diff --git a/client/src/components/PopupBlockedBanner.tsx b/client/src/components/PopupBlockedBanner.tsx
new file mode 100644
index 00000000..06025bdc
--- /dev/null
+++ b/client/src/components/PopupBlockedBanner.tsx
@@ -0,0 +1,152 @@
+import { useEffect, useState } from "react";
+import { Alert, AlertDescription } from "@/components/ui/alert";
+import { Button } from "@/components/ui/button";
+import { AlertCircle, ArrowUp, X } from "lucide-react";
+
+// Remembers a passed check so the test window doesn't flash on every reload.
+const POPUP_OK_KEY = "keylessh:popup-ok";
+
+/**
+ * Tide approvals run in a popup window (the approval enclave), so a browser
+ * that blocks popups breaks them. Probe once after login, outside a user
+ * gesture: that only succeeds when popups are allowed for this site.
+ */
+function popupsAllowed(): Promise<boolean> {
+  let w: Window | null = null;
+  try {
+    w = window.open("about:blank", "_blank", "width=1,height=1,left=-10000,top=-10000");
+  } catch {
+    return Promise.resolve(false);
+  }
+  if (!w || w.closed) return Promise.resolve(false);
+  // Some blockers hand back a window and then close it straight away.
+  return new Promise((resolve) => {
+    setTimeout(() => {
+      const ok = !w!.closed;
+      try {
+        w!.close();
+      } catch {
+        // ignore
+      }
+      resolve(ok);
+    }, 250);
+  });
+}
+
+type Browser = "edge" | "chrome" | "firefox" | "safari" | "other";
+
+function detectBrowser(): Browser {
+  const ua = navigator.userAgent;
+  if (/Edg\//.test(ua)) return "edge";
+  if (/Firefox\//.test(ua)) return "firefox";
+  if (/Chrome\/|Chromium\/|CriOS\//.test(ua)) return "chrome";
+  if (/Safari\//.test(ua)) return "safari";
+  return "other";
+}
+
+// Where the browser surfaces the blocked popup, and how to allow it from there.
+const UNBLOCK_STEPS: Record<Browser, string[]> = {
+  chrome: [
+    "Click the blocked-popup icon at the right end of the address bar (↑ top right).",
+    "Choose “Always allow pop-ups and redirects from this site”, then click Done.",
+    "Click Reload below.",
+  ],
+  edge: [
+    "Click the blocked-popup icon at the right end of the address bar (↑ top right).",
+    "Choose “Always allow pop-ups and redirects from this site”, then click Done.",
+    "Click Reload below.",
+  ],
+  firefox: [
+    "Find the yellow “Firefox prevented this site from opening a pop-up window” bar just below the address bar.",
+    "Click its Options (or Preferences) button on the right (↑ top right).",
+    "Choose “Allow pop-ups for this site”, then click Reload below.",
+  ],
+  safari: [
+    "Click the blocked-popup icon in the address bar (↑ top), or open Safari › Settings › Websites › Pop-up Windows.",
+    "Set this website to “Allow”.",
+    "Click Reload below.",
+  ],
+  other: [
+    "Look for a blocked-popup icon or notice near the address bar (↑ top right).",
+    "Allow pop-ups for this site.",
+    "Click Reload below.",
+  ],
+};
+
+export function PopupBlockedBanner() {
+  const [blocked, setBlocked] = useState(false);
+  const [browser] = useState(detectBrowser);
+
+  useEffect(() => {
+    try {
+      if (sessionStorage.getItem(POPUP_OK_KEY) === "1") return;
+    } catch {
+      // storage unavailable; just run the check
+    }
+    let cancelled = false;
+    popupsAllowed().then((ok) => {
+      if (cancelled) return;
+      if (ok) {
+        try {
+          sessionStorage.setItem(POPUP_OK_KEY, "1");
+        } catch {
+          // ignore
+        }
+      }
+      setBlocked(!ok);
+    });
+    return () => {
+      cancelled = true;
+    };
+  }, []);
+
+  if (!blocked) return null;
+
+  return (
+    <Alert
+      role="alert"
+      className="relative rounded-none border-x-0 border-t-0 bg-amber-50 border-amber-300 pr-24 dark:bg-amber-950/30 dark:border-amber-800"
+      data-testid="popup-blocked-banner"
+    >
+      <AlertCircle className="h-4 w-4 text-amber-600 dark:text-amber-400" />
+      <AlertDescription className="text-amber-900 dark:text-amber-100">
+        <p className="font-semibold">Pop-ups are blocked: please unblock them to use KeyleSSH.</p>
+        <p className="mt-0.5 text-amber-800 dark:text-amber-200">
+          Tide approvals open in a pop-up window and won&rsquo;t work until pop-ups are allowed for this site.
+        </p>
+        <ol className="mt-2 list-decimal space-y-0.5 pl-5 text-amber-800 dark:text-amber-200">
+          {UNBLOCK_STEPS[browser].map((step) => (
+            <li key={step}>{step}</li>
+          ))}
+        </ol>
+        <div className="mt-3 flex items-center gap-2">
+          <Button
+            size="sm"
+            className="bg-amber-600 text-white hover:bg-amber-700 dark:bg-amber-500 dark:text-amber-950 dark:hover:bg-amber-400"
+            onClick={() => window.location.reload()}
+          >
+            Reload
+          </Button>
+          <Button
+            size="sm"
+            variant="ghost"
+            className="text-amber-800 hover:bg-amber-100 dark:text-amber-200 dark:hover:bg-amber-950"
+            onClick={() => setBlocked(false)}
+          >
+            <X className="mr-1 h-4 w-4" />
+            Dismiss
+          </Button>
+        </div>
+      </AlertDescription>
+
+      {/* Points up at the address bar, where the browser shows its blocked-popup icon. */}
+      <div
+        className="pointer-events-none absolute right-6 top-1 flex flex-col items-center text-amber-600 dark:text-amber-400"
+        aria-hidden="true"
+      >
+        <ArrowUp className="h-10 w-10 animate-bounce" strokeWidth={2.5} />
+        <span className="-mt-1 text-xs font-semibold uppercase tracking-wide">Here</span>
+      </div>
+    </Alert>
+  );
+}
diff --git a/client/src/components/layout/AppLayout.tsx b/client/src/components/layout/AppLayout.tsx
index 34782a17..38ce03b0 100644
--- a/client/src/components/layout/AppLayout.tsx
+++ b/client/src/components/layout/AppLayout.tsx
@@ -1,5 +1,6 @@
 import { Link, useLocation } from "wouter";
 import { useAuth } from "@/contexts/AuthContext";
+import { PopupBlockedBanner } from "@/components/PopupBlockedBanner";
 import { Button } from "@/components/ui/button";
 import { Badge } from "@/components/ui/badge";
 import { Avatar, AvatarFallback } from "@/components/ui/avatar";
@@ -411,6 +412,8 @@ export function AppLayout({ children }: AppLayoutProps) {
         </Sidebar>
 
         <div className="flex flex-1 flex-col overflow-hidden">
+          <PopupBlockedBanner />
+
           <header className="flex h-14 items-center justify-between gap-2 sm:gap-4 border-b border-border bg-background px-2 sm:px-4">
             <div className="flex items-center gap-2 sm:gap-4 min-w-0">
               <SidebarTrigger data-testid="sidebar-trigger" className="h-10 w-10 shrink-0" />