diff --git a/apps/api/src/routes/cards.ts b/apps/api/src/routes/cards.ts
index 9243b45..77d1e7f 100644
--- a/apps/api/src/routes/cards.ts
+++ b/apps/api/src/routes/cards.ts
@@ -1,7 +1,13 @@
 import { and, eq } from 'drizzle-orm';
 import { Hono } from 'hono';
 
-import { CardCreateSchema, CardUpdateSchema, newReview, subIndexCount } from '@cards/domain';
+import {
+	CardCreateSchema,
+	CardUpdateSchema,
+	newReview,
+	subIndexCount,
+	subIndexCountForCloze,
+} from '@cards/domain';
 
 import { getDb, type CardsDb } from '../db/connection.ts';
 import { cards, decks, reviews } from '../db/schema/index.ts';
@@ -33,6 +39,22 @@ export function cardsRouter(deps: CardsDeps = {}): Hono<{ Variables: AuthVars }>
 		}
 		const userId = c.get('userId');
 
+		// Cloze: Sub-Index-Anzahl hängt vom Cluster-Markup im Text ab.
+		// Eine Cloze-Karte ohne `{{cN::…}}` ist sinnlos — vor dem Deck-Lookup
+		// ablehnen, damit Validation-Errors konsistent 422 statt 404 sind.
+		let count: number;
+		if (parsed.data.type === 'cloze') {
+			count = subIndexCountForCloze(parsed.data.fields.text ?? '');
+			if (count === 0) {
+				return c.json(
+					{ error: 'invalid_input', issues: ['cloze.text contains no {{cN::…}} clusters'] },
+					422
+				);
+			}
+		} else {
+			count = subIndexCount(parsed.data.type);
+		}
+
 		const [deck] = await dbOf()
 			.select({ id: decks.id, userId: decks.userId })
 			.from(decks)
@@ -43,7 +65,7 @@ export function cardsRouter(deps: CardsDeps = {}): Hono<{ Variables: AuthVars }>
 
 		const cardId = ulid();
 		const now = new Date();
-		const subIndices = Array.from({ length: subIndexCount(parsed.data.type) }, (_, i) => i);
+		const subIndices = Array.from({ length: count }, (_, i) => i);
 
 		const [cardRow] = await dbOf().transaction(async (tx) => {
 			const [card] = await tx
diff --git a/apps/api/tests/cards.test.ts b/apps/api/tests/cards.test.ts
index d8bce5f..0658d22 100644
--- a/apps/api/tests/cards.test.ts
+++ b/apps/api/tests/cards.test.ts
@@ -62,13 +62,59 @@ describe('cardsRouter — Input-Validation', () => {
 			headers: { 'X-User-Id': 'u-1', 'Content-Type': 'application/json' },
 			body: JSON.stringify({
 				deck_id: 'd-1',
-				type: 'cloze',
-				fields: { text: 'x' },
+				type: 'image-occlusion',
+				fields: { image_ref: 'x', mask_regions: 'y' },
 			}),
 		});
 		expect(res.status).toBe(422);
 	});
 
+	it('POST mit cloze-Card ohne text-Feld ist 422', async () => {
+		const { app } = buildApp();
+		const res = await app.request('/api/v1/cards', {
+			method: 'POST',
+			headers: { 'X-User-Id': 'u-1', 'Content-Type': 'application/json' },
+			body: JSON.stringify({
+				deck_id: 'd-1',
+				type: 'cloze',
+				fields: {},
+			}),
+		});
+		expect(res.status).toBe(422);
+	});
+
+	it('POST mit cloze-Card aber Text ohne Cluster ist 422', async () => {
+		const { app } = buildApp();
+		const res = await app.request('/api/v1/cards', {
+			method: 'POST',
+			headers: { 'X-User-Id': 'u-1', 'Content-Type': 'application/json' },
+			body: JSON.stringify({
+				deck_id: 'd-1',
+				type: 'cloze',
+				fields: { text: 'plain text without any {{cN::…}} markup' },
+			}),
+		});
+		expect(res.status).toBe(422);
+		const body = (await res.json()) as { error: string; issues: string[] };
+		expect(body.issues[0]).toMatch(/cloze\.text/);
+	});
+
+	it('POST mit gültiger cloze-Card erreicht Deck-Lookup (404 bei stub)', async () => {
+		const { app } = buildApp();
+		const res = await app.request('/api/v1/cards', {
+			method: 'POST',
+			headers: { 'X-User-Id': 'u-1', 'Content-Type': 'application/json' },
+			body: JSON.stringify({
+				deck_id: 'd-1',
+				type: 'cloze',
+				fields: { text: 'Capital of {{c1::France}} is {{c2::Paris}}.' },
+			}),
+		});
+		expect(res.status).toBe(404);
+		const body = (await res.json()) as { error: string };
+		expect(body.error).toBe('deck_not_found');
+	});
+
 	it('PATCH mit extra prop ist 422', async () => {
 		const { app } = buildApp();
 		const res = await app.request('/api/v1/cards/c-1', {
diff --git a/packages/cards-domain/src/cloze.ts b/packages/cards-domain/src/cloze.ts
new file mode 100644
index 0000000..6272a2f
--- /dev/null
+++ b/packages/cards-domain/src/cloze.ts
@@ -0,0 +1,69 @@
+/**
+ * Cloze-Helpers: Cluster-Extraktion + Sub-Index-Mapping.
+ *
+ * Anki-Cloze-Markup: `{{cN::answer}}` oder `{{cN::answer::hint}}`. N ist
+ * eine 1-basierte Cluster-ID — alle Vorkommen mit gleichem N gehören zum
+ * selben Cluster (= ein Review). Mehrere Cluster pro Karte → mehrere
+ * Sub-Index-Reviews.
+ *
+ * Hint (`::hint`) wird MVP-stumm fallengelassen — Anki zeigt ihn unter
+ * der Maske, das ist Polish-Phase.
+ */
+
+const CLUSTER_RE = /\{\{c(\d+)::([^}]*?)(?:::([^}]*?))?\}\}/g;
+
+/**
+ * Extrahiert distinct Cluster-IDs (sortiert). Aus `{{c2::a}} {{c1::b}} {{c2::c}}`
+ * wird `[1, 2]`. Leeres Result, wenn kein Cluster-Markup im Text.
+ */
+export function extractClusterIds(text: string): number[] {
+	const ids = new Set<number>();
+	for (const match of text.matchAll(CLUSTER_RE)) {
+		const n = Number(match[1]);
+		if (Number.isInteger(n) && n >= 1) ids.add(n);
+	}
+	return [...ids].sort((a, b) => a - b);
+}
+
+/**
+ * Wie viele Reviews braucht eine Cloze-Karte? Ein Review pro distinct
+ * Cluster-ID. Gibt 0 zurück, wenn der Text gar kein Cluster-Markup enthält
+ * — der Caller muss diesen Fall als Validation-Error behandeln, weil eine
+ * Cloze-Karte ohne Cluster sinnlos wäre.
+ */
+export function subIndexCountForCloze(text: string): number {
+	return extractClusterIds(text).length;
+}
+
+/**
+ * Mapping Sub-Index → Cluster-ID. Sub-Index 0 = niedrigste Cluster-ID,
+ * 1 = nächste, usw. Für den Card-Insert-Pfad und das Study-Render.
+ */
+export function clusterIdForSubIndex(text: string, subIndex: number): number | null {
+	const ids = extractClusterIds(text);
+	return ids[subIndex] ?? null;
+}
+
+/**
+ * Render-Helper für den Prompt: aktiver Cluster wird zu `[…]`, alle
+ * anderen Cluster werden auf ihre Antwort expandiert. Hint (`::hint`)
+ * wird gedroppt.
+ */
+export function renderClozePrompt(text: string, activeClusterId: number): string {
+	return text.replace(CLUSTER_RE, (_, nStr: string, answer: string) => {
+		const n = Number(nStr);
+		return n === activeClusterId ? '[…]' : answer;
+	});
+}
+
+/**
+ * Render-Helper für die Antwort: alle Cluster werden expandiert. Aktiver
+ * Cluster wird optisch markiert (Markdown-Bold), damit der User sieht,
+ * was er gerade beantworten sollte.
+ */
+export function renderClozeAnswer(text: string, activeClusterId: number): string {
+	return text.replace(CLUSTER_RE, (_, nStr: string, answer: string) => {
+		const n = Number(nStr);
+		return n === activeClusterId ? `**${answer}**` : answer;
+	});
+}
diff --git a/packages/cards-domain/src/fsrs.ts b/packages/cards-domain/src/fsrs.ts
index 3b1b019..0c29cc3 100644
--- a/packages/cards-domain/src/fsrs.ts
+++ b/packages/cards-domain/src/fsrs.ts
@@ -130,8 +130,10 @@ export function fromFsrsCard(prev: Review, fc: FsrsCard): Review {
  * um die `(card_id, sub_index)`-Reihen zu initialisieren.
  *
  * Cloze ist Sonderfall: `subIndex` hängt von der Anzahl der Cluster
- * im `fields.text` ab; `subIndexCountForCloze(text)` muss separat
- * gerufen werden, sobald wir Cloze unterstützen.
+ * im `fields.text` ab. Für Cloze MUSS der Caller `subIndexCountForCloze`
+ * aus `./cloze.ts` rufen — diese Funktion wirft, weil ein stiller
+ * Default-Fallback (z.B. 1) zu falsch dimensionierten Review-Tabellen
+ * führen würde.
  */
 export function subIndexCount(type: string): number {
 	switch (type) {
@@ -147,6 +149,10 @@ export function subIndexCount(type: string): number {
 			return 1;
 		case 'multiple-choice':
 			return 1;
+		case 'cloze':
+			throw new Error(
+				'subIndexCount("cloze") not supported — use subIndexCountForCloze(text) from @cards/domain'
+			);
 		default:
 			return 1;
 	}
diff --git a/packages/cards-domain/src/index.ts b/packages/cards-domain/src/index.ts
index 4d82e68..e6096fb 100644
--- a/packages/cards-domain/src/index.ts
+++ b/packages/cards-domain/src/index.ts
@@ -10,4 +10,4 @@
 export * from './schemas/index.ts';
 export * from './fsrs.ts';
 export * from './protocol/index.ts';
-// export * from './cloze.ts';  // Phase 8 oder später: Cloze-Parser
+export * from './cloze.ts';
diff --git a/packages/cards-domain/src/schemas/card.ts b/packages/cards-domain/src/schemas/card.ts
index 13dc44d..45b6e0c 100644
--- a/packages/cards-domain/src/schemas/card.ts
+++ b/packages/cards-domain/src/schemas/card.ts
@@ -1,10 +1,11 @@
 import { z } from 'zod';
 
 /**
- * MVP-CardType-Set. Erweiterung in CARDS_GREENFIELD.md Phase 8+ vorgesehen
- * (cloze, type-in, image-occlusion, audio, multiple-choice).
+ * MVP-CardType-Set. Cloze in Phase 8 (Anki-Import) ergänzt; weitere
+ * Erweiterung (type-in, image-occlusion, audio, multiple-choice)
+ * vorbereitet im CardTypeFutureSchema.
  */
-export const CardTypeSchema = z.enum(['basic', 'basic-reverse']);
+export const CardTypeSchema = z.enum(['basic', 'basic-reverse', 'cloze']);
 export type CardType = z.infer<typeof CardTypeSchema>;
 
 /** Future-Set für Schema-Migration-Vorbereitung. */
diff --git a/packages/cards-domain/tests/cloze.test.ts b/packages/cards-domain/tests/cloze.test.ts
new file mode 100644
index 0000000..8a030d8
--- /dev/null
+++ b/packages/cards-domain/tests/cloze.test.ts
@@ -0,0 +1,74 @@
+import { describe, it, expect } from 'vitest';
+
+import {
+	extractClusterIds,
+	subIndexCountForCloze,
+	clusterIdForSubIndex,
+	renderClozePrompt,
+	renderClozeAnswer,
+} from '../src/cloze.ts';
+
+describe('extractClusterIds', () => {
+	it('liefert leere Liste, wenn kein Cluster-Markup', () => {
+		expect(extractClusterIds('Plain text without cloze')).toEqual([]);
+	});
+
+	it('extrahiert einen einzelnen Cluster', () => {
+		expect(extractClusterIds('The capital of France is {{c1::Paris}}.')).toEqual([1]);
+	});
+
+	it('extrahiert mehrere Cluster aufsteigend sortiert', () => {
+		expect(extractClusterIds('{{c2::B}} kommt nach {{c1::A}}')).toEqual([1, 2]);
+	});
+
+	it('dedupliziert mehrfach auftretende Cluster-IDs', () => {
+		expect(extractClusterIds('{{c1::a}} und {{c1::b}} und {{c2::c}}')).toEqual([1, 2]);
+	});
+
+	it('ignoriert malformed Cluster (kein numerisches N)', () => {
+		expect(extractClusterIds('{{cX::weird}} {{c1::ok}}')).toEqual([1]);
+	});
+
+	it('akzeptiert Cluster mit Hint (::hint wird gedroppt)', () => {
+		expect(extractClusterIds('Die {{c1::Hauptstadt::Land}} von Frankreich.')).toEqual([1]);
+	});
+});
+
+describe('subIndexCountForCloze', () => {
+	it('zählt distinct Cluster', () => {
+		expect(subIndexCountForCloze('{{c1::a}} {{c2::b}} {{c3::c}}')).toBe(3);
+	});
+
+	it('returniert 0 bei text ohne Cluster', () => {
+		expect(subIndexCountForCloze('keine cloze')).toBe(0);
+	});
+});
+
+describe('clusterIdForSubIndex', () => {
+	it('mapt subIndex auf sortierte Cluster-IDs', () => {
+		const text = '{{c3::c}} {{c1::a}} {{c2::b}}';
+		expect(clusterIdForSubIndex(text, 0)).toBe(1);
+		expect(clusterIdForSubIndex(text, 1)).toBe(2);
+		expect(clusterIdForSubIndex(text, 2)).toBe(3);
+		expect(clusterIdForSubIndex(text, 3)).toBe(null);
+	});
+});
+
+describe('renderClozePrompt', () => {
+	it('maskiert aktiven Cluster, expandiert andere', () => {
+		const out = renderClozePrompt('{{c1::A}} und {{c2::B}}', 1);
+		expect(out).toBe('[…] und B');
+	});
+
+	it('droppt Hint beim Maskieren', () => {
+		const out = renderClozePrompt('Die {{c1::Antwort::Hinweis}}.', 1);
+		expect(out).toBe('Die […].');
+	});
+});
+
+describe('renderClozeAnswer', () => {
+	it('expandiert alle Cluster, markiert aktiven mit Bold', () => {
+		const out = renderClozeAnswer('{{c1::A}} und {{c2::B}}', 1);
+		expect(out).toBe('**A** und B');
+	});
+});
diff --git a/packages/cards-domain/tests/fsrs.test.ts b/packages/cards-domain/tests/fsrs.test.ts
index 43cb783..cdd35c2 100644
--- a/packages/cards-domain/tests/fsrs.test.ts
+++ b/packages/cards-domain/tests/fsrs.test.ts
@@ -81,6 +81,10 @@ describe('subIndexCount', () => {
 	it('unknown type defaults to 1', () => {
 		expect(subIndexCount('unknown-future-type')).toBe(1);
 	});
+
+	it('cloze wirft — Caller muss subIndexCountForCloze nutzen', () => {
+		expect(() => subIndexCount('cloze')).toThrow(/subIndexCountForCloze/);
+	});
 });
 
 describe('buildScheduler', () => {
diff --git a/packages/cards-domain/tests/schemas.test.ts b/packages/cards-domain/tests/schemas.test.ts
index 9610770..f35874f 100644
--- a/packages/cards-domain/tests/schemas.test.ts
+++ b/packages/cards-domain/tests/schemas.test.ts
@@ -14,10 +14,14 @@ describe('CardTypeSchema', () => {
 	it('accepts MVP types', () => {
 		expect(() => CardTypeSchema.parse('basic')).not.toThrow();
 		expect(() => CardTypeSchema.parse('basic-reverse')).not.toThrow();
+		expect(() => CardTypeSchema.parse('cloze')).not.toThrow();
 	});
 
-	it('rejects future types in MVP schema', () => {
-		expect(() => CardTypeSchema.parse('cloze')).toThrow();
+	it('rejects future types not yet in MVP schema', () => {
+		expect(() => CardTypeSchema.parse('image-occlusion')).toThrow();
+		expect(() => CardTypeSchema.parse('type-in')).toThrow();
+		expect(() => CardTypeSchema.parse('audio')).toThrow();
+		expect(() => CardTypeSchema.parse('multiple-choice')).toThrow();
 	});
 });
 
@@ -55,11 +59,20 @@ describe('CardCreateSchema', () => {
 		expect(r.success).toBe(false);
 	});
 
-	it('rejects unknown type via CardTypeSchema', () => {
+	it('accepts a cloze card with text field', () => {
 		const r = CardCreateSchema.safeParse({
 			deck_id: 'd-1',
 			type: 'cloze',
-			fields: { text: 'x' },
+			fields: { text: '{{c1::Paris}} ist die Hauptstadt.' },
+		});
+		expect(r.success).toBe(true);
+	});
+
+	it('rejects unknown type via CardTypeSchema', () => {
+		const r = CardCreateSchema.safeParse({
+			deck_id: 'd-1',
+			type: 'image-occlusion',
+			fields: { image_ref: 'x', mask_regions: 'y' },
 		});
 		expect(r.success).toBe(false);
 	});