diff --git a/packages/api/src/__tests__/assistant-tools-metro-city-mutations-errors.test.ts b/packages/api/src/__tests__/assistant-tools-metro-city-mutations-errors.test.ts
new file mode 100644
index 0000000..c8eda36
--- /dev/null
+++ b/packages/api/src/__tests__/assistant-tools-metro-city-mutations-errors.test.ts
@@ -0,0 +1,68 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+import { executeTool } from "../router/assistant-tools.js";
+import { createToolContext } from "./assistant-tools-country-test-helpers.js";
+
+describe("assistant metro city mutation tools - errors", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("returns a stable error when creating a metro city for a missing country", async () => {
+    const ctx = createToolContext({
+      country: {
+        findUnique: vi.fn().mockResolvedValue(null),
+      },
+    });
+
+    const result = await executeTool(
+      "create_metro_city",
+      JSON.stringify({ countryId: "country_missing", name: "Munich" }),
+      ctx,
+    );
+
+    expect(JSON.parse(result.content)).toEqual({
+      error: "Country not found with the given criteria.",
+    });
+  });
+
+  it("returns a stable error when updating a missing metro city", async () => {
+    const ctx = createToolContext({
+      metroCity: {
+        findUnique: vi.fn().mockResolvedValue(null),
+      },
+    });
+
+    const result = await executeTool(
+      "update_metro_city",
+      JSON.stringify({ id: "city_missing", data: { name: "Hamburg-Mitte" } }),
+      ctx,
+    );
+
+    expect(JSON.parse(result.content)).toEqual({
+      error: "Metro city not found with the given criteria.",
+    });
+  });
+
+  it("returns a stable error when deleting a metro city that is still assigned", async () => {
+    const ctx = createToolContext({
+      metroCity: {
+        findUnique: vi.fn().mockResolvedValue({
+          id: "city_ham",
+          name: "Hamburg",
+          _count: { resources: 3 },
+        }),
+      },
+    });
+
+    const result = await executeTool(
+      "delete_metro_city",
+      JSON.stringify({ id: "city_ham" }),
+      ctx,
+    );
+
+    expect(JSON.parse(result.content)).toEqual({
+      error: "Metro city cannot be deleted while it is still assigned to resources.",
+    });
+  });
+});
diff --git a/packages/api/src/__tests__/assistant-tools-metro-city-mutations-success.test.ts b/packages/api/src/__tests__/assistant-tools-metro-city-mutations-success.test.ts
new file mode 100644
index 0000000..39eee5d
--- /dev/null
+++ b/packages/api/src/__tests__/assistant-tools-metro-city-mutations-success.test.ts
@@ -0,0 +1,117 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+import { executeTool } from "../router/assistant-tools.js";
+import { createToolContext } from "./assistant-tools-country-test-helpers.js";
+
+describe("assistant metro city mutation tools - success", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("creates, updates, and deletes metro cities for admin users", async () => {
+    const create = vi.fn().mockResolvedValue({
+      id: "city_muc",
+      name: "Munich",
+      countryId: "country_de",
+    });
+    const findUnique = vi.fn()
+      .mockResolvedValueOnce({ id: "city_muc", name: "Munich", countryId: "country_de" })
+      .mockResolvedValueOnce({ id: "city_muc", name: "Munich", _count: { resources: 0 } });
+    const update = vi.fn().mockResolvedValue({
+      id: "city_muc",
+      name: "Muenchen",
+      countryId: "country_de",
+    });
+    const remove = vi.fn().mockResolvedValue({ id: "city_muc" });
+    const ctx = createToolContext({
+      country: {
+        findUnique: vi.fn().mockResolvedValue({ id: "country_de", name: "Germany" }),
+      },
+      metroCity: {
+        create,
+        findUnique,
+        update,
+        delete: remove,
+      },
+    });
+
+    const createResult = await executeTool(
+      "create_metro_city",
+      JSON.stringify({ countryId: "country_de", name: "Munich" }),
+      ctx,
+    );
+    const updateResult = await executeTool(
+      "update_metro_city",
+      JSON.stringify({ id: "city_muc", data: { name: "Muenchen" } }),
+      ctx,
+    );
+    const deleteResult = await executeTool(
+      "delete_metro_city",
+      JSON.stringify({ id: "city_muc" }),
+      ctx,
+    );
+
+    expect(create).toHaveBeenCalledWith({
+      data: { name: "Munich", countryId: "country_de" },
+    });
+    expect(update).toHaveBeenCalledWith({
+      where: { id: "city_muc" },
+      data: { name: "Muenchen" },
+    });
+    expect(remove).toHaveBeenCalledWith({ where: { id: "city_muc" } });
+    expect(createResult.action).toEqual({
+      type: "invalidate",
+      scope: ["country", "resource", "holidayCalendar", "vacation"],
+    });
+    expect(updateResult.action).toEqual({
+      type: "invalidate",
+      scope: ["country", "resource", "holidayCalendar", "vacation"],
+    });
+    expect(deleteResult.action).toEqual({
+      type: "invalidate",
+      scope: ["country", "resource", "holidayCalendar", "vacation"],
+    });
+    expect(createResult.data).toMatchObject({
+      success: true,
+      message: "Created metro city: Munich",
+      metroCity: { id: "city_muc", name: "Munich" },
+    });
+    expect(updateResult.data).toMatchObject({
+      success: true,
+      message: "Updated metro city: Muenchen",
+      metroCity: { id: "city_muc", name: "Muenchen" },
+    });
+    expect(deleteResult.data).toMatchObject({
+      success: true,
+      message: "Deleted metro city: Munich",
+    });
+  });
+
+  it("deletes metro cities only when no resources are assigned", async () => {
+    const ctx = createToolContext({
+      metroCity: {
+        findUnique: vi.fn().mockResolvedValue({
+          id: "city_ham",
+          name: "Hamburg",
+          _count: { resources: 0 },
+        }),
+        delete: vi.fn().mockResolvedValue(undefined),
+      },
+    });
+
+    const result = await executeTool(
+      "delete_metro_city",
+      JSON.stringify({ id: "city_ham" }),
+      ctx,
+    );
+
+    expect(result.action).toEqual({
+      type: "invalidate",
+      scope: ["country", "resource", "holidayCalendar", "vacation"],
+    });
+    expect(result.data).toMatchObject({
+      success: true,
+      message: "Deleted metro city: Hamburg",
+    });
+  });
+});