diff --git a/assets/chrome-extension/background.js b/assets/chrome-extension/background.js
index 5ebe4008af3..94956571101 100644
--- a/assets/chrome-extension/background.js
+++ b/assets/chrome-extension/background.js
@@ -882,7 +882,18 @@ chrome.runtime.onMessage.addListener((msg, _sender, sendResponse) => {
   const { url, token } = msg
   const headers = token ? { 'x-openclaw-relay-token': token } : {}
   fetch(url, { method: 'GET', headers, signal: AbortSignal.timeout(2000) })
-    .then((res) => sendResponse({ status: res.status, ok: res.ok }))
+    .then(async (res) => {
+      const contentType = String(res.headers.get('content-type') || '')
+      let json = null
+      if (contentType.includes('application/json')) {
+        try {
+          json = await res.json()
+        } catch {
+          json = null
+        }
+      }
+      sendResponse({ status: res.status, ok: res.ok, contentType, json })
+    })
     .catch((err) => sendResponse({ status: 0, ok: false, error: String(err) }))
   return true
 })
diff --git a/assets/chrome-extension/options.js b/assets/chrome-extension/options.js
index 7a47a5d947e..96b87768dae 100644
--- a/assets/chrome-extension/options.js
+++ b/assets/chrome-extension/options.js
@@ -54,12 +54,39 @@ async function checkRelayReachable(port, token) {
     }
     if (res.error) throw new Error(res.error)
     if (!res.ok) throw new Error(`HTTP ${res.status}`)
+
+    // Validate that this is a CDP relay /json/version payload, not gateway HTML.
+    const contentType = String(res.contentType || '')
+    const data = res.json
+    if (!contentType.includes('application/json')) {
+      setStatus(
+        'error',
+        'Wrong port: this is likely the gateway, not the relay. Use gateway port + 3 (for gateway 18789, relay is 18792).',
+      )
+      return
+    }
+    if (!data || typeof data !== 'object' || !('Browser' in data) || !('Protocol-Version' in data)) {
+      setStatus(
+        'error',
+        'Wrong port: expected relay /json/version response. Use gateway port + 3 (for gateway 18789, relay is 18792).',
+      )
+      return
+    }
+
     setStatus('ok', `Relay reachable and authenticated at http://127.0.0.1:${port}/`)
-  } catch {
-    setStatus(
-      'error',
-      `Relay not reachable/authenticated at http://127.0.0.1:${port}/. Start OpenClaw browser relay and verify token.`,
-    )
+  } catch (err) {
+    const message = String(err || '').toLowerCase()
+    if (message.includes('json') || message.includes('syntax')) {
+      setStatus(
+        'error',
+        'Wrong port: this is not a relay endpoint. Use gateway port + 3 (for gateway 18789, relay is 18792).',
+      )
+    } else {
+      setStatus(
+        'error',
+        `Relay not reachable/authenticated at http://127.0.0.1:${port}/. Start OpenClaw browser relay and verify token.`,
+      )
+    }
   }
 }