diff --git a/tests/api/hardcover-shelves-id.routes.test.ts b/tests/api/hardcover-shelves-id.routes.test.ts
index 7d084ea..dc10efe 100644
--- a/tests/api/hardcover-shelves-id.routes.test.ts
+++ b/tests/api/hardcover-shelves-id.routes.test.ts
@@ -164,6 +164,40 @@ describe('PATCH /api/user/hardcover-shelves/[id]', () => {
     expect(jobQueueMock.addSyncShelvesJob).not.toHaveBeenCalled();
   });
 
+  it('triggers a sync when forceSync is true, even if no fields changed', async () => {
+    prismaMock.hardcoverShelf.findUnique.mockResolvedValueOnce(SHELF);
+    prismaMock.hardcoverShelf.update.mockResolvedValueOnce(SHELF);
+
+    const { PATCH } =
+      await import('@/app/api/user/hardcover-shelves/[id]/route');
+    const response = await PATCH(
+      {
+        json: vi
+          .fn()
+          .mockResolvedValue({ listId: SHELF.listId, forceSync: true }),
+      } as any,
+      { params: Promise.resolve({ id: 'hc-shelf-1' }) },
+    );
+    const payload = await response.json();
+
+    expect(response.status).toBe(200);
+    expect(payload.success).toBe(true);
+    expect(prismaMock.hardcoverShelf.update).toHaveBeenCalledWith({
+      where: { id: 'hc-shelf-1' },
+      data: expect.objectContaining({
+        lastSyncAt: null,
+        bookCount: null,
+        coverUrls: null,
+      }),
+    });
+    expect(jobQueueMock.addSyncShelvesJob).toHaveBeenCalledWith(
+      undefined,
+      SHELF.id,
+      'hardcover',
+      0,
+    );
+  });
+
   it('updates listId, clears metadata, and triggers a sync job', async () => {
     prismaMock.hardcoverShelf.findUnique.mockResolvedValueOnce(SHELF);
     const updated = { ...SHELF, listId: 'status-3', lastSyncAt: null };
diff --git a/tests/api/shelves-sync.routes.test.ts b/tests/api/shelves-sync.routes.test.ts
new file mode 100644
index 0000000..1a2ada7
--- /dev/null
+++ b/tests/api/shelves-sync.routes.test.ts
@@ -0,0 +1,96 @@
+/**
+ * Component: Shelves Sync API Route Tests
+ * Documentation: documentation/backend/services/goodreads-sync.md
+ */
+
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+let authRequest: any;
+
+const requireAuthMock = vi.hoisted(() => vi.fn());
+const jobQueueMock = vi.hoisted(() => ({
+  addSyncShelvesJob: vi.fn(() => Promise.resolve()),
+}));
+
+vi.mock('@/lib/middleware/auth', () => ({
+  requireAuth: requireAuthMock,
+}));
+
+vi.mock('@/lib/services/job-queue.service', () => ({
+  getJobQueueService: () => jobQueueMock,
+}));
+
+describe('POST /api/user/shelves/sync', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    authRequest = { user: { id: 'user-1', role: 'user' } };
+    requireAuthMock.mockImplementation((_req: any, handler: any) => handler(authRequest));
+  });
+
+  it('triggers a manual sync for all shelves when no parameters provided', async () => {
+    const { POST } = await import('@/app/api/user/shelves/sync/route');
+    const response = await POST(
+      { json: vi.fn().mockResolvedValue({}) } as any,
+    );
+    const payload = await response.json();
+
+    expect(response.status).toBe(200);
+    expect(payload.success).toBe(true);
+    expect(jobQueueMock.addSyncShelvesJob).toHaveBeenCalledWith(
+      undefined, // scheduledJobId
+      undefined, // shelfId
+      undefined, // shelfType
+      0, // maxLookupsPerShelf (unlimited for manual)
+      'user-1' // userId
+    );
+  });
+
+  it('triggers a manual sync for a specific shelf', async () => {
+    const { POST } = await import('@/app/api/user/shelves/sync/route');
+    const response = await POST(
+      { json: vi.fn().mockResolvedValue({ shelfId: 'shelf-123', shelfType: 'goodreads' }) } as any,
+    );
+    const payload = await response.json();
+
+    expect(response.status).toBe(200);
+    expect(payload.success).toBe(true);
+    expect(jobQueueMock.addSyncShelvesJob).toHaveBeenCalledWith(
+      undefined, // scheduledJobId
+      'shelf-123', // shelfId
+      'goodreads', // shelfType
+      0, // maxLookupsPerShelf
+      'user-1' // userId
+    );
+  });
+
+  it('handles invalid body gracefully', async () => {
+    const { POST } = await import('@/app/api/user/shelves/sync/route');
+    const response = await POST(
+      { json: vi.fn().mockRejectedValue(new Error('Invalid JSON')) } as any,
+    );
+    const payload = await response.json();
+
+    expect(response.status).toBe(200);
+    expect(payload.success).toBe(true);
+    // Since body parsing fails gracefully with catching () => ({}), it treats it as sync all
+    expect(jobQueueMock.addSyncShelvesJob).toHaveBeenCalledWith(
+      undefined,
+      undefined,
+      undefined,
+      0,
+      'user-1'
+    );
+  });
+
+  it('validates wrong shelfType', async () => {
+    const { POST } = await import('@/app/api/user/shelves/sync/route');
+    const response = await POST(
+      { json: vi.fn().mockResolvedValue({ shelfType: 'invalid-type' }) } as any,
+    );
+    const payload = await response.json();
+
+    expect(response.status).toBe(400);
+    expect(payload.error).toBe('ValidationError');
+    expect(jobQueueMock.addSyncShelvesJob).not.toHaveBeenCalled();
+  });
+});