diff --git a/vibn-frontend/app/api/chat/route.ts b/vibn-frontend/app/api/chat/route.ts
index 10420e1..c455e2c 100644
--- a/vibn-frontend/app/api/chat/route.ts
+++ b/vibn-frontend/app/api/chat/route.ts
@@ -501,6 +501,13 @@ export async function POST(request: Request) {
     chatMode = "vibe",
     attachedFiles = [],
   } = body;
+
+  // Sanitise the incoming token to handle empty strings or "undefined" hydration states cleanly
+  const activeMcpToken =
+    mcp_token && mcp_token !== "undefined" && mcp_token.trim() !== ""
+      ? mcp_token.trim()
+      : undefined;
+
   if (!thread_id || !message?.trim()) {
     return NextResponse.json(
       { error: "thread_id and message are required" },
@@ -850,7 +857,7 @@ export async function POST(request: Request) {
         return conversationalPatterns.some((re) => re.test(m));
       }
       const firstMessageIsConversational =
-        mcp_token !== undefined && // tools available
+        activeMcpToken !== undefined && // tools available
         isConversational(message.trim());
 
       try {
@@ -863,7 +870,7 @@ export async function POST(request: Request) {
           // Keep tool definitions active in the schema to avoid model confusion and
           // MALFORMED_FUNCTION_CALL gateway crashes, but let our system instructions
           // guide the model to respond in plain text for conversational inputs.
-          const toolDefs = mcp_token ? VIBN_TOOL_DEFINITIONS : [];
+          const toolDefs = activeMcpToken ? VIBN_TOOL_DEFINITIONS : [];
 
           // Every 8 silent rounds or 12 tool calls, gently nudge the model to surface a one-liner
           // status before continuing. This is the user's only signal of
@@ -995,11 +1002,11 @@ export async function POST(request: Request) {
                 TOOL_TIMEOUT_MS,
               ),
             );
-            const toolExec = mcp_token
+            const toolExec = activeMcpToken
               ? executeMcpTool(
                   tc.name,
                   tc.args,
-                  mcp_token,
+                  activeMcpToken,
                   baseUrl,
                   activeProject?.id,
                 )