diff --git a/src/app/layout.test.tsx b/src/app/layout.test.tsx
index 27d6e9d..9c93f17 100644
--- a/src/app/layout.test.tsx
+++ b/src/app/layout.test.tsx
@@ -1,5 +1,15 @@
-import { describe, expect, it } from "vitest";
+import { describe, expect, it, vi } from "vitest";
 import { render, screen } from "@testing-library/react";
+
+const { useGlobalErrorCaptureMock } = vi.hoisted(() => ({
+  useGlobalErrorCaptureMock: vi.fn(),
+}));
+
+// Stub out the global error capture hook — we test it in isolation
+vi.mock("@/hooks/useGlobalErrorCapture", () => ({
+  useGlobalErrorCapture: useGlobalErrorCaptureMock,
+}));
+
 import RootLayout from "./layout";
 
 describe("RootLayout", () => {
@@ -22,4 +32,13 @@ describe("RootLayout", () => {
 
     expect(screen.getByText("Skip to main content")).toHaveAttribute("href", "#main-content");
   });
+
+  it("mounts the global error capture hook", () => {
+    render(
+      <RootLayout>
+        <div />
+      </RootLayout>
+    );
+    expect(useGlobalErrorCaptureMock).toHaveBeenCalled();
+  });
 });
diff --git a/src/app/layout.tsx b/src/app/layout.tsx
index 543ea82..0cc934b 100644
--- a/src/app/layout.tsx
+++ b/src/app/layout.tsx
@@ -2,6 +2,7 @@ import type { Metadata, Viewport } from "next";
 import "./globals.css";
 import { WalletHydrator } from "@/components/WalletHydrator";
 import { ToastViewport } from "@/components/ToastViewport";
+import { GlobalErrorCapture } from "@/components/GlobalErrorCapture";
 import { I18nProvider } from "@/lib/i18n/I18nProvider";
 import { DEFAULT_LOCALE } from "@/lib/i18n";
 
@@ -92,6 +93,7 @@ export default function RootLayout({ children }: { children: React.ReactNode })
           Skip to main content
         </a>
         <I18nProvider locale={DEFAULT_LOCALE}>
+          <GlobalErrorCapture />
           <WalletHydrator />
           {children}
           <ToastViewport />
diff --git a/src/components/GlobalErrorCapture.tsx b/src/components/GlobalErrorCapture.tsx
new file mode 100644
index 0000000..33dd6ec
--- /dev/null
+++ b/src/components/GlobalErrorCapture.tsx
@@ -0,0 +1,17 @@
+"use client";
+
+import { useGlobalErrorCapture } from "@/hooks/useGlobalErrorCapture";
+
+/**
+ * GlobalErrorCapture
+ *
+ * A renderless client component that mounts the global error and
+ * unhandledrejection listeners for the lifetime of the application.
+ *
+ * Place it once, high in the tree (e.g. inside RootLayout), so that it is
+ * always mounted regardless of which route is active.
+ */
+export function GlobalErrorCapture(): null {
+  useGlobalErrorCapture();
+  return null;
+}
diff --git a/src/hooks/useGlobalErrorCapture.test.ts b/src/hooks/useGlobalErrorCapture.test.ts
new file mode 100644
index 0000000..52812c9
--- /dev/null
+++ b/src/hooks/useGlobalErrorCapture.test.ts
@@ -0,0 +1,171 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { renderHook, act } from "@testing-library/react";
+
+const { addToastMock } = vi.hoisted(() => ({
+  addToastMock: vi.fn(),
+}));
+
+vi.mock("@/store/toast", () => ({
+  useToastStore: { getState: () => ({ addToast: addToastMock }) },
+}));
+
+import { useGlobalErrorCapture } from "./useGlobalErrorCapture";
+
+describe("useGlobalErrorCapture", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    vi.spyOn(console, "error").mockImplementation(() => {});
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it("registers window 'error' and 'unhandledrejection' listeners on mount", () => {
+    const addSpy = vi.spyOn(window, "addEventListener");
+    renderHook(() => useGlobalErrorCapture());
+
+    expect(addSpy).toHaveBeenCalledWith("error", expect.any(Function));
+    expect(addSpy).toHaveBeenCalledWith("unhandledrejection", expect.any(Function));
+  });
+
+  it("removes both listeners on unmount", () => {
+    const removeSpy = vi.spyOn(window, "removeEventListener");
+    const { unmount } = renderHook(() => useGlobalErrorCapture());
+    unmount();
+
+    expect(removeSpy).toHaveBeenCalledWith("error", expect.any(Function));
+    expect(removeSpy).toHaveBeenCalledWith("unhandledrejection", expect.any(Function));
+  });
+
+  it("forwards a synchronous ErrorEvent to the toast store", () => {
+    renderHook(() => useGlobalErrorCapture());
+
+    act(() => {
+      const event = new ErrorEvent("error", {
+        error: new Error("Something exploded"),
+        message: "Something exploded",
+      });
+      window.dispatchEvent(event);
+    });
+
+    expect(addToastMock).toHaveBeenCalledWith("Something exploded", "error");
+  });
+
+  it("handles an ErrorEvent with no error object (message fallback)", () => {
+    renderHook(() => useGlobalErrorCapture());
+
+    act(() => {
+      const event = new ErrorEvent("error", { message: "script error from string" });
+      window.dispatchEvent(event);
+    });
+
+    expect(addToastMock).toHaveBeenCalledWith("script error from string", "error");
+  });
+
+  it("invokes the unhandledrejection handler with an Error reason", () => {
+    // jsdom does not define PromiseRejectionEvent, so we call the listener
+    // directly by capturing it from addEventListener.
+    const handlers = new Map<string, EventListener>();
+    const addSpy = vi.spyOn(window, "addEventListener").mockImplementation(
+      (type: string, listener: EventListenerOrEventListenerObject) => {
+        handlers.set(type, listener as EventListener);
+      }
+    );
+
+    renderHook(() => useGlobalErrorCapture());
+
+    const handler = handlers.get("unhandledrejection");
+    expect(handler).toBeDefined();
+
+    act(() => {
+      handler!({ type: "unhandledrejection", reason: new Error("Promise blew up") } as unknown as Event);
+    });
+
+    expect(addToastMock).toHaveBeenCalledWith("Promise blew up", "error");
+    addSpy.mockRestore();
+  });
+
+  it("handles a string rejection reason", () => {
+    const handlers = new Map<string, EventListener>();
+    const addSpy = vi.spyOn(window, "addEventListener").mockImplementation(
+      (type: string, listener: EventListenerOrEventListenerObject) => {
+        handlers.set(type, listener as EventListener);
+      }
+    );
+
+    renderHook(() => useGlobalErrorCapture());
+
+    const handler = handlers.get("unhandledrejection")!;
+    act(() => {
+      handler({ type: "unhandledrejection", reason: "plain string error" } as unknown as Event);
+    });
+
+    expect(addToastMock).toHaveBeenCalledWith("plain string error", "error");
+    addSpy.mockRestore();
+  });
+
+  it("uses a fallback message for null rejection reasons", () => {
+    const handlers = new Map<string, EventListener>();
+    const addSpy = vi.spyOn(window, "addEventListener").mockImplementation(
+      (type: string, listener: EventListenerOrEventListenerObject) => {
+        handlers.set(type, listener as EventListener);
+      }
+    );
+
+    renderHook(() => useGlobalErrorCapture());
+
+    const handler = handlers.get("unhandledrejection")!;
+    act(() => {
+      handler({ type: "unhandledrejection", reason: null } as unknown as Event);
+    });
+
+    expect(addToastMock).toHaveBeenCalledWith("An unexpected error occurred.", "error");
+    addSpy.mockRestore();
+  });
+
+  it("truncates very long error messages", () => {
+    renderHook(() => useGlobalErrorCapture());
+
+    const longMessage = "x".repeat(200);
+    act(() => {
+      const event = new ErrorEvent("error", {
+        error: new Error(longMessage),
+        message: longMessage,
+      });
+      window.dispatchEvent(event);
+    });
+
+    const [toastMsg] = addToastMock.mock.calls[0] as [string, string];
+    expect(toastMsg.length).toBeLessThanOrEqual(121); // 120 chars + ellipsis
+    expect(toastMsg.endsWith("…")).toBe(true);
+  });
+
+  it("does not fire after the component unmounts", () => {
+    // Spy on removeEventListener to confirm it is called on cleanup.
+    const removeSpy = vi.spyOn(window, "removeEventListener");
+    const { unmount } = renderHook(() => useGlobalErrorCapture());
+
+    unmount();
+
+    // Both listeners must be deregistered so no more toasts appear.
+    expect(removeSpy).toHaveBeenCalledWith("error", expect.any(Function));
+    expect(removeSpy).toHaveBeenCalledWith("unhandledrejection", expect.any(Function));
+    // No toasts were fired during this test.
+    expect(addToastMock).not.toHaveBeenCalled();
+  });
+
+  it("also logs via console.error", () => {
+    renderHook(() => useGlobalErrorCapture());
+
+    act(() => {
+      const event = new ErrorEvent("error", {
+        error: new Error("logged error"),
+        message: "logged error",
+      });
+      window.dispatchEvent(event);
+    });
+
+    expect(console.error).toHaveBeenCalled();
+  });
+});
diff --git a/src/hooks/useGlobalErrorCapture.ts b/src/hooks/useGlobalErrorCapture.ts
new file mode 100644
index 0000000..dbd79aa
--- /dev/null
+++ b/src/hooks/useGlobalErrorCapture.ts
@@ -0,0 +1,59 @@
+/**
+ * useGlobalErrorCapture
+ *
+ * Attaches window-level listeners for two browser error channels that React
+ * does NOT intercept automatically:
+ *
+ * - "error"              — synchronous errors thrown in event handlers,
+ *                          setTimeout/setInterval callbacks, and any context
+ *                          outside React's render cycle.
+ * - "unhandledrejection" — Promises that are rejected without a .catch() or
+ *                          try/catch — common in fire-and-forget async calls.
+ *
+ * Both are forwarded to the shared toast store as "error" notifications and
+ * also logged via console.error so they still appear in DevTools.
+ *
+ * The hook is intentionally side-effect-only (no return value) and is safe
+ * to call at the top of the component tree (e.g. RootLayout's client shell).
+ */
+"use client";
+
+import { useEffect } from "react";
+import { useToastStore } from "@/store/toast";
+
+/** Maximum characters shown in the toast for an error message. */
+const MAX_MSG_LENGTH = 120;
+
+function truncate(msg: string): string {
+  return msg.length <= MAX_MSG_LENGTH ? msg : `${msg.slice(0, MAX_MSG_LENGTH)}…`;
+}
+
+function extractMessage(err: unknown): string {
+  if (err instanceof Error) return err.message || err.toString();
+  if (typeof err === "string" && err.trim()) return err;
+  return "An unexpected error occurred.";
+}
+
+export function useGlobalErrorCapture(): void {
+  useEffect(() => {
+    const handleError = (event: ErrorEvent): void => {
+      const message = extractMessage(event.error ?? event.message);
+      console.error("[GlobalErrorCapture] Uncaught error:", event.error ?? event.message);
+      useToastStore.getState().addToast(truncate(message), "error");
+    };
+
+    const handleUnhandledRejection = (event: PromiseRejectionEvent): void => {
+      const message = extractMessage(event.reason);
+      console.error("[GlobalErrorCapture] Unhandled rejection:", event.reason);
+      useToastStore.getState().addToast(truncate(message), "error");
+    };
+
+    window.addEventListener("error", handleError);
+    window.addEventListener("unhandledrejection", handleUnhandledRejection);
+
+    return () => {
+      window.removeEventListener("error", handleError);
+      window.removeEventListener("unhandledrejection", handleUnhandledRejection);
+    };
+  }, []);
+}