diff --git a/src/app/api/plugins/execute/route.js b/src/app/api/plugins/execute/route.js
index 5ebc773..ef05061 100644
--- a/src/app/api/plugins/execute/route.js
+++ b/src/app/api/plugins/execute/route.js
@@ -15,7 +15,14 @@ export async function POST(request, { params } = {}) {
       return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
     }
 
-    const { message, context = {} } = await request.json();
+    let body;
+    try {
+      body = await request.json();
+    } catch {
+      return NextResponse.json({ error: 'Invalid JSON body' }, { status: 400 });
+    }
+
+    const { message, context = {} } = body;
 
     if (!message) {
       return NextResponse.json({ error: 'Message is required' }, { status: 400 });
diff --git a/src/app/api/plugins/execute/route.test.js b/src/app/api/plugins/execute/route.test.js
new file mode 100644
index 0000000..c911c47
--- /dev/null
+++ b/src/app/api/plugins/execute/route.test.js
@@ -0,0 +1,48 @@
+import { describe, expect, it, vi } from 'vitest';
+
+const mocks = vi.hoisted(() => ({
+	mockGetUser: vi.fn(),
+	mockInitialize: vi.fn(),
+	mockProcessCommand: vi.fn(),
+	mockGetAvailableCommands: vi.fn(),
+	mockGetHelpText: vi.fn()
+}));
+
+vi.mock('@/lib/supabase.js', () => ({
+	createSupabaseServerClient: vi.fn(() => ({
+		auth: {
+			getUser: mocks.mockGetUser
+		}
+	}))
+}));
+
+vi.mock('@/lib/plugins/PluginManager.js', () => ({
+	pluginManager: {
+		initialized: false,
+		initialize: mocks.mockInitialize,
+		processCommand: mocks.mockProcessCommand,
+		getAvailableCommands: mocks.mockGetAvailableCommands,
+		getHelpText: mocks.mockGetHelpText,
+		plugins: new Map()
+	}
+}));
+
+describe('POST /api/plugins/execute validation', () => {
+	it('returns 400 for malformed JSON instead of a generic 500', async () => {
+		mocks.mockGetUser.mockResolvedValue({
+			data: { user: { id: 'auth-user-id' } },
+			error: null
+		});
+
+		const { POST } = await import('./route.js');
+		const response = await POST({
+			json: vi.fn().mockRejectedValue(new SyntaxError('Unexpected token'))
+		});
+		const body = await response.json();
+
+		expect(response.status).toBe(400);
+		expect(body.error).toBe('Invalid JSON body');
+		expect(mocks.mockInitialize).not.toHaveBeenCalled();
+		expect(mocks.mockProcessCommand).not.toHaveBeenCalled();
+	});
+});