	it('renders child tags indented under their parent', async () => {
-		render(TagsListPanel, {
-			tags: [
-				{ id: 't1', name: 'Immobilie' },
-				{ id: 't2', name: 'Haus', parentId: 't1' }
-			]
-		});
-		const childEl = document.querySelector<HTMLAnchorElement>('a[href="/admin/tags/t2"]');
-		expect(childEl?.className).toContain('pl-');
-	});
-
-	it('renders child after parent in the list', async () => {
-		render(TagsListPanel, {
-			tags: [
-				{ id: 't1', name: 'Immobilie' },
-				{ id: 't2', name: 'Haus', parentId: 't1' }
-			]
-		});
-		const links = document.querySelectorAll<HTMLAnchorElement>('a[href^="/admin/tags/t"]');
-		const hrefs = Array.from(links).map((l) => l.getAttribute('href'));
-		const parentIdx = hrefs.indexOf('/admin/tags/t1');
-		const childIdx = hrefs.indexOf('/admin/tags/t2');
-		expect(childIdx).toBeGreaterThan(parentIdx);
-	});
-
-	it('renders color dot on tags that have a color', async () => {
-		render(TagsListPanel, {
-			tags: [{ id: 't1', name: 'Immobilie', color: 'sage' }]
-		});
+describe('TagsListPanel — color dot', () => {
+	it('renders color dot on root tags that have a color', async () => {
+		render(TagsListPanel, { tree });
 		const dot = page.getByTestId('tag-list-color-dot');
 		await expect.element(dot).toBeInTheDocument();
-		await expect.element(dot).toHaveAttribute('data-color', 'sage');
+		await expect.element(dot).toHaveAttribute('data-color', 'teal');
 	});
 
 	it('does not render color dot on tags without a color', async () => {
-		render(TagsListPanel, { tags: [{ id: 't1', name: 'Familie' }] });
+		render(TagsListPanel, {
+			tree: [
+				{
+					id: 't1',
+					name: 'Familie',
+					documentCount: 0,
+					parentId: undefined,
+					children: [],
+					color: undefined
+				}
+			]
+		});
 		await expect.element(page.getByTestId('tag-list-color-dot')).not.toBeInTheDocument();
 	});
 });
 
-// ─── Collapse toggle ──────────────────────────────────────────────────────────
-
 describe('TagsListPanel — collapse toggle', () => {
-	beforeEach(() => localStorage.removeItem('admin_tags_list_collapsed'));
+	beforeEach(() => {
+		localStorage.removeItem('admin_tags_list_collapsed');
+		localStorage.removeItem('admin_tags_tree_state');
+	});
 
 	it('renders a collapse button with aria-label', async () => {
-		render(TagsListPanel, { tags });
+		render(TagsListPanel, { tree });
 		await expect
 			.element(page.getByRole('button', { name: /Liste einklappen/i }))
 			.toBeInTheDocument();
 	});
 
 	it('clicking collapse shows the expand handle', async () => {
-		render(TagsListPanel, { tags });
+		render(TagsListPanel, { tree });
 		await page.getByRole('button', { name: /Liste einklappen/i }).click();
 		await expect
 			.element(page.getByRole('button', { name: /Liste ausklappen/i }))
@@ -124,14 +160,14 @@ describe('TagsListPanel — collapse toggle', () => {
 	});
 
 	it('autocollapse prop starts the panel in collapsed state', async () => {
-		render(TagsListPanel, { tags, autocollapse: true });
+		render(TagsListPanel, { tree, autocollapse: true });
 		await expect
 			.element(page.getByRole('button', { name: /Liste ausklappen/i }))
 			.toBeInTheDocument();
 	});
 
 	it('persists collapse state using the tags-specific localStorage key', async () => {
-		render(TagsListPanel, { tags });
+		render(TagsListPanel, { tree });
 		const setSpy = vi.spyOn(Storage.prototype, 'setItem');
 		document.querySelector<HTMLButtonElement>('[aria-label="Liste einklappen"]')!.click();
 		await vi.waitFor(() =>
@@ -140,3 +176,29 @@ describe('TagsListPanel — collapse toggle', () => {
 		setSpy.mockRestore();
 	});
 });
+
+describe('TagsListPanel — chevron collapse', () => {
+	beforeEach(() => {
+		localStorage.removeItem('admin_tags_tree_state');
+		localStorage.removeItem('admin_tags_list_collapsed');
+	});
+
+	it('child items are visible by default', async () => {
+		render(TagsListPanel, { tree });
+		await expect.element(page.getByRole('link', { name: /eltern/i })).toBeInTheDocument();
+	});
+
+	it('clicking the chevron collapses children', async () => {
+		const { container } = render(TagsListPanel, { tree });
+		// Find the chevron button inside the Familie treeitem
+		const familieItem = Array.from(container.querySelectorAll('[role="treeitem"]')).find((el) =>
+			el.textContent?.includes('Familie')
+		);
+		const chevron = familieItem?.querySelector<HTMLButtonElement>('button[aria-label]');
+		chevron?.click();
+		await vi.waitFor(() => {
+			const eltern = container.querySelector('a[href="/admin/tags/t2"]');
+			expect(eltern).toBeFalsy();
+		});
+	});
+});