diff --git a/frontend/src/lib/planner/reasoningTags.test.ts b/frontend/src/lib/planner/reasoningTags.test.ts
new file mode 100644
index 0000000..9099f96
--- /dev/null
+++ b/frontend/src/lib/planner/reasoningTags.test.ts
@@ -0,0 +1,106 @@
+import { describe, it, expect } from 'vitest';
+import { computeReasoningTags, type ReasoningTag } from './reasoningTags';
+
+// SlotMap fixture helpers
+const emptySlotMap = {};
+
+const slotMapWithChicken = {
+	'2026-04-07': { id: 's1', slotDate: '2026-04-07', recipe: { id: 'r1', name: 'Chicken curry', tags: [{ id: 't1', name: 'Hähnchen', tagType: 'protein' }] } },
+};
+
+const slotMapWithBeefAndChicken = {
+	'2026-04-07': { id: 's1', slotDate: '2026-04-07', recipe: { id: 'r1', name: 'Steak', tags: [{ id: 't2', name: 'Rind', tagType: 'protein' }] } },
+	'2026-04-08': { id: 's2', slotDate: '2026-04-08', recipe: { id: 'r2', name: 'Chicken', tags: [{ id: 't1', name: 'Hähnchen', tagType: 'protein' }] } },
+};
+
+const fishRecipe = { id: 'r3', name: 'Lachs', cookTimeMin: 20, effort: 'einfach', tags: [{ id: 't3', name: 'Fisch', tagType: 'protein' }] };
+const chickenRecipe = { id: 'r1', name: 'Chicken curry', cookTimeMin: 45, effort: 'mittel', tags: [{ id: 't1', name: 'Hähnchen', tagType: 'protein' }] };
+const easyRecipe = { id: 'r4', name: 'Salat', cookTimeMin: 15, effort: 'einfach', tags: [] };
+const heavyRecipe = { id: 'r5', name: 'Roulade', cookTimeMin: 90, effort: 'aufwändig', tags: [] };
+
+describe('computeReasoningTags', () => {
+	describe('Neues Protein tag', () => {
+		it('returns Neues Protein tag when recipe protein is not in week', () => {
+			const tags = computeReasoningTags(slotMapWithChicken, fishRecipe);
+			const tagTypes = tags.map((t: ReasoningTag) => t.id);
+			expect(tagTypes).toContain('neues-protein');
+		});
+
+		it('does not return Neues Protein when recipe protein is already in week', () => {
+			const tags = computeReasoningTags(slotMapWithChicken, chickenRecipe);
+			const tagTypes = tags.map((t: ReasoningTag) => t.id);
+			expect(tagTypes).not.toContain('neues-protein');
+		});
+
+		it('returns Neues Protein when recipe has protein tag and slotMap is empty', () => {
+			const tags = computeReasoningTags(emptySlotMap, fishRecipe);
+			const tagTypes = tags.map((t: ReasoningTag) => t.id);
+			expect(tagTypes).toContain('neues-protein');
+		});
+
+		it('does not return Neues Protein when recipe has no protein tag', () => {
+			const tags = computeReasoningTags(emptySlotMap, easyRecipe);
+			const tagTypes = tags.map((t: ReasoningTag) => t.id);
+			expect(tagTypes).not.toContain('neues-protein');
+		});
+	});
+
+	describe('Aufwand: leicht tag', () => {
+		it('returns Aufwand tag when cookTimeMin is less than 30', () => {
+			const tags = computeReasoningTags(emptySlotMap, easyRecipe);
+			const tagTypes = tags.map((t: ReasoningTag) => t.id);
+			expect(tagTypes).toContain('aufwand-leicht');
+		});
+
+		it('returns Aufwand tag when effort is einfach regardless of cookTime', () => {
+			const recipe = { ...fishRecipe, cookTimeMin: 45 };
+			const tags = computeReasoningTags(emptySlotMap, recipe);
+			const tagTypes = tags.map((t: ReasoningTag) => t.id);
+			expect(tagTypes).toContain('aufwand-leicht');
+		});
+
+		it('does not return Aufwand tag for heavy recipe', () => {
+			const tags = computeReasoningTags(emptySlotMap, heavyRecipe);
+			const tagTypes = tags.map((t: ReasoningTag) => t.id);
+			expect(tagTypes).not.toContain('aufwand-leicht');
+		});
+
+		it('returns Aufwand tag exactly at cookTimeMin 29', () => {
+			const recipe = { ...heavyRecipe, cookTimeMin: 29, effort: undefined };
+			const tags = computeReasoningTags(emptySlotMap, recipe);
+			expect(tags.map((t: ReasoningTag) => t.id)).toContain('aufwand-leicht');
+		});
+
+		it('does not return Aufwand tag at cookTimeMin 30 with non-easy effort', () => {
+			const recipe = { ...heavyRecipe, cookTimeMin: 30, effort: 'mittel' };
+			const tags = computeReasoningTags(emptySlotMap, recipe);
+			expect(tags.map((t: ReasoningTag) => t.id)).not.toContain('aufwand-leicht');
+		});
+	});
+
+	describe('ReasoningTag shape', () => {
+		it('each tag has id, label, and color', () => {
+			const tags = computeReasoningTags(emptySlotMap, fishRecipe);
+			for (const tag of tags) {
+				expect(tag).toHaveProperty('id');
+				expect(tag).toHaveProperty('label');
+				expect(tag).toHaveProperty('color');
+			}
+		});
+	});
+
+	describe('multiple tags', () => {
+		it('returns multiple tags when multiple conditions are true', () => {
+			const recipe = { id: 'r6', name: 'Easy fish', cookTimeMin: 20, effort: 'einfach', tags: [{ id: 't3', name: 'Fisch', tagType: 'protein' }] };
+			const tags = computeReasoningTags(slotMapWithBeefAndChicken, recipe);
+			const tagIds = tags.map((t: ReasoningTag) => t.id);
+			expect(tagIds).toContain('neues-protein');
+			expect(tagIds).toContain('aufwand-leicht');
+		});
+
+		it('returns empty array when no conditions are true', () => {
+			const tags = computeReasoningTags(slotMapWithChicken, { ...chickenRecipe, cookTimeMin: 60, effort: 'aufwändig' });
+			expect(tags).toHaveLength(0);
+		});
+	});
+});
diff --git a/frontend/src/lib/planner/reasoningTags.ts b/frontend/src/lib/planner/reasoningTags.ts
new file mode 100644
index 0000000..e0a5c09
--- /dev/null
+++ b/frontend/src/lib/planner/reasoningTags.ts
@@ -0,0 +1,63 @@
+export interface ReasoningTag {
+	id: 'neues-protein' | 'aufwand-leicht';
+	label: string;
+	color: 'green' | 'yellow';
+}
+
+interface TagItem {
+	id?: string;
+	name?: string;
+	tagType?: string;
+}
+
+interface Recipe {
+	id: string;
+	name: string;
+	cookTimeMin?: number;
+	effort?: string;
+	tags?: TagItem[];
+}
+
+interface SlotRecipe {
+	id?: string;
+	tags?: TagItem[];
+}
+
+interface Slot {
+	id?: string;
+	slotDate?: string;
+	recipe?: SlotRecipe | null;
+}
+
+type SlotMap = Record<string, Slot>;
+
+export function computeReasoningTags(slotMap: SlotMap, recipe: Recipe): ReasoningTag[] {
+	const tags: ReasoningTag[] = [];
+
+	// Neues Protein: recipe has a protein tag not already present in any filled slot
+	const recipeProtein = recipe.tags?.find((t) => t.tagType === 'protein')?.name;
+	if (recipeProtein) {
+		const weekProteins = new Set<string>();
+		for (const slot of Object.values(slotMap)) {
+			if (slot.recipe) {
+				for (const tag of slot.recipe.tags ?? []) {
+					if (tag.tagType === 'protein' && tag.name) {
+						weekProteins.add(tag.name);
+					}
+				}
+			}
+		}
+		if (!weekProteins.has(recipeProtein)) {
+			tags.push({ id: 'neues-protein', label: 'Neues Protein', color: 'green' });
+		}
+	}
+
+	// Aufwand: leicht — cookTimeMin < 30 OR effort is 'einfach'/'leicht'
+	const isEasyEffort = recipe.effort === 'einfach' || recipe.effort === 'leicht';
+	const isQuick = recipe.cookTimeMin != null && recipe.cookTimeMin < 30;
+	if (isEasyEffort || isQuick) {
+		tags.push({ id: 'aufwand-leicht', label: 'Aufwand: leicht', color: 'yellow' });
+	}
+
+	return tags;
+}