diff --git a/packages/api/src/__tests__/assistant-tools-vacation-create.test.ts b/packages/api/src/__tests__/assistant-tools-vacation-create.test.ts
new file mode 100644
index 0000000..a22c895
--- /dev/null
+++ b/packages/api/src/__tests__/assistant-tools-vacation-create.test.ts
@@ -0,0 +1,84 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { VacationType } from "@capakraken/db";
+import { SystemRole } from "@capakraken/shared";
+
+vi.mock("@capakraken/application", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@capakraken/application")>();
+  return {
+    ...actual,
+    approveEstimateVersion: vi.fn(),
+    cloneEstimate: vi.fn(),
+    commitDispoImportBatch: vi.fn(),
+    countPlanningEntries: vi.fn().mockResolvedValue({ countsByRoleId: new Map() }),
+    createEstimateExport: vi.fn(),
+    createEstimatePlanningHandoff: vi.fn(),
+    createEstimateRevision: vi.fn(),
+    assessDispoImportReadiness: vi.fn(),
+    loadResourceDailyAvailabilityContexts: vi.fn().mockResolvedValue(new Map()),
+    getDashboardDemand: vi.fn().mockResolvedValue([]),
+    getDashboardBudgetForecast: vi.fn().mockResolvedValue([]),
+    getDashboardOverview: vi.fn(),
+    getDashboardSkillGapSummary: vi.fn().mockResolvedValue({
+      roleGaps: [],
+      totalOpenPositions: 0,
+      skillSupplyTop10: [],
+      resourcesByRole: [],
+    }),
+    getDashboardProjectHealth: vi.fn().mockResolvedValue([]),
+    getDashboardPeakTimes: vi.fn().mockResolvedValue([]),
+    getDashboardTopValueResources: vi.fn().mockResolvedValue([]),
+    getEstimateById: vi.fn(),
+    listAssignmentBookings: vi.fn().mockResolvedValue([]),
+    stageDispoImportBatch: vi.fn(),
+    submitEstimateVersion: vi.fn(),
+    updateEstimateDraft: vi.fn(),
+  };
+});
+
+import {
+  createHappyPathDb,
+  createToolContext,
+  executeTool,
+} from "./assistant-tools-vacation-mutation-test-helpers.js";
+
+describe("assistant vacation mutation tools", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("creates vacation through the real vacation router path", async () => {
+    const db = createHappyPathDb();
+    const ctx = createToolContext(db, { userRole: SystemRole.ADMIN });
+
+    const result = await executeTool(
+      "create_vacation",
+      JSON.stringify({
+        resourceId: "res_1",
+        type: "ANNUAL",
+        startDate: "2026-07-01",
+        endDate: "2026-07-02",
+      }),
+      ctx,
+    );
+
+    expect(JSON.parse(result.content)).toEqual(
+      expect.objectContaining({
+        success: true,
+        vacationId: "vac_created",
+        message:
+          "Created ANNUAL for Alice Example: 2026-07-01 to 2026-07-02 (status: APPROVED, deducted 2 day(s))",
+      }),
+    );
+    expect(db.vacation.create).toHaveBeenCalledWith(
+      expect.objectContaining({
+        data: expect.objectContaining({
+          resourceId: "res_1",
+          type: VacationType.ANNUAL,
+          status: "APPROVED",
+          requestedById: "user_1",
+          approvedById: "user_1",
+        }),
+      }),
+    );
+  });
+});
diff --git a/packages/api/src/__tests__/assistant-tools-vacation-creation-errors.test.ts b/packages/api/src/__tests__/assistant-tools-vacation-creation-errors.test.ts
new file mode 100644
index 0000000..a8ff682
--- /dev/null
+++ b/packages/api/src/__tests__/assistant-tools-vacation-creation-errors.test.ts
@@ -0,0 +1,164 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { SystemRole } from "@capakraken/shared";
+
+vi.mock("@capakraken/application", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@capakraken/application")>();
+  return {
+    ...actual,
+    approveEstimateVersion: vi.fn(),
+    cloneEstimate: vi.fn(),
+    commitDispoImportBatch: vi.fn(),
+    countPlanningEntries: vi.fn().mockResolvedValue({ countsByRoleId: new Map() }),
+    createEstimateExport: vi.fn(),
+    createEstimatePlanningHandoff: vi.fn(),
+    createEstimateRevision: vi.fn(),
+    assessDispoImportReadiness: vi.fn(),
+    loadResourceDailyAvailabilityContexts: vi.fn().mockResolvedValue(new Map()),
+    getDashboardDemand: vi.fn().mockResolvedValue([]),
+    getDashboardBudgetForecast: vi.fn().mockResolvedValue([]),
+    getDashboardOverview: vi.fn(),
+    getDashboardSkillGapSummary: vi.fn().mockResolvedValue({
+      roleGaps: [],
+      totalOpenPositions: 0,
+      skillSupplyTop10: [],
+      resourcesByRole: [],
+    }),
+    getDashboardProjectHealth: vi.fn().mockResolvedValue([]),
+    getDashboardPeakTimes: vi.fn().mockResolvedValue([]),
+    getDashboardTopValueResources: vi.fn().mockResolvedValue([]),
+    getEstimateById: vi.fn(),
+    listAssignmentBookings: vi.fn().mockResolvedValue([]),
+    stageDispoImportBatch: vi.fn(),
+    submitEstimateVersion: vi.fn(),
+    updateEstimateDraft: vi.fn(),
+  };
+});
+
+import { executeTool } from "../router/assistant-tools.js";
+import { createToolContext } from "./assistant-tools-vacation-entitlement-test-helpers.js";
+
+describe("assistant vacation creation error paths", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("returns a stable assistant error when vacation creation receives an invalid end date", async () => {
+    const ctx = createToolContext(
+      {
+        resource: {
+          findUnique: vi.fn()
+            .mockResolvedValueOnce(null)
+            .mockResolvedValueOnce({
+              id: "res_1",
+              eid: "EMP-001",
+              displayName: "Alice Example",
+              chapter: "Delivery",
+            }),
+          findFirst: vi.fn().mockResolvedValue(null),
+        },
+      },
+      { userRole: SystemRole.ADMIN },
+    );
+
+    const result = await executeTool(
+      "create_vacation",
+      JSON.stringify({
+        resourceId: "EMP-001",
+        type: "ANNUAL",
+        startDate: "2026-09-07",
+        endDate: "2026-09-99",
+      }),
+      ctx,
+    );
+
+    expect(JSON.parse(result.content)).toEqual({
+      error: "Invalid endDate: 2026-09-99",
+    });
+  });
+
+  it("returns a stable assistant error when vacation creation overlaps an existing request", async () => {
+    const ctx = createToolContext(
+      {
+        resource: {
+          findUnique: vi.fn()
+            .mockResolvedValueOnce(null)
+            .mockResolvedValueOnce({
+              id: "res_1",
+              eid: "EMP-001",
+              displayName: "Alice Example",
+              chapter: "Delivery",
+            }),
+          findFirst: vi.fn().mockResolvedValue(null),
+        },
+        user: {
+          findUnique: vi.fn().mockResolvedValue({ id: "user_1", systemRole: "MANAGER" }),
+        },
+        vacation: {
+          findFirst: vi.fn().mockResolvedValue({
+            id: "vac_existing",
+            resourceId: "res_1",
+          }),
+        },
+      },
+      { userRole: SystemRole.MANAGER },
+    );
+
+    const result = await executeTool(
+      "create_vacation",
+      JSON.stringify({
+        resourceId: "EMP-001",
+        type: "ANNUAL",
+        startDate: "2026-09-07",
+        endDate: "2026-09-09",
+      }),
+      ctx,
+    );
+
+    expect(JSON.parse(result.content)).toEqual({
+      error: "Overlapping vacation already exists for this resource in the selected period",
+    });
+  });
+
+  it("returns a stable assistant error when a user tries to create vacation for another resource", async () => {
+    const ctx = createToolContext(
+      {
+        resource: {
+          findUnique: vi.fn()
+            .mockResolvedValueOnce(null)
+            .mockResolvedValueOnce({
+              id: "res_1",
+              eid: "EMP-001",
+              displayName: "Alice Example",
+              chapter: "Delivery",
+              isActive: true,
+            })
+            .mockResolvedValueOnce({
+              userId: "user_2",
+            }),
+          findFirst: vi.fn().mockResolvedValue({
+            id: "res_1",
+          }),
+        },
+        user: {
+          findUnique: vi.fn().mockResolvedValue({ id: "user_1", systemRole: "USER" }),
+        },
+      },
+      { userRole: SystemRole.USER },
+    );
+
+    const result = await executeTool(
+      "create_vacation",
+      JSON.stringify({
+        resourceId: "EMP-001",
+        type: "ANNUAL",
+        startDate: "2026-09-07",
+        endDate: "2026-09-09",
+      }),
+      ctx,
+    );
+
+    expect(JSON.parse(result.content)).toEqual({
+      error: "You can only create vacation requests for your own resource.",
+    });
+  });
+});
diff --git a/packages/api/src/__tests__/assistant-tools-vacation-mutation-test-helpers.ts b/packages/api/src/__tests__/assistant-tools-vacation-mutation-test-helpers.ts
new file mode 100644
index 0000000..fa70025
--- /dev/null
+++ b/packages/api/src/__tests__/assistant-tools-vacation-mutation-test-helpers.ts
@@ -0,0 +1,164 @@
+import { VacationType } from "@capakraken/db";
+import { vi } from "vitest";
+
+import {
+  executeTool as executeAssistantTool,
+} from "../router/assistant-tools.js";
+
+export { createToolContext } from "./assistant-tools-vacation-entitlement-test-helpers.js";
+
+export function createHappyPathDb() {
+  const vacationFindUnique = vi.fn().mockImplementation(async (args?: any) => {
+    const id = args?.where?.id;
+    if (id === "vac_cancelled") {
+      return {
+        id,
+        resourceId: "res_1",
+        requestedById: "user_1",
+        status: "CANCELLED",
+        startDate: new Date("2026-07-01T00:00:00.000Z"),
+        endDate: new Date("2026-07-02T00:00:00.000Z"),
+        type: VacationType.ANNUAL,
+        isHalfDay: false,
+        resource: {
+          id: "res_1",
+          displayName: "Alice Example",
+          eid: "EMP-001",
+          chapter: "Delivery",
+        },
+        requestedBy: { id: "user_1", name: "Assistant User", email: "assistant@example.com" },
+        approvedBy: null,
+      };
+    }
+    if (id === "vac_pending") {
+      return {
+        id,
+        resourceId: "res_1",
+        requestedById: "user_1",
+        status: "PENDING",
+        startDate: new Date("2026-08-03T00:00:00.000Z"),
+        endDate: new Date("2026-08-04T00:00:00.000Z"),
+        type: VacationType.ANNUAL,
+        isHalfDay: false,
+        resource: {
+          id: "res_1",
+          displayName: "Alice Example",
+          eid: "EMP-001",
+          chapter: "Delivery",
+        },
+        requestedBy: { id: "user_1", name: "Assistant User", email: "assistant@example.com" },
+        approvedBy: null,
+      };
+    }
+    if (id === "vac_self") {
+      return {
+        id,
+        resourceId: "res_1",
+        requestedById: "user_1",
+        status: "APPROVED",
+        startDate: new Date("2026-09-07T00:00:00.000Z"),
+        endDate: new Date("2026-09-09T00:00:00.000Z"),
+        resource: {
+          id: "res_1",
+          displayName: "Alice Example",
+          eid: "EMP-001",
+          chapter: "Delivery",
+        },
+        requestedBy: { id: "user_1", name: "Assistant User", email: "assistant@example.com" },
+        approvedBy: null,
+      };
+    }
+    return null;
+  });
+
+  return {
+    user: {
+      findUnique: vi.fn().mockResolvedValue({ id: "user_1", systemRole: "MANAGER" }),
+    },
+    resource: {
+      findUnique: vi.fn().mockImplementation(async (args?: any) => {
+        if (args?.where?.id === "res_1") {
+          return {
+            id: "res_1",
+            eid: "EMP-001",
+            displayName: "Alice Example",
+            userId: "user_1",
+            chapter: "Delivery",
+            federalState: "BY",
+            countryId: "country_de",
+            metroCityId: null,
+            country: { code: "DE", name: "Germany" },
+            metroCity: null,
+          };
+        }
+        return { userId: "user_1" };
+      }),
+      count: vi.fn().mockResolvedValue(1),
+      findFirst: vi.fn().mockResolvedValue(null),
+    },
+    holidayCalendar: {
+      findMany: vi.fn().mockResolvedValue([]),
+    },
+    systemSettings: {
+      findUnique: vi.fn()
+        .mockResolvedValueOnce({ vacationDefaultDays: 30 })
+        .mockResolvedValueOnce({ anonymizationEnabled: false }),
+    },
+    vacationEntitlement: {
+      findUnique: vi.fn().mockResolvedValue(null),
+      create: vi.fn(),
+      update: vi.fn(),
+    },
+    vacation: {
+      findUnique: vacationFindUnique,
+      findMany: vi.fn().mockResolvedValue([]),
+      findFirst: vi.fn().mockResolvedValue(null),
+      create: vi.fn().mockResolvedValue({
+        id: "vac_created",
+        resourceId: "res_1",
+        status: "APPROVED",
+        type: VacationType.ANNUAL,
+        startDate: new Date("2026-07-01T00:00:00.000Z"),
+        endDate: new Date("2026-07-02T00:00:00.000Z"),
+        isHalfDay: false,
+        resource: {
+          id: "res_1",
+          displayName: "Alice Example",
+          eid: "EMP-001",
+          chapter: "Delivery",
+        },
+        requestedBy: { id: "user_1", name: "Assistant User", email: "assistant@example.com" },
+        effectiveDays: 2,
+      }),
+      update: vi.fn().mockImplementation(async (args?: any) => {
+        const existing = await vacationFindUnique({ where: { id: args?.where?.id } });
+        return {
+          ...(existing ?? {
+            id: args?.where?.id ?? "vac_unknown",
+            resourceId: "res_1",
+            startDate: new Date("2026-07-01T00:00:00.000Z"),
+            endDate: new Date("2026-07-02T00:00:00.000Z"),
+            type: VacationType.ANNUAL,
+            isHalfDay: false,
+          }),
+          status: args?.data?.status ?? existing?.status ?? "APPROVED",
+          rejectionReason: args?.data?.rejectionReason ?? null,
+          approvedAt: args?.data?.approvedAt ?? null,
+          approvedById: args?.data?.approvedById ?? existing?.approvedById ?? null,
+        };
+      }),
+    },
+    notification: {
+      updateMany: vi.fn().mockResolvedValue({ count: 1 }),
+      create: vi.fn().mockResolvedValue({ id: "note_1", userId: "user_1" }),
+    },
+    auditLog: {
+      create: vi.fn().mockResolvedValue({ id: "audit_1" }),
+    },
+    webhook: {
+      findMany: vi.fn().mockResolvedValue([]),
+    },
+  };
+}
+
+export const executeTool = executeAssistantTool;
diff --git a/packages/api/src/__tests__/assistant-tools-vacation-review-cancel.test.ts b/packages/api/src/__tests__/assistant-tools-vacation-review-cancel.test.ts
new file mode 100644
index 0000000..285fc5f
--- /dev/null
+++ b/packages/api/src/__tests__/assistant-tools-vacation-review-cancel.test.ts
@@ -0,0 +1,110 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { SystemRole } from "@capakraken/shared";
+
+vi.mock("@capakraken/application", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@capakraken/application")>();
+  return {
+    ...actual,
+    approveEstimateVersion: vi.fn(),
+    cloneEstimate: vi.fn(),
+    commitDispoImportBatch: vi.fn(),
+    countPlanningEntries: vi.fn().mockResolvedValue({ countsByRoleId: new Map() }),
+    createEstimateExport: vi.fn(),
+    createEstimatePlanningHandoff: vi.fn(),
+    createEstimateRevision: vi.fn(),
+    assessDispoImportReadiness: vi.fn(),
+    loadResourceDailyAvailabilityContexts: vi.fn().mockResolvedValue(new Map()),
+    getDashboardDemand: vi.fn().mockResolvedValue([]),
+    getDashboardBudgetForecast: vi.fn().mockResolvedValue([]),
+    getDashboardOverview: vi.fn(),
+    getDashboardSkillGapSummary: vi.fn().mockResolvedValue({
+      roleGaps: [],
+      totalOpenPositions: 0,
+      skillSupplyTop10: [],
+      resourcesByRole: [],
+    }),
+    getDashboardProjectHealth: vi.fn().mockResolvedValue([]),
+    getDashboardPeakTimes: vi.fn().mockResolvedValue([]),
+    getDashboardTopValueResources: vi.fn().mockResolvedValue([]),
+    getEstimateById: vi.fn(),
+    listAssignmentBookings: vi.fn().mockResolvedValue([]),
+    stageDispoImportBatch: vi.fn(),
+    submitEstimateVersion: vi.fn(),
+    updateEstimateDraft: vi.fn(),
+  };
+});
+
+import {
+  createHappyPathDb,
+  createToolContext,
+  executeTool,
+} from "./assistant-tools-vacation-mutation-test-helpers.js";
+
+describe("assistant vacation mutation tools", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("approves and rejects vacation through the real vacation router path", async () => {
+    const db = createHappyPathDb();
+    const ctx = createToolContext(db, { userRole: SystemRole.ADMIN });
+
+    const approveResult = await executeTool(
+      "approve_vacation",
+      JSON.stringify({ vacationId: "vac_cancelled" }),
+      ctx,
+    );
+    const rejectResult = await executeTool(
+      "reject_vacation",
+      JSON.stringify({ vacationId: "vac_pending", reason: "Capacity freeze" }),
+      ctx,
+    );
+
+    expect(JSON.parse(approveResult.content)).toEqual(
+      expect.objectContaining({
+        success: true,
+        message: "Approved vacation for Alice Example",
+      }),
+    );
+    expect(JSON.parse(rejectResult.content)).toEqual(
+      expect.objectContaining({
+        success: true,
+        message: "Rejected vacation for Alice Example: Capacity freeze",
+      }),
+    );
+    expect(db.vacation.update).toHaveBeenCalledWith(
+      expect.objectContaining({
+        where: { id: "vac_cancelled" },
+        data: expect.objectContaining({ status: "APPROVED" }),
+      }),
+    );
+    expect(db.vacation.update).toHaveBeenCalledWith(
+      expect.objectContaining({
+        where: { id: "vac_pending" },
+        data: expect.objectContaining({ status: "REJECTED", rejectionReason: "Capacity freeze" }),
+      }),
+    );
+  });
+
+  it("allows self-service vacation cancellation through the real vacation router path", async () => {
+    const db = createHappyPathDb();
+    const ctx = createToolContext(db, { userRole: SystemRole.USER, permissions: [] });
+
+    const result = await executeTool(
+      "cancel_vacation",
+      JSON.stringify({ vacationId: "vac_self" }),
+      ctx,
+    );
+
+    expect(JSON.parse(result.content)).toEqual(
+      expect.objectContaining({
+        success: true,
+        message: "Cancelled vacation for Alice Example",
+      }),
+    );
+    expect(db.vacation.update).toHaveBeenCalledWith({
+      where: { id: "vac_self" },
+      data: { status: "CANCELLED" },
+    });
+  });
+});