diff --git a/client/src/App.tsx b/client/src/App.tsx
index 6c9ae333..00fa6f46 100644
--- a/client/src/App.tsx
+++ b/client/src/App.tsx
@@ -162,14 +162,8 @@ const App = () => {
       return migrateFromLegacyAuth(legacyToken, legacyHeaderName);
     }
 
-    // Default to Authorization: Bearer as the most common case
-    return [
-      {
-        name: "Authorization",
-        value: "Bearer ",
-        enabled: true,
-      },
-    ];
+    // Default to empty array
+    return [];
   });
 
   const [pendingSampleRequests, setPendingSampleRequests] = useState<
diff --git a/client/src/lib/hooks/__tests__/useConnection.test.tsx b/client/src/lib/hooks/__tests__/useConnection.test.tsx
index 4946cdda..8d8a1f8b 100644
--- a/client/src/lib/hooks/__tests__/useConnection.test.tsx
+++ b/client/src/lib/hooks/__tests__/useConnection.test.tsx
@@ -97,9 +97,10 @@ jest.mock("@modelcontextprotocol/sdk/client/auth.js", () => ({
 }));
 
 // Mock the toast hook
+const mockToast = jest.fn();
 jest.mock("@/lib/hooks/useToast", () => ({
   useToast: () => ({
-    toast: jest.fn(),
+    toast: mockToast,
   }),
 }));
 
@@ -940,6 +941,13 @@ describe("useConnection", () => {
       expect(headers).toHaveProperty("Authorization", "Bearer mock-token");
       // Should not have the x-custom-auth-headers since Authorization is standard
       expect(headers).not.toHaveProperty("x-custom-auth-headers");
+
+      // Should show toast notification for empty Authorization header
+      expect(mockToast).toHaveBeenCalledWith({
+        title: "Invalid Authorization Header",
+        description: expect.any(String),
+        variant: "destructive",
+      });
     });
 
     test("prioritizes custom headers over legacy auth", async () => {
diff --git a/client/src/lib/hooks/useConnection.ts b/client/src/lib/hooks/useConnection.ts
index 70ae5acf..fa03496d 100644
--- a/client/src/lib/hooks/useConnection.ts
+++ b/client/src/lib/hooks/useConnection.ts
@@ -400,6 +400,23 @@ export function useConnection({
       // Use custom headers (migration is handled in App.tsx)
       let finalHeaders: CustomHeaders = customHeaders || [];
 
+      // Check for empty Authorization headers and show validation error
+      const hasEmptyAuthHeader = finalHeaders.some(
+        (header) =>
+          header.enabled &&
+          header.name.trim().toLowerCase() === "authorization" &&
+          (!header.value.trim() || header.value.trim() === "Bearer"),
+      );
+
+      if (hasEmptyAuthHeader) {
+        toast({
+          title: "Invalid Authorization Header",
+          description:
+            "Authorization header is enabled but empty. Please add a token or disable the header. It will be added automatically.",
+          variant: "destructive",
+        });
+      }
+
       // Check if we need to inject OAuth token
       // This handles both empty headers and default "Bearer " placeholder headers
       const isEmptyAuthHeader = (header: CustomHeaders[number]) =>